instructor’s manual for e...natural processes such as volcanic eruptions, earthquakes, floods, and...

Instructor Manual

Natural Hazards Earth’s Processes as Hazards, Disasters,

and Catastrophes Third Edition

Patricia Anderson California State University – San Marcos

© 2012 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from

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Chapter 1 Introduction to Natural Hazards Learning Objectives Natural processes such as volcanic eruptions, earthquakes, floods, and hurricanes become hazards when they threaten human life and property. As population continues to grow, hazards, disasters, and catastrophes become more common. An understanding of natural processes as hazards requires some basic knowledge of Earth science. Your goals in reading this chapter should be to

• know the difference between a disaster and a catastrophe. • know the components and processes of the geologic cycle. • understand the scientific method. • understand the basics of risk assessment. • recognize that natural hazards that cause disasters are generally high-energy

events, caused by natural Earth processes. • understand the concept that the magnitude of a hazardous event is inversely

related to its frequency. • understand how natural hazards may be linked to one another and to the

physical environment. • recognize that increasing human population and poor land use changes

compound the effects of natural hazards, turning disasters into catastrophes.

Chapter Outline 1. Introduction to Natural Hazards

1.1. Why Studying Natural Hazards Is Important 1.1.1. Processes: Internal and External 1.1.2. Hazard, Disaster, or Catastrophe 1.1.3. Death and Damage Caused by Natural Hazards

1.2. Role of History in Understanding Hazards 1.3. Geologic Cycle

1.3.1. The Tectonic Cycle 1.3.2. The Rock Cycle 1.3.3. The Hydrologic Cycle 1.3.4. Biogeochemical Cycles

1.4. Fundamental Concepts for Understanding Natural Processes as Hazards 1.4.1. Science and Natural Hazards 1.4.2. Hazards Are Natural Processes 1.4.3. Forecast, Prediction, and Warning of Hazardous Events 1.4.4. Examples of Disasters In Densely Populated Areas 1.4.5. Human Population Growth


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1.4.6. Magnitude and Frequency of Hazardous Events Case Study 1.1: Human Population through History Case Study 1.2: The Magnitude–Frequency Concept

1.4.7. Reactive Response: Impact of and Recovery from Disasters 1.4.8. Anticipatory Response: Avoiding and Adjusting to Hazards

1.5. Many Hazards Provide a Natural Service Function 1.6. Global Climate Change and Hazards

Chapter Summary Natural hazards are responsible for causing significant death and damage worldwide each year. Processes that cause hazardous events include those that are internal to Earth, such as volcanic eruptions and earthquakes that result from Earth’s internal heat, and those that are external to the Earth, such as hurricanes and global warming, which are driven by energy from the sun.

Natural processes may become hazards, disasters, or catastrophes when they interact with human beings. Central to an understanding of natural hazards is awareness that hazardous events result from natural processes that have been in operation for millions and possibly billions of years before humans experienced them. These processes become hazards when they threaten human life or property and should be recognized and avoided.

Hazards involve repetitive events. Thus, a study of the history of these events provides much-needed information for hazard reduction. A better understanding and more accurate prediction of natural processes come by integrating historic and prehistoric information, present conditions, and recent past events, including land-use changes.

Geologic conditions and materials largely govern the type, location, and intensity of natural processes. The geologic cycle creates, maintains, and destroys Earth materials by physical, chemical, and biological processes. Subcycles of the geologic cycle are the tectonic cycle, rock cycle, hydrologic cycle, and various biogeochemical cycles. The tectonic cycle describes large-scale geologic processes that deform Earth’s crust, producing landforms such as ocean basins, continents, and mountains. The rock cycle may be considered a worldwide earth-material recycling process driven by Earth’s internal heat, which melts the rocks subducted in the tectonic cycle. Driven by solar energy, the hydrologic cycle operates by way of evaporation, precipitation, surface runoff, and subsurface flow. Biogeochemical cycles can most easily be described as the transfer of chemical elements through a series of storage compartments or reservoirs, such as air or vegetation.

Five fundamental concepts establish a philosophical framework for studying natural hazards.

1. Hazards are predictable from scientific evaluation.

2. Risk analysis is an important component in our understanding of the effects of

hazardous processes.


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3. Linkages exist between various natural hazards as well as between hazards and

the physical environment.

4. Hazardous events that previously produced disasters are now producing catastrophes.

5. Consequences of hazards can be minimized.

Answers to Review Questions: 1. What forces drive internal and external Earth processes? (p. 3)

Internal forces are processes deep within the Earth, driven by plate tectonics and heat loss from Earth’s deep interior. External forces are processes that take place near the surface or at the surface of the Earth and are driven by gravity and energy from the Sun.

2. What is the distinction between a natural hazard, disaster, and catastrophe? (p. 3)

A natural hazard is any natural process that poses a threat to human life or property. A disaster occurs when a hazard, such as a flood or earthquake, inflicts loss of life and property in a society. A catastrophe is a massive disaster, typically with many deaths, requiring a large input of time and money to rectify.

3. Which natural hazards are likely to be more deadly, more likely to cause property damage, and more likely to become catastrophes? (pp. 3–5)

Tornados, windstorms, floods, and hurricanes are all likely to cause property damage and are more likely to become catastrophes. Earthquake, volcanic, and tsunami hazards have historically caused the greatest number of deaths, even though they occur less frequently than the weather-related catastrophes.

4. Explain why the effects of natural hazards are not constant over time. (p. 6) The effects of natural hazards change with time because of changes in land-use patterns.

5. Why is history so important in understanding natural hazards? (p. 7)

Studying history provides the needed background to guide any hazard reduction plan. Specifically, history can reveal the recurrence interval for hazards such as


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floods, earthquakes, and other hazards that occur with a semi-regular frequency.

6. What kinds of information must be assembled to make hazard predictions? (p. 7)

A prediction of the future occurrence and effects of a hazard requires that we combine information about historic and prehistoric behavior with a knowledge of present conditions and recent past events, including land-use changes.

7. Describe the components and interactions involved in the geologic cycle. (pp. 7–9) The Tectonic Cycle: This involves the creation, movement, and destruction of tectonic plates through geologic process driven by forces deep within Earth. Tectonic processes largely determine the quality of rocks and soils produced at plate boundaries, for which we depend on building and agriculture. Tectonics also affects the flow patterns of the oceans, which in turn influence global climate and precipitation. The Rock Cycle: The largest of the subcycles, it is linked to all the other subcycles. It depends on tectonics for heat and energy, the biogeochemical cycle for materials, and the hydrologic cycle for water. Water is then used in the process of weathering, erosion, transportation, deposition, and lithification of sediment. The Hydrologic Cycle: Driven by solar energy, this cycle moves water from the oceans to the atmosphere and back again. It operates by way of evaporation, precipitation, surface runoff, and subsurface flow, storing water in different compartments along the way. The water produced from the hydrologic cycle helps move and sort chemical elements in solution, sculpt the landscape, weather rocks, transport and deposit sediments, and provide our water resources. The Biogeochemical Cycle: This is the transfer or cycling of an element or elements through the atmosphere, lithosphere, hydrosphere, and biosphere. Chemical elements are transferred through a series of storage compartments or reservoirs, such as air, soil, groundwater, or vegetation. The biogeochemical cycle is tied to the tectonic, rock, and hydrologic cycles.

8. What are the five fundamental concepts for understanding natural processes as hazards? (pp. 9–10)

The five fundamental concepts are as follows: Hazards are predictable from scientific evaluation. Risk analysis is important to understand the effects of hazardous processes.


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Linkages exist between different natural hazards as well as between hazards and the physical environment.

Hazardous events that previously produced disasters are now producing catastrophes.

Consequences of hazards can be minimized.

9. Explain the scientific method as it is applied to natural hazards. (p. 10)

The scientific method is a series of steps that begins with the formulation of a question or series of questions, and includes one or more hypotheses that can be tested through observation and experimentation. Use of the scientific method has improved our understanding of many natural Earth processes.

10. Explain why calling something a “natural” hazard may act as a philosophical barrier

to dealing with it. (p. 10) Because the hazards that we face are natural and not the result of human activities, we encounter a philosophical barrier whenever we try to minimize their adverse effects. However, most natural hazards are completely beyond our control, and we may actually worsen the effects of natural processes simply by labeling them as hazardous, as this usually leads to attempts to control them. Since natural Earth processes only become hazardous when people live or work near them, and when land-use changes such as urbanization and deforestation amplify their effect, the best approach to hazard reduction is to identify hazardous process and delineate the geographic areas where they occur. People could then avoid putting themselves and their property in harm’s way, especially for those hazards, such as earthquakes, volcanoes, and floods, which we cannot control.

11. What are the elements involved in making a hazard forecast and warning? (p. 13)

• Identifying the location where a hazardous event is likely to occur. • Determining the probability that an event of a given magnitude will occur. • Observing any precursor events. • Forecasting or predicting the event. • Warning the public.

12. Explain why two 10-year floods might occur in the same year. (p. 13)

The term 10-year flood only states the statistical chance that a flood of a certain magnitude typically only occurs once every 10 years, averaged over a long time interval. For instance, two floods of this magnitude could happen in one year, then none for the next 20 years.


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13. What is a precursor event? Give some examples. (p. 13) A precursor event is an event that precedes, occurs before, a hazardous event. For example, the surface of the ground may creep prior to a landslide, volcanoes often swell or bulge before an eruption, and foreshocks or unusual uplift of the land may precede earthquakes.

14. Explain the magnitude–frequency concept. (p. 18)

Larger, more destructive disasters happen infrequently, whereas smaller, less destructive disasters happen more frequently. Planners need to be prepared for larger events but should not neglect the management of smaller events.

15. How do risk and acceptable risk differ? (p. 14)

Risk is the product of the probability of the event occurring times the consequences should it occur. Acceptable risk is the risk society and individuals are willing to take depending on a given situation.

16. Explain how population growth increases the number of disasters and catastrophes.

(pp. 16–17) The more people there are on Earth, the more likely chance any disaster has of affecting them, and affecting them to a greater extent. As population increases, more people move into areas that are hazardous to live, such as shorelines, steep slopes, and near active faults and volcanoes. Disasters become catastrophes when more people die.

17. Describe the differences between direct and indirect effects of disasters. (p. 19)

Direct effects include people killed, injured, dislocated, or otherwise damaged by a particular event, such as being buried by volcanic ash or killed by falling debris in an earthquake. Indirect effects are responses to the disaster, such as emotional distress, donation of money or goods, and paying of taxes levied to finance the recovery. Direct effects are felt by fewer individuals, whereas indirect effects affect many more people.

18. What are the stages of disaster recovery? How do they differ? (p. 19)

The stages of disaster recovery are emergency work, restoration of services and communication lines, and reconstruction. Emergency work is the work that must be done immediately to save lives. Restoration and communication lines include providing temporary shelter and communication. Reconstruction includes getting lives back to normal for everyone.


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19. Describe four common adjustments to natural hazards. (p. 20) Four adjustments to natural hazards are insurance, evacuation, disaster preparedness, and artificial control of natural processes.

20. What are natural service functions? (p. 21)

Natural service functions are the important benefits that most of these natural events provide in some way.

Answers to Critical Thinking Questions: 1. How would you use the scientific method to test the hypothesis that sand on the beach

comes from the nearby mountains? You would have to establish that the sand on the beach and the rocks in the mountains had the same chemical makeup and were of the same age to prove this theory.

2. It has been argued that we must control human population because otherwise we

won’t be able to feed everyone. Even if we could feed 10 to 15 billion people, would we still want a smaller population? Why or why not?

We still want a smaller population because the most important issue in hazard mitigation is not food production. If a population is so big that people are living near potentially hazardous areas, these people are more likely to be at risk. Decreasing the population would allow people to live in safer areas. It would also allow for less pollution and better waste disposal.

3. Considering that events we call natural hazards are natural processes that have been

occurring on the Earth for millions of years, how do you think we should go about trying to prevent loss of life from these events? Think about the choices that society has, from attempting to control and prevent hazards to attempting to keep people out of harm’s way.

We cannot prevent natural disasters, so focusing on population awareness of disasters and good disaster evacuation planning would be the best ways to try to prevent the loss of life due to these events. Planners should try not to develop areas that are hazardous and prone to disasters such as floodplains, steep slopes, and near active faults.


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4. Global warming is a major concern today. Discuss how global warming might influence the magnitude or frequency of hazardous events, disasters, or catastrophes caused by natural hazards.

Global warming is likely to affect the incidence of hazardous natural events such as storms, landslides, drought, and fires. With global warming, sea level is rising as the heating of seawater expands the volume of the ocean, and glacial ice is melting. As a result, coastal erosion will increase. Climate change may shift food production areas as some receive more precipitation and others receive less. Deserts and semiarid areas will likely expand, and warmer northern latitudes could become more productive. Such changes could lead to global population shifts, which might bring about wars or major social and political upheavals. Global warming will feed more energy from warmer ocean water into the atmosphere; this energy is likely to increase the severity and frequency of hazardous weather such as thunderstorms and hurricanes. In fact, this trend may already be underway—a recent analysis of global extreme-weather events by a United Nations panel indicates that since the 1950s there has been an increase in heavy precipitation events in mid-latitude regions and, since the 1970s, a likely increase in the intensity of hurricanes.

Suggested Activities 1. Compare population density map with hazardous regions. Different types of hazards:

coastal regions and regions that are within close proximity to fault zones and volcanoes.

2. Collect and discuss newspaper clippings of different hazards that occur around the

world on a daily basis. Additional Resources (media, film, articles, journals, web sites) Print Resources Dealing with Natural Hazards Abbott, P.L., 2012, Natural Disasters, 8th ed., McGraw Hill, Boston, 512 pp. ISBN-10 0-07-336937-3. Bryant, E.A., 1993, Natural Hazards, Cambridge University Press, Cambridge, 294 pp. Eldredge, N., 1998, Life in the Balance, Princeton University Press, Princeton, 224 pp.


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Erikson, J., 2001, Quakes, Eruptions, and other Geologic Cataclysms, Revealing the Earth’s Hazards, Facts on File Science Library, The Living Earth Series, New York, 310 pp.

Griggs, G.B., and Gilchrist, J.A., 1983, Geologic Hazards, Resources, and Environmental Planning, Belmont, CA, Wadsworth Publishing Co., 502 pp.

Keller, E.A., 2000, Environmental Geology, eighth ed., Prentice Hall, Englewood Cliffs, N.J., 562 pp.

Kusky, T.M., 2004, Encyclopedia of Earth Science, 528 pages, Facts on File, New York, ISBN 0816049734.

Kusky, T.M., 2003, Geological Hazards: A Sourcebook, an Oryx Book, Greenwood Press, Westport, Conn., 300 pp., ISBN 1-57356-469-9.

Mackenzie, F.T., and Mackenzie, J.A., 1995, Our Changing Planet: An Introduction to Earth System Science and Global Environmental Change, Prentice Hall, Englewood Cliffs, N.J., 387 pp.

Murck, B.W., Skinner, B.J., and Porter, S.C., 1997, Dangerous Earth: An Introduction to Geologic Hazards, John Wiley and Sons, New York, 300 pp.

Skinner, B.J., and Porter, B.J., 1989, The Dynamic Earth: An Introduction to Physical Geology, John Wiley and Sons, New York, 541 pp.

Nonprint Sources Dealing with Natural Hazards http://edcwww.cr.usgs.gov/ EROS Data Center lists satellite images, land cover maps, elevation models, maps, and aerial photography useful for Natural Hazards Studies. NASA’s web site on Natural Hazards: http://earthobservatory.nasa.gov/NaturalHazards/ NASA’s Earth observatory lists satellite images of natural hazards, including dust, smoke, fires, floods, severe storms, and volcanoes. USGS web site for Natural Hazards: http://www.usgs.gov/themes/hazard.html USGS activities in the hazards theme area deal with describing, documenting, and understanding natural hazards and their risks. The web page contains explanations of individual hazards, geographic distribution of hazards, and fact sheets on hazards. The site also has links describing USGS involvement in recent hazards. http://www.accuweather.com/ WeatherMatrix is a worldwide organization of over 3000 amateur and professional weather enthusiasts—meteorologists, storm chasers and spotters, and weather observers from all parts of the globe. WeatherMatrix was formerly the Central Atlantic Storm Investigators (CASI). Has frequently updated news about weather-related disasters. http://www.colorado.edu/hazards/


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This web site is the online version of the periodical, The Natural Hazards Observer. It contains features about various hazards and disasters. It also provides information of emergency management, research, politics, and education of natural disasters. Organizations Dealing with Natural Hazards Congressional Natural Hazards Work Group is a cooperative endeavor between a group of private and public organizations, whose goal is to develop a wider understanding within Congress of the value of reducing the risks and costs of natural disasters. The work group supports the effort of the Congressional Natural Hazards Caucus. Information on the Natural Hazards Caucus Work Group can be found at: http://www.agiweb.org/gap/workgroup/legislation109.html. Some of the lead organizations include the American Meteorological Society and University Corporation for Atmospheric Research (http://www.ucar.edu) and the National Science Foundation (http//www.nsf.gov). Federal Emergency Management Agency FEMA 500 C Street SW Washington, D.C. 20472 202-646-4600 http://www.fema.gov FEMA is the nation’s premier agency that deals with emergency management and preparation, and issues warnings and evacuation orders when disasters appear imminent. FEMA maintains a web site that is updated at least daily and includes information on hurricanes, floods, fires, national flood insurance, and disaster prevention, preparation, and emergency management. Divided into national and regional sites. Also contains information on costs of disasters, maps, and directions on how to do business with FEMA. U.S. Geological Survey U.S. Department of the Interior 345 Middlefield Road Menlo Park, CA 94025 650-329-5042 Also, offices in Reston, VA, Denver, CO http://www.usgs.gov/ The USGS is responsible for making maps of many of the different types of hazards discussed in this book, including earthquake and volcano hazards, tsunami, floods, landslides, and radon. The USGS National Landslide Information Center web site is http://landslides.usgs.gov/. National Oceanographic and Atmospheric Administration (NOAA) http://www.noaa.gov/ NOAA conducts research and gathers data about the global oceans, atmosphere, space, and sun, and applies this knowledge to science and service that touch lives of all


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Americans. NOAA’s mission is to describe and predict changes in Earth’s environment, and conserve and wisely manage the nation’s coastal and marine resources. NOAA’s strategy consists of seven interrelated strategic goals for environmental assessment, prediction, and stewardship. These include (1) advance short-term warnings and forecast services, (2) implement season to interannual climate forecasts, (3) assess and predict decadal to centennial change, (4) promote safe navigation, (5) build sustainable fisheries, (6) recover protected species, and (7) sustain healthy coastal ecosystems. NOAA runs a web site that includes links to current satellite images of weather hazards, issues warnings of current coastal hazards and disasters, and has an extensive historical and educational service. The National Hurricane Center, http://www.nhc.noaa.gov/, is a branch of NOAA, and posts regular updates of hurricane paths and hazards. The National Drought Mitigation Center http://www.drought.unl.edu/ The National Drought Mitigation Center helps people and institutions develop and implement measures to reduce societal vulnerability to drought. The NDMC, based at the University of Nebraska-Lincoln, stresses preparation and risk management rather than crisis management.


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Chapter 2 Internal Structure of Earth and Plate Tectonics Learning Objectives The surface of Earth would be much different—relatively smooth, with monotonous topography—if not for the active tectonic processes within Earth that produce earthquakes, volcanoes, mountain chains, continents, and ocean basins. In this chapter, we focus directly on the interior of Earth. Your goals in reading this chapter should be to

• understand the basic internal structure and processes of Earth. • know the basic ideas behind and evidence for the theory of plate tectonics. • understand the mechanisms of plate tectonics. • understand the relationship of plate tectonics to natural hazards.

Chapter Outline 2. Internal Structure of Earth and Plate Tectonics

2.1. Internal Structure of Earth 2.1.1. The Earth Is Layered and Dynamic 2.1.2. Continents and Ocean Basins Have Significantly Different Properties

2.2. How We Know about the Internal Structure of the Earth 2.2.1. What We Have Learned about Earth from Earthquakes

2.3. Plate Tectonics 2.3.1. Movement of the Lithospheric Plates

2.3.1.1. What Is a Plate? 2.3.1.2. Locations of Earthquakes and Volcanoes Define Plate Boundaries 2.3.1.3. Seafloor Spreading Is the Mechanism for Plate Tectonics 2.3.1.4. Sinking Plates Generate Earthquakes 2.3.1.5. Plate Tectonics Is a Unifying Theory

2.3.2. Types of Plate Boundaries A Closer Look 2.1: The Wonder of Mountains 2.3.3. Rate of Plate Motion

2.4. A Detailed Look at Sea Floor Spreading 2.4.1. Paleomagnetism

2.4.1.1. Earth’s Magnetic Field Periodically Reverses 2.4.1.2. What Produces Magnetic Stripes? 2.4.1.3. Why Is the Seafloor No Older than 200 Million Years?

2.4.2. Hot Spots 2.5. Pangaea and Present Continents 2.6. How Plate Tectonics Works: Putting It Together


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2.7. Plate Tectonics and Hazards Chapter Summary

Our knowledge concerning the structure of Earth’s interior is based on the study of seismology. Thus we are able to define the major layers of Earth, including the inner core, outer core, mantle, and crust. The uppermost layer of Earth is known as the lithosphere, which is relatively strong and rigid compared with the soft asthenosphere found below it. The lithosphere is broken into large pieces called plates that move relative to one another. As these plates move, they carry along the continents embedded within them. This process of plate tectonics produces large landforms, including continents, ocean basins, mountain ranges, and large plateaus. Oceanic basins are formed by the process of seafloor spreading and are destroyed by the process of subduction, both of which result from convection within the mantle.

The three types of plate boundaries are divergent (midoceanic ridges, spreading centers), convergent (subduction zones and continental collisions), and transform faults. At some locations, three plates meet in areas known as triple junctions. Rates of plate movement are generally a few centimeters per year.

Evidence supporting seafloor spreading includes paleomagnetic data, the configurations of hot spots and chains of volcanoes, and reconstructions of past continental positions.

The driving forces in plate tectonics are ridge push and slab pull. At present, we believe the process of slab pull is more significant than ridge push for moving tectonic plates from spreading centers to subduction zones.

Plate tectonics is extremely important in determining the occurrence and frequency of volcanic eruptions, earthquakes, and other natural hazards.

Answers to Review Questions: 1. What are the major differences between the inner and outer cores of Earth? (p. 27)

The inner core is solid with a thickness of more than 1300 km (808 mi) that is roughly the size of the moon but with a temperature about as high as the temperature of the surface of the sun. The inner core is believed to be primarily metallic, composed mostly of iron (about 90 percent by weight), with minor amounts of elements such as sulfur, oxygen, and nickel. Whereas the outer core is liquid with a thickness of just over 2000 km (1243 mi.) with a composition similar to that of the inner core.

2. How are the major properties of the lithosphere different from those of the

asthenosphere? (pp. 27–32)


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The lithosphere includes the crust and part of the mantle, and the asthenosphere is located entirely within the mantle. The lithosphere is broken into large ridged pieces called lithospheric plates that move relative to one another (Figure 2.5a). Processes associated with the creation, movement, and destruction of these plates are collectively known as plate tectonics. The outer layer (or lithosphere) is approximately 100 km (approximately 62 mi.) thick and is stronger and more rigid than the deeper asthenosphere, which is a hot and slowly flowing layer of relatively low-strength rock.

3. What are the three major types of plate boundaries? (pp. 32–34)

There are three basic types of plate boundaries: divergent, convergent, and transform. These boundaries are zones that range from a few to hundreds of kilometers across. Plate boundary zones are narrower in ocean crust and broader in continental crust. Divergent boundaries occur where new lithosphere is being produced and neighboring parts of plates are moving away from each other. Typically this process occurs at midocean ridges, and the process is called seafloor spreading. Convergent boundaries occur where plates collide. They can be divided into three sub groups: Oceanic–Continental Boundary, Oceanic–Oceanic Boundary and Continental–Continental Boundary.

Oceanic–Continental Boundary: When oceanic and continental plates converge, the oceanic plate must subduct beneath the continental plate

ecause the density of thick continental crust is too low to permit it to sink nto the asthenosphere.

bi Oceanic–Oceanic Boundary: When a convergent boundary forms

etween plates of oceanic lithosphere, the plate that is older, thicker, and enser subducts the less dense plate.

bd Continental–Continental Boundary: When subduction brings two continents together, limited subduction may occur, but the buoyancy of continental crust eventually stops the subduction. The contraction of crust in the collision zone doubles the thickness of continental crust and creates high mountains. Slivers of oceanic crust are commonly uplifted in the mountain range and record the basin consumed by subduction prior to collision of the continents.

Transform boundaries, or transform faults, occur where the edges of two plates slide past each other. Transform boundaries are generally found in two settings. Most are located on the sea floor offsetting ridge axes. Some occur within continents such as the San Andreas Fault in California.


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4. What is the major process that is thought to produce Earth’s magnetic field? (p. 38)

Convection occurs in the iron-rich, fluid, hot outer core of Earth because of compositional changes and heat at the inner–outer core boundary. As more buoyant material in the outer core rises, it starts the convection. The convection in the outer core, along with the rotation of Earth that causes rotation of the outer core, initiates a flow of electric current in the core. This flow of current within the core produces and sustains Earth’s magnetic field.

5. Why has the study of paleomagnetism and magnetic reversals been important in

understanding plate tectonics? (p. 39) Earth’s magnetic field is sufficient to permanently magnetize some surface rocks. For example, volcanic rock that erupts and cools at mid-oceanic ridges becomes magnetized at the time it passes through a critical temperature. At that critical temperature, known as the Curie point, iron-bearing minerals (such as magnetite) in the volcanic rock orient themselves parallel to the magnetic field. This is a permanent magnetization known as thermoremnant magnetization. The term paleomagnetism refers to the study of the magnetism of rocks at the time their magnetic signature formed. It is used to determine the magnetic history of Earth. Marine geologists towed magnetometers, instruments that measure magnetic properties of rocks, from ships and completed magnetic surveys. The paleomagnetic record of the ocean floor is easy to read because of the fortuitous occurrence of the volcanic rock basalt (see Chapter 5) that is produced at spreading centers and forms the floors of the ocean basins of Earth. The rock is finegrained and contains sufficient iron-bearing minerals to produce a good magnetic record. The marine geologists’ discoveries were not expected. The rocks on the floor of the ocean were found to have irregularities in the magnetic field. These irregular magnetic patterns were called anomalies or perturbations of Earth’s magnetic field caused by local fields of magnetized rocks on the seafloor. The anomalies can be represented as stripes on maps. When mapped, the stripes form quasi-linear patterns parallel to oceanic ridges. The marine geologists found that their sequences of stripe width patterns matched the sequences established by land geologists for polarity reversals in land volcanic rocks. These magnetic anomalies on the sea floor added new evidence to support the theory of plate tectonics.

6. What are hot spots? (p. 40)


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Hot spots are characterized by volcanic centers resulting from hot materials produced deep in the mantle (a mantle plume), perhaps near the core–mantle boundary. The partly molten materials are hot and buoyant enough to move up through mantle and overlying moving tectonic plates. An example of a continental hot spot is the volcanic region of Yellowstone National Park. Hot spots are also found in both the Atlantic and Pacific Oceans. If the hot spot is anchored in the slow-moving deep mantle, then, as the plate moves over a hot spot, a chain of volcanoes is produced. Perhaps the best example of this type of hot spot is the line of volcanoes forming the Hawaiian-Emperor Chain in the Pacific Ocean. Along this chain, volcanic eruptions range in age from present-day activity on the big island of Hawai’i (in the southeast) to more than 78 million years ago near the northern end of the Emperor Chain.

7. What is the difference between ridge push and slab pull in the explanation of plate

motion? (p. 46) Ridge push is a gravitational push, like a gigantic landslide, away from the ridge crest toward the subduction zone (the lithosphere slides on the asthenosphere). Slab pull results when the lithospheric plate moves farther from the ridge and cools, gradually becoming denser than the asthenosphere beneath it. At a subduction zone, the plate sinks through lighter, hotter mantle below the lithosphere, and the weight of this descending plate pulls on the entire plate, resulting in slab pull. Of the two processes, slab pull is the more influential of the driving forces. Calculations of the expected gravitational effects suggest that ridge push is of relatively low importance compared with slab pull.

Answers to Critical Thinking Questions: 1. Assume that the supercontinent Pangaea (see Figure 2.18*) never broke up. Now

deduce how Earth processes, landforms, and environments might be different from how they are today with the continents spread all over the globe. Hint: Think about what the breakup of the continents did in terms of building mountain ranges and producing ocean basins that affect climate and so forth.

If Pangaea never broke up, Earth processes would continue to erode existing mountains with no new mountain building. The land would be nearly flat and covered with sediments from the erosion of the mountains. Ocean circulation


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would remain the way it was back then, giving a warmer temperate climate known to the dinosaurs and not the circulation patterns we have today which gave us the ice ages. Mass extinctions are mostly the results of plate tectonics. If the plate tectonic process stopped, then life would probably have only gradual changes rather than abrupt changes we see in the geologic time scale.

* Textbook question states Figure 2.17, however, it should read 2.18.

Suggested Activities 1. Compare population density map with hazardous regions. Different types of hazards:

coastal regions and regions that are within close proximity to fault zones and volcanoes.

2. Collect and discuss newspaper clippings of different hazards that occur around the

world on a daily basis. Additional Resources (media, film, articles, journals, web sites) Print Resources Dealing with Natural Hazards Abbott, P.L., 2012, Natural Disasters, 8th ed., McGraw Hill, Boston, 512 pp. Bryant, E.A., 1993, Natural Hazards, Cambridge University Press, Cambridge, 294 pp. Eldredge, N., 1998, Life in the Balance, Princeton University Press, Princeton, 224 pp. Erikson, J., 2001, Quakes, Eruptions, and Other Geologic Cataclysms, Revealing the

Earth’s Hazards, Facts on File Science Library, The Living Earth Series, New York, 310 pp.

Griggs, G.B., and Gilchrist, J.A., 1983, Geologic Hazards, Resources, and Environmental Planning, Belmont, CA, Wadsworth Publishing Co., 502 pp.

Keller, E.A., 2000, Environmental Geology, eighth ed., Prentice Hall, Englewood Cliffs, N.J., 562 pp.

Kusky, T.M., 2004, Encyclopedia of Earth Science, 528 pages, Facts on File, New York, ISBN 0816049734.

Kusky, T.M., 2003, Geological Hazards: A Sourcebook, an Oryx Book, Greenwood Press, Westport, Conn., 300 pp., ISBN 1-57356-469-9.


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Mackenzie, F.T., and Mackenzie, J.A., 1995, Our Changing Planet: An Introduction to Earth System Science and Global Environmental Change, Prentice Hall, Englewood Cliffs, N.J., 387 pp.

Murck, B.W., Skinner, B.J., and Porter, S.C., 1997, Dangerous Earth: An Introduction to Geologic Hazards, John Wiley and Sons, New York, 300 pp.

Skinner, B.J., and Porter, B.J., 1989, The Dynamic Earth: An Introduction to Physical Geology, John Wiley and Sons, New York, 541 pp.

Nonprint Sources Dealing with Natural Hazards http://edcwww.cr.usgs.gov/ EROS Data Center lists satellite images, land cover maps, elevation models, maps, and aerial photography useful for Natural Hazards Studies. NASA’s web site on Natural Hazards: http://earthobservatory.nasa.gov/NaturalHazards/ NASA’s Earth Observatory lists satellite images of natural hazards, including dust, smoke, fires, floods, severe storms, and volcanoes. USGS web site for Natural Hazards: http://www.usgs.gov/themes/hazard.html USGS activities in the hazards theme area deal with describing, documenting, and understanding natural hazards and their risks. The web page contains explanations of individual hazards, geographic distribution of hazards, and fact sheets on hazards. The site also has links describing USGS involvement in recent hazards. http://www.accuweather.com/blogs/weathermatrix/ WeatherMatrix is a worldwide organization of over 3000 amateur and professional weather enthusiasts—meteorologists, storm chasers and spotters, and weather observers from all parts of the globe. WeatherMatrix was formerly the Central Atlantic Storm Investigators (CASI). Has frequently updated news about weather-related disasters. http://www.colorado.edu/hazards/o/ This web site is the online version of the periodical, The Natural Hazards Observer. It contains features about various hazards and disasters. It also provides information of emergency management, research, politics, and education of natural disasters. Organizations Dealing with Natural Hazards Congressional Natural Hazards Work Group is a cooperative endeavor between a group of private and public organizations, whose goal is to develop a wider understanding within Congress of the value of reducing the risks and costs of natural disasters. The work group supports the effort of the Congressional Natural Hazards Caucus. Information on the Natural Hazards Caucus Work Group can be found at:


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http://www.agiweb.org/gap/workgroup/resources.html. Some of the lead organizations include the American Meteorological Society and University Corporation for Atmospheric Research (http://www2.ucar.edu) and the National Science Foundation (http//www.nsf.gov). Federal Emergency Management Agency FEMA 500 C Street SW Washington, D.C. 20472 202-646-4600 http://www.fema.gov FEMA is the nation’s premier agency that deals with emergency management and preparation, and issues warnings and evacuation orders when disasters appear imminent. FEMA maintains a web site that is updated at least daily and includes information on hurricanes, floods, fires, national flood insurance, and disaster prevention, preparation, and emergency management. Divided into national and regional sites. Also contains information on costs of disasters, maps, and directions on how to do business with FEMA. U.S. Geological Survey U.S. Department of the Interior 345 Middlefield Road Menlo Park, CA 94025 650-329-5042 Also, offices in Reston, VA, Denver, CO http://www.usgs.gov/ The USGS is responsible for making maps of many of the different types of hazards discussed in this book, including earthquake and volcano hazards, tsunami, floods, landslides, and radon. The USGS National Landslide Information Center web site is http://landslides.usgs.gov/html_files/nlicsun.html. National Oceanographic and Atmospheric Administration (NOAA) http://www.noaa.gov/ NOAA conducts research and gathers data about the global oceans, atmosphere, space, and sun, and applies this knowledge to science and service that touch lives of all Americans. NOAA’s mission is to describe and predict changes in Earth’s environment, and conserve and wisely manage the nation’s coastal and marine resources. NOAA’s strategy consists of seven interrelated strategic goals for environmental assessment, prediction, and stewardship. These include (1) advance short-term warnings and forecast services, (2) implement season to interannual climate forecasts, (3) assess and predict decadal to centennial change, (4) promote safe navigation, (5) build sustainable fisheries, (6) recover protected species, and (7) sustain healthy coastal ecosystems. NOAA runs a web site that includes links to current satellite images of weather hazards, issues warnings of current coastal hazards and disasters, and has an extensive historical and educational service.


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The National Hurricane Center, http://www.nhc.noaa.gov/, is a branch of NOAA, and posts regular updates of hurricane paths and hazards. The National Drought Mitigation Center http://www.drought.unl.edu/ The National Drought Mitigation Center helps people and institutions develop and implement measures to reduce societal vulnerability to drought. The NDMC, based at the University of Nebraska-Lincoln, stresses preparation and risk management rather than crisis management.


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Chapter 3 Earthquakes Learning Objectives Earthquakes are serious natural hazards that affect people across the globe, sometimes at long distances from where the quakes occur. They are especially dangerous because seismologists, the scientists who study earthquakes, cannot predict them in time for evacuations or other precautions. Your goals in reading this chapter should be to

• understand how scientists measure and compare earthquakes. • be familiar with processes that take place in an earthquake such as faulting,

tectonic creep, and seismic waves. • know which global regions are most at risk for earthquakes and why they are at

risk. • know and understand the effects of earthquakes such as shaking, ground

rupture, and liquefaction. • identify how earthquakes are linked to other natural hazards such as landslides,

fires, and tsunamis. • know the important natural service functions of earthquakes. • know how human beings interact with and affect the earthquake hazard. • understand how we can minimize seismic risk, and recognize adjustments we

can make to protect ourselves.

Chapter Outline 3. Earthquakes

3.1. Introduction to Earthquakes 3.1.1. Earthquake Magnitude 3.1.2. Earthquake Intensity

3.2. Earthquake Processes 3.2.1. Process of Faulting

3.2.1.1. Fault Types 3.2.2. Fault Activity 3.2.3. Tectonic Creep and Slow Earthquakes 3.2.4. Seismic Waves

3.3. Earthquake Shaking 3.3.1. Distance to the Epicenter 3.3.2. Depth of Focus 3.3.3. Direction of the Rupture


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3.3.4. Supershear 3.3.5. Local Geologic Conditions

3.4. The Earthquake Cycle 3.5. Geographic Regions at Risk from Earthquakes

3.5.1. Plate Boundary Earthquakes Survivor Story 3.1: Magnitude 8.8 Earthquake and Tsunami on the Coast of Chile 3.5.2. Intraplate Earthquakes

3.6. Effects of Earthquake and Linkages with Other Natural Hazards 3.6.1. Shaking and Ground Rupture 3.6.2. Liquefaction 3.6.3. Regional Changes in Land Elevation 3.6.4. Landslides 3.6.5. Fires 3.6.6. Disease

3.7. Natural Service Functions of Earthquakes 3.7.1. Groundwater and Energy Resources 3.7.2. Mineral Resources 3.7.3. Landform Development 3.7.4. Future Earthquake Hazard Reduction

3.8. Human Interaction with Earthquakes 3.8.1. Earthquakes Caused by Human Activity

3.8.1.1. Water Reservoirs 3.8.1.2. Deep Waste Disposal 3.8.1.3. Nuclear Explosion

3.9. Minimizing the Earthquake Hazard 3.9.1. The National Earthquake Hazard Reduction Program 3.9.2. Estimation of Seismic Risk 3.9.3. Short-Term Prediction A Closer Look 3.2: Paleoseismic Earthquake Hazard Evaluation Case Study 3.3: The Denali Fault Earthquake

3.9.3.1. Ground Deformation 3.9.3.2. Seismic Gaps 3.9.3.3. Geophysical and Geochemical Phenomena

3.9.4. The Future of Earthquake Prediction Professional Profile 3.4: Andrea Donnellan, Earthquake Forecaster 3.9.5. Earthquake Warning Systems

3.10. Perception of and Adjustment to the Earthquake Hazard 3.10.1. Perception of the Earthquake Hazard 3.10.2. Community Adjustments to the Earthquake Hazard

3.10.2.1. Location of Critical Facilities 3.10.2.2. Structural Protection 3.10.2.3. Education 3.10.2.4. Increased Insurance and Relief Measures

3.10.3. Personal Adjustments: Before, During, and After an Earthquake


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Chapter Summary Large earthquakes release a tremendous amount of energy. Seismologists measure this energy on a magnitude (M) scale. On this scale, an increase from one whole number to the next represents a 10-fold increase in the amount of shaking and a 32-fold increase in the amount of energy released. The USGS National Earthquake Information Center and seismic observatories rapidly calculate a preliminary magnitude for a large earthquake and later revise the number after further analysis.

After an earthquake, scientists determine the intensity of its effects on people and structures. Earthquake intensity varies with the severity of the shaking and is affected by proximity to the epicenter, the local geological environment, and the engineering of structures. Intensity is described on the qualitative Modified Mercalli scale using reports of people’s experience and property damage, or as Instrumental Intensity using a dense network of seismographs. Information on intensity helps focus emergency efforts on areas that have experienced the most intense shaking. Other measurements, such as the amount of ground acceleration, are needed to design structures that can withstand shaking in future quakes.

Earthquakes create new fractures or occur on existing fracture systems. A fault is formed where a quake has displaced the Earth along a fracture. Displacement can be mainly horizontal, as along a strike-slip fault, or mainly vertical, as on a dip-slip fault. On thrust faults, a common type of low angle, dip-slip fault, displacement is both upward and horizontal. Faults may reach Earth’s surface, creating a fault scarp, or may remain buried as a blind fault.

A fault is usually considered to be active if it has moved during the past 10,000 years and potentially active if it has moved during the past 2 million years. Some faults exhibit tectonic creep, a slow displacement not accompanied by felt earthquakes.

Before an earthquake, strain builds up in the rocks on either side of a fault as the sides pull in different directions. When the stress exceeds the strength of the rocks, they rupture, and waves of energy, called seismic waves, radiate outward in all directions from the ruptured surface of the fault.

Seismic waves are vibrations that compress (P) or shear (S) the body of the Earth, or that travel across the ground as surface waves. Although P waves travel the fastest, it is the S and surface waves that cause most of the shaking and damage. The severity of the shaking of the ground and buildings is affected by the type and thickness of earth material present, the direction in which the fault ruptured, the depth of the earthquake focus, and for buildings, their engineering design.

Buildings highly subject to damage are those that (1) are constructed on unconsolidated sediment, artificially filled land, or water-saturated sediment, all of which tend to amplify shaking; (2) are not designed to withstand significant horizontal acceleration of the ground; or (3) have natural vibrational frequencies that match the frequencies of the seismic waves.


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Seismologists have proposed a four-stage earthquake cycle for large earthquakes. The first stage is a period of seismic inactivity, during which elastic strain builds up in rocks along a fault. The stage is followed by a stage of increased seismicity as the strain locally exceeds the strength of the rocks, initiating local faulting and small earthquakes. The third stage, which does not always occur, consists of foreshocks. Finally, the fourth stage is the mainshock, which occurs when the fault segment ruptures, producing the elastic rebound that generates seismic waves.

Most earthquakes occur on faults near tectonic plate boundaries, such as the San Andreas Fault in California, the Cascadia subduction zone in the Pacific Northwest, and the Aleutian subduction zone in Alaska. Intraplate earthquakes are also common in Hawaii, the western United States, the southern Appalachians and South Carolina, and the northeastern United States. Some of the largest historic earthquakes in North America occurred within the plate in the central Mississippi Valley in the early 1800s.

The primary effect of an earthquake is violent ground motion accompanied by fracturing, which may shear or collapse large buildings, bridges, dams, tunnels, pipelines, levees, and other structures. Other effects include liquefaction, regional subsidence, uplift of the land, landslides, fires, tsunamis, and disease. Earthquakes also provide natural service functions such as enhancing groundwater and energy resources, exposing or contributing to the formation of valuable minerals deposits, and, in some cases, potentially reducing the chance of future large quakes.

Human activity has locally increased earthquake activity by fracturing rock and

increasing water pressure underground below large water reservoirs, by raising fluid pressure in faults and fractures through the deep-well disposal of liquid waste, and by setting off underground nuclear explosions. The accidental damage caused by the first two activities is regrettable, but understanding how we have caused earthquakes may eventually help us to control or stop large natural earthquakes.

Reduction of earthquake hazards requires detailed mapping of geologic faults, the cutting of trenches to determine earthquake frequency, and detailed mapping and analysis of earth materials sensitive to shaking. It also requires new methods for predicting, controlling, and adjusting to earthquakes. Adjustments include improving structural design to better withstand shaking, retrofitting existing structures, microzonation of areas of seismic risk, and updating and enforcing building codes.

Being able to predict the location, date, time, and magnitude of earthquakes has been a long-term goal of seismologists. Accomplishing this goal is many years away. To date, scientists have been able to make long- and intermediate-term forecasts of earthquakes using probabilistic methods, but not consistent, accurate short-term predictions. A potential problem of predicting earthquakes is that their pattern of occurrence is often variable, with clusters of events separated by longer periods of time with reduced earthquake activity.

Warning systems and earthquake prevention are not yet reliable alternatives to earthquake preparedness. A satellite and sensor-based tsunami warning system being deployed in the Pacific Ocean will improve tsunami preparedness in some coastal areas. More communities must develop emergency plans to respond to a predicted or unexpected catastrophic earthquake, especially in areas of seismic risk outside of


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California. Such plans should include earthquake education, disaster response, drills, and improved insurance coverage. At a personal level, individuals who live in or visit areas of seismic risk can learn how to “duck, cover, and hold on” before the next large earthquake. Preparation both reduces the earthquake hazard and eases recovery. Answers to Review Questions: 1. What is the difference between the epicenter and focus of an earthquake? (p. 54)

The epicenter is the place on the Earth’s surface above where the ruptured rocks broke to produce the earthquake. The focus is the point of initial breaking below the Earth’s surface and it is directly below the epicenter.

2. What does the moment magnitude measure? How is it related to the amount of

shaking and the amount of energy released by an earthquake? (p. 54)

The moment magnitude measures the size of an earthquake. It is an estimate of the area that ruptured along the fault plane during the earthquake, the amount of movement and slippage along the fault, and the rigidity of the rocks near the focus of the quake.

3. What is instrumental intensity? How is it related to a shake map? (p. 55)

Instrumental intensity is the density of the network of high quality seismograph stations which transmits direct measurements of ground motion as soon as the shaking stops. This data is used to produce a shake map.

4. Explain how faulting occurs. (p. 56)

Faulting occurs when one lithospheric plate moves past another plate, slowed by the friction along their boundaries, or, on a smaller scale, when one block of rock is sliding past or over another, the stress builds up until the rocks overcome friction and suddenly slide past each other, releasing energy as an earthquake.

5. How are active and potentially active faults defined? (p. 58) Active faults have moved within the past 10,000 years and potentially active faults have not moved in the past 10,000 years but have moved during the Pleistocene.

6. What is paleoseismicity? (p. 60)

Paleoseismicity is the prehistoric record of earthquakes.


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7. What is the difference in the rates of travel of P, S, and surface waves? How is this

difference important in locating earthquakes? (p. 61) P waves are primary waves and move at about 3.7 miles per second, while S waves are secondary waves which move at about 1.9 miles per second. These waves travel more slowly than either P or S waves. The difference is important in locating earthquakes because scientists use the difference between the time the S waves and P waves arrive to determine the distance the epicenter is from the seismograph. Surface waves form and move along the Earth’s surface when P and S waves reach the land surface.

8. How do seismologists locate earthquakes? (p. 62) Seismographs locate earthquakes by using the difference between arrival times of the S and P waves to calculate the distance from the earthquake, and drawing a circle around the station corresponding to that distance. If three seismic stations are used, the circles corresponding to the distance from the epicenter should all intersect at one unique location, that of the epicenter.

9. How does the depth of an earthquake’s focus relate to the shaking and damage? (p. 65)

The deeper the focus of an earthquake, the less shaking will occur at the surface and therefore, less damage.

10. What types of earth materials amplify seismic waves? How is this amplification

related to earthquake damage? (p. 67) Seismic waves are amplified through unconsolidated sediment or soil. They are further amplified through material with high water content. The greater the amplification, the greater is the potential for damage.

11. Explain the earthquake cycle and elastic rebound. (p. 68)

The earthquake cycle proposes that there is a drop in elastic strain after an earthquake and a reaccumulation of strain before the next event.

12. What are foreshocks and aftershocks? (p. 68) Foreshocks are small- to moderate-magnitude earthquakes that occur before the main event. An aftershock is a smaller earthquake that occurs anywhere from a few minutes to approximately a year following the main event.

13. Where are earthquakes most likely to occur in the world? In North America? (p. 68)


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Most earthquakes occur along the boundaries of tectonic plates. Small- to medium-sized earthquakes occur along the mid ocean ridges, larger earthquakes occur along subduction zones and transform margins. In North America, earthquakes are most likely to occur on the West Coast along the San Andreas Fault, and fewer in South Carolina and the Mississippi Valley along some intraplate fault zones.

14. List the major effects of earthquakes. (p. 74) Major effects of earthquakes are shaking and ground rupture, liquefaction, and regional changes in land elevation, landslides, fires, and disease.

15. How do plate boundary and intraplate earthquakes differ? (p. 74) Intraplate earthquakes happen away from the plate boundaries and plate boundary earthquakes happen along the plate boundary.

16. Why aren’t the largest earthquakes always the most damaging and most deadly? (p.

74) Sometimes large earthquakes occur in areas of low population and therefore do not have the chance to harm as many people as an earthquake near a city. Also, the time of day that an earthquake takes place can have an effect on the number of deaths as many people may work in large high-rise buildings, or frequent congested business centers during working hours, but may live in smaller, less densely populated suburbs. Note: This question makes for a good discussion item as, in recent years population growth being exponential, significant growth has taken place in areas where large earthquakes can occur. Thus, the potential for harm from large earthquakes has increased as well. What has been seen over time is an attempt by man to construct population centers with earthquakes in mind. But, poor countries, Haiti for example, have more widespread death and destruction resulting from a failure to plan or lack of resources to build to withstand earthquakes. Chile was better prepared and had better construction standards and thus less death and destruction. But, as more recent events show (Christchurch, New Zealand September 4, 2010 early Saturday morning, followed by February 22, 2011 mid-day and mid-week, where the larger quake caused no deaths, but the later smaller quake caused more than 180 deaths, and the Japan quake and tsunami of March 11, 2011 with widespread death and destruction), more research, planning, and work is needed to prevent significant damage, destruction, and death in the future.

17. What are the effects of earthquake-induced liquefaction? (p. 76)


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Some of the effects of liquefaction are building collapse, dam failure, surfacing of underground structures, eruption of sand volcanoes, and subsidence.

18. Why do disease outbreaks sometimes follow major earthquakes and other large natural disasters? (p. 78)

Disease outbreaks sometimes follow major earthquakes and other natural disasters because there may be a loss of sanitation and housing, contaminated water supplies, disruption of public health services, and the disturbance of the natural environment. Earthquakes also rupture sewer and water lines, causing water to become polluted by disease-causing organisms. In many cases, victims are not buried properly or quickly, leading to further disease.

19. How can earthquakes be beneficial? (p. 79)

Earthquakes can be beneficial because they may expose economically valuable minerals or may allow for better groundwater flow, including the surfacing of springs. They uplift mountain ranges, forming spectacular scenery.

20. How can humans cause earthquakes? (p. 79) Humans can cause earthquakes by loading Earth’s crust, by injecting liquid waste deep into the Earth, or by creating underground nuclear explosions, bomb blasts, or doing anything that causes the ground to shake (even driving or playing music can generate seismic waves).

21. What kinds of information are useful in assessing seismic risk? (p. 81) If at all possible, seismic risk can be assessed using precursory phenomena such as: patterns and frequency of earthquakes, such as foreshocks; deformation of the ground surface; seismic gaps along faults; and geophysical and geochemical changes in Earth.

22. What kinds of phenomena may be precursors for earthquakes? (p. 83) Micro-earthquakes, strange animal behavior, deformation of ground surface, seismic gaps along faults, and geophysical and geochemical changes within the Earth may all be signs of an earthquake.

23. What is the difference between an earthquake prediction and forecast? (pp. 81–82) A prediction relies on precursors such as the events listed in number 22, and a forecast refers to the ability to determine a seismic event months to centuries in advance.


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24. What kinds of adjustments can a community make to the earthquake hazard? (pp. 91–

93)

Communities may locate critical facilities in safer areas, use structural protection through establishment of building codes, offer education, or increase insurance and relief measures.

25. What is retrofitting? (p. 92)

Retrofitting is making engineering changes to existing structures to make them better able to withstand shaking from earthquakes.

Answers to Critical Thinking Questions: 1. You live in an area that has a significant earthquake hazard. Public officials, the news

media, and citizens are debating whether an earthquake warning system should be developed. Some people are worried that the false alarms will cause a lot of problems, and others point out that the response time may be very long. What are your views on this? Should public funds be used to finance an earthquake warning system, assuming such a system is feasible? What are potential implications if a warning system is not developed and a large earthquake results in damage that could have been partially avoided with a warning system in place?

The first thing to do is to identify potential areas of long-term earthquake problems. Construction of earthquake-safe buildings and an awareness of long-term predictions are necessary. As far as a true warning system is concerned, you cannot predict an earthquake within days, but you possibly could within hours or minutes. This time frame would not allow people to move out of the way of all danger, so there must be an immediate safety plan (where to go if there is an earthquake, how to position yourself, etc.) in effect as well. Therefore, I think that an earthquake warning system should be put into effect in concert with public education of an immediate safety plan, which should be financed by public officials. Trains, nuclear plants, and other facilities may have time to shut down if a warning system were in place, saving many lives. In fact, all hazard protection should be the government's responsibility, and this type of protection could save many lives.

2. You are considering buying a home on the California coast. You know that

earthquakes are common in the area. What questions would you want to ask before purchasing the home? For example, consider the effects of earthquakes, the relationship of shaking to earth material, and the age of the structure. What might you


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do to protect yourself (both financially and physically) if you did decide to buy the house?

You should first find out when the house was built. If it is an older house, have renovations been done to make it earthquake safe? If it is a newer house, was it built in accordance with the earthquake building code? Find out what type of soil and/or bedrock the house was built on. If an earthquake occurs, certain types of soil can turn mushy and fail—an event called liquefaction. To protect yourself after buying a house, you can purchase earthquake insurance and you can also secure certain items in your house to prevent any damage during an earthquake (such as securing bookcases, shelving units, and kitchen dishes/cabinets).

3. You are working for the Peace Corps in a developing country where most of the

homes are built out of unreinforced bricks. There has not been a large damaging earthquake in the area for several hundred years, but earlier there were several earthquakes that killed thousands of people. How would you present the earthquake hazard to the people living where you are working? What steps might be taken to reduce the hazard?

I would study the area and determine the frequency of earthquakes in the area; perhaps the last earthquake was a 10,000-year quake. After that I would determine the likelihood that these people would have to deal with another in their lifetime. If these people probably would not have to, then the benefits of more affordable housing are well worth the savings at this point in time. In this case the benefits outweigh the costs. However, if they are very likely to experience an earthquake, then I would suggest building homes out of more sturdy material or trying to convince people to move onto more stable ground.

Suggested Activities

1. Find a water-saturated clay-mud, and put it in a fish tank with model towns inside

(including building, poles, etc.). Shake the tank to mimic an earthquake, and watch the effects of liquefaction.

2. Watch some of the fantastic movies of live earthquake coverage, and discuss with the

class what it must have been like to be in these situations. 3. Discuss the ground acceleration in large earthquakes, and the effects for large

accelerations.


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Additional Resources (media, films, articles, journals, web sites) Print Resources Dealing with Earthquakes Bolt, B.A., 1999, Earthquakes, fourth ed., New York, W.H. Freeman, 366 pp. Boraiko, A.A., 1986, Earthquake in Mexico, National Geographic, 169, 654–675. California Division of Mines and Geology, 1990, The Loma Prieta (Santa Cruz

Mountains) Earthquake of October 17, 1989, Special Publication 104. Coburn, A., and Spence, R., 1992, Earthquake Protection, Chichester, England, Wiley. Earthquakes and Volcanoes, a bimonthly publication of the U.S. Geological Survey

aimed at providing current information on earthquakes and seismology, volcanoes, and related natural hazards of interest to both generalized and specialized readers. Available from “Earthquakes and Volcanoes, U.S. Geological Survey, Mail Stop 967, Federal Center, Denver, CO 80225, (phone) 303-273-8408; (fax) 303-273-8450.

Kendrick, T.D., 1956, The Lisbon Earthquake, London, Metheun. Kusky, T.M., 2007, Earthquakes and Plate Tectonics, Facts on File, Hazardous Earth Set. Kusky, T.M., 2007, Tsunamis, Facts on File, Hazardous Earth Set. Logorio, H., 1991, Earthquakes: An Architect’s Guide to Non-Structural Seismic

Hazards, New York, Wiley. Reiter, L., 1990, Earthquake Hazard Analysis, New York, Columbia University Press. Reilinger, R., Toksoz, N., McClusky, S., and Barka, A., 2000, 1999 Izmit, Turkey

earthquake was no surprise, GSA Today, v. 10, no. 1, 1–6. Richter, C.F., 1958, Elementary Seismology, San Francisco, W.H. Freeman, pp. 137–138. U.S. Geological Survey, 1966, The Alaska Earthquake, March 27, 1964. Geological

Survey Professional Papers 542-B (Effects on Communities–Whittier); 542-D (Effects on Communities–Homer), 542-E (Effects on Communities, Seward); 542-G (Effects on Communities–Various Communities); 543-A (Regional Effects; Slide-induced waves, seiching and ground fracturing at Kenai Lake), 543-1 (Regional Effects–Tectonics); 543-B, Regional Effects–Martin-Bering Rivers area), 543-F (Regional Effects Ground Breakage in the Cook Inlet area); 543-H ( Regional Effects–Erosion and Deposition on a Raised Beach, Montague Island); 543-J (Regional Effects; Shore Processes and Beach Morphology); 544-C (Effects on Hydrologic Regime–Outside Alaska); 544-D (Effects on Hydrologic Regime–Glaciers); 544-E (Effects on Hydrologic Regime–-Seismic Seiches); 545-A (Effects on Transportation and Utilities– Eklutna Power Project).

U.S. Geological Survey, 1989, Lesson Learned from the Loma Prieta Earthquake of October 17, 1989, Circular 1045.

U.S. Geological Survey, 1907, The San Francisco Earthquake and Fire of April 18, 1906, U.S. Geological Survey Bulletin 324, 170 pages. (A thorough description of the damage resulting from the earthquake and fire of 1906, including many black and white photographs and first-hand descriptions. Rare book.)

Verney, P., 1979, The Earthquake Handbook, Paddington Press, 224 pages. Wallace, R.E. (ed.), 1990, The San Andreas Fault System, California, U.S. Geological

Survey Professional Paper 1515.


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Nonprint Resources Dealing with Earthquakes Videos: Hidden Fury: The New Madrid Earthquake Zone, 1993, Bullfrog Films, 27 mins. The Day the Earth Shook, 1995, NOVA, 55 mins. The Earth Revealed–Earthquakes, 1992, Annenberg CPB Project, 30 mins. Killer Quake, 1994, NOVA/KCET-TV, 60 mins. Loma Prieta Earthquake, 1992, U.S. Geological Survey, 53 mins. When the Earth Quakes, 1990, National Geographic, 28 mins. Web Sites: http://earthquake.usgs.gov/monitoring/anss/ Advanced National Seismic System: Site describes the activities of the nationwide seismograph networks. National Earthquake Information Center - NEIC http://earthquake.usgs.gov/regional/neic/ USGS National Strong-Motion Project http://nsmp.wr.usgs.gov/ http://earthquake.usgs.gov/earthquakes/recenteqsww/ Site shows current earthquake activity as the earthquakes occur. http://www.eas.slu.edu/Earthquake_Center/earthquakecenter.html St. Louis University Earthquake Center, specializing in central USA earthquakes. http://earthquake.usgs.gov/learn/faq/ Answers to frequently asked questions about earthquakes. http://earthquake.usgs.gov/learn/ USGS Educational resources for earthquakes. http://tsunami.geo.ed.ac.uk/local-bin/quakes/mapscript/home.pl Shows maps of global distribution of earthquakes. http://www.iris.washington.edu/hq/ IRIS consortium (Incorporated Research Institutions for Seismology), data center for facts about recent earthquakes. http://mceer.buffalo.edu/about_MCEER/default.asp National Center for Earthquake Engineering Research


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http://www.abag.ca.gov/bayarea/eqmaps/eqhouse.html San Francisco Bay area earthquake hazard information. http://www.christchurchquakemap.co.nz/ Time-lapse map showing earthquakes in the Christchurch, New Zealand area, including the 7.1 of Sept 4, 2010 and the 6.3 of Feb 22, 2011. Organizations Dealing with Earthquakes U.S. Geological Survey National Earthquake Information Center Federal Center Box 25046, MS 967 Denver, CO, 80225-0046 303-273-8500 Boston College Weston Geophysical Observatory Department of Geology and Geophysics 381 Concord Road Weston, MA 02493-1340 phone: 617-552-8300, fax: 617-552-8388 e-mail: [email protected] California Institute of Technology Seismological Laboratories 1200 East California Boulevard Pasadena, California 91125 626-395-6811 http://www.gps.caltech.edu/seismo/ Saint Louis University Department of Earth and Atmospheric Sciences Earthquake Center Room 329 Macelwane Hall 3507 Laclede Ave. Saint Louis, Missouri 63103 phone: 314-977-3131, fax 314-977-3117 University of Utah Seismograph Stations 135 South 1460 East Room 705 WBB Salt Lake City, Utah 84112-0111 phone: 801-581-6274, fax: 801-585-5585


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http://www.quake.utah.edu/


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Chapter 4 Tsunamis Learning Objectives In this chapter we focus on one of Earth’s most destructive natural hazards—the tsunami. Sometimes incorrectly called tidal waves, these ocean waves are both fascinating in their behavior and awesome in their power. Tsunamis are common in some coastal regions and very rare in others. Although they have long been known to cause disasters and catastrophes, the hazard posed by tsunamis has generally been underestimated. For years scientists attempted to get public officials to expand tsunami warning systems to ocean basins outside the Pacific Ocean. It took the catastrophic deaths and devastation of the Indonesian Tsunami of 2004 for many governments and communities to take the tsunami hazard seriously. However, as often occurs after disasters and catastrophes, translating the increased hazard awareness into improved warning, preparedness, and mitigation is proceeding at an excruciatingly slow pace. This chapter will examine the natural tsunami process and assess the hazard that these waves pose to people. Your goals in reading this chapter will be to

• understand the process of tsunami formation and development. • understand the effects of tsunamis and the hazards they pose to coastal

regions. • know what geographic regions are at risk for tsunamis. • recognize the linkages between tsunamis and other natural hazards. • know what nations, communities, and individuals can do to minimize the

tsunami hazard.

Chapter Outline 4. Tsunamis

4.1. Introduction 4.1.1. How Do Earthquakes Cause a Tsunami? 4.1.2. How Do Landslides Cause a Tsunami?

4.2. Regions at Risk Survivor Story 4.1: Tsunami in the Lowest Country on Earth

4.3. Effects of Tsunamis and Linkages with Other Natural Hazards 4.4. Natural Service Functions of Tsunamis 4.5. Human Interactions with Tsunamis 4.6. Minimizing the Tsunami Hazard

4.6.1. Detection and Warning 4.6.2. Structural Control


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4.6.3. Tsunami Runup Maps 4.6.4. Land Use 4.6.5. Probability Analysis 4.6.6. Education 4.6.7. Tsunami-Ready Status

4.7. Perception and Personal Adjustment to Tsunami Hazard Professional Profile 4.2: Jose Borrero – Tsunami Scientist

Chapter Summary The 2004 tsunami in the Indian Ocean that claimed at least 230,000 lives was an international wake-up call that we are not yet prepared for the tsunami hazard. Of primary importance is to ensure we have a tsunami warning system available in the world’s major ocean basins. This warning system must be designed to reach both coastal residents and visitors. The system must be coupled with an effective education program so that people are more aware of the hazard. A tsunami is produced by the sudden vertical displacement of ocean water. There are several possible processes that can produce tsunamis, including underwater landslides, submarine volcanic eruptions, and impact of extraterrestrial objects. However, the major source of large, damaging tsunamis over the past few millennia has been giant earthquakes associated with the major subduction zones on Earth. These tsunamis have formed where geologic faulting ruptures the seafloor and displaces the overlying water. When this happens, both a distant and local tsunami may be produced. Distant tsunamis can travel thousands of kilometers across the ocean to strike a remote shoreline. On the other hand, a local tsunami heads toward a nearby coast and can strike with little advance warning. Effects of a tsunami are both primary and secondary. The primary effects are related to the powerful water from the tsunami runup that results in flooding and erosion. Virtually nothing can stand in the path of a large-magnitude tsunami. In 2004 Indonesia, huge concrete barriers were moved by the force of the waves. Secondary effects of a tsunami include a potential for water pollution, fires in urban areas, and disease to people surviving the event. Tsunamis are linked to other natural hazards. For example, they are obviously tightly linked to the earthquakes that cause them and thus their effects are often combined with the ground shaking, fires, and subsidence associated with the quakes. Tsunami waves also interact with coastal processes to change the coastline through erosion and deposition of sediment. Following an earthquake and tsunami, a coastal area may scarcely resemble what it was prior to the event. A number of strategies are available to minimize the tsunami hazard. These include detection and warning, structural control, construction of tsunami runup maps, land-use practices, probability analysis, education, and achieving tsunami ready status. Of these, the detection and warning system is of paramount importance. For distant


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tsunamis, we have the capability to detect them in open ocean and accurately estimate their arrival time to within a few minutes. For local tsunamis, it is more difficult to provide adequate warning as tsunami wave formation quickly follows an earthquake or earthquake-produced landslide. In this case, warning sirens can alert people that a tsunami may soon arrive. Without adequate education, watches and warnings are often ineffective because many people do not know how to recognize a tsunami or take appropriate action to save themselves and others. Through education, people can learn the natural warning signs of an approaching tsunami. This may include the earthquake shaking itself and withdrawal of seawater prior to the arrival of the large wave. People must understand that tsunamis come in a series of waves and that the second or third wave may be the largest. In addition, the water returning to the ocean following tsunami inundation can cause as much damage as the runup of the incoming water. Along coasts with great or significant tsunami hazard, most communities have not adequately prepared for this underestimated natural hazard. Adequate preparation includes improved perception of the hazard, development of ways to alert the public, preparation and implementation of a tsunami preparedness plan, and promotion of community awareness and education concerning the hazard.

Answers to Review Questions: 1. What is a tsunami? (p. 104)

A tsunami is a large wave produced by the sudden vertical displacement of ocean water.

2. How do natural processes cause a tsunami? What is the primary process? (p. 104)

Rapid uplift or subsidence typically related to an earthquake, underwater landslides, collapse of a volcano (in the ocean), a submarine volcanic explosion, or the impact of a large extraterrestrial object can all cause a tsunami. These events all suddenly displace large amounts of ocean water, which moves outward in long-wavelength deep-water waves.

3. What is the difference between a distant and local tsunami? (p. 105)

The initial wave caused by fault displacement is split into two waves. One wave—the distant tsunami—travels across the deep ocean at high speed to strike remote shorelines with very little loss of energy. The second wave is the local tsunami. It heads in the opposite direction toward the nearby land and usually arrives quickly following an earthquake.

4. What are the major effects of a tsunami? (p. 110)


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Primary effects are related to the inundation of the water and resulting in flooding and erosion. Much of the damage to both the landscape and human structures results from the tremendous amount of debris carried by the water as it moves inland and then back into the ocean. Immediately following the tsunami, fires may start from ruptured natural gas lines or from the ignition of flammable chemicals, water supplies may become polluted, and disease outbreaks may occur.

5. Explain the relationship between plate tectonics and tsunamis. (p. 106) Most large tsunamis are produced by fault ruptures along subduction zones at tectonic plate boundaries.

6. How are tsunamis detected in the open ocean? (p. 112)

A tsunami warning system consists of three components: (1) a network of seismographs can accurately locate and determine the depth and magnitude of submarine and coastal earthquakes; (2) automated tidal gauges measure unusual rises and falls of sea level; and (3) a network of sensors connected to floating buoys with bottom sensors, known as tsunameters, detect small changes in the pressure exerted by the increased volume of water as a tsunami passes overhead. This information is relayed by satellite to a warning center and is combined with tidal gauge information to predict tsunami arrival times.

7. What is the difference between a tsunami watch and tsunami warning? (p. 115)

A tsunami watch is a notification that an earthquake that can cause a tsunami has occurred, while a tsunami warning is notification that a tsunami has been detected and is spreading across the ocean toward an area.

8. What are the primary and secondary effects of tsunamis? (p. 110)

Primary effects of tsunamis include the destruction caused by the waves rushing into and out of shoreline areas. Secondary effects are those that come later, such as disease, loss of productivity of the land from seawater evaporation leaving salts behind, and loss of economic bases for area.

9. Describe the methods used to minimize the tsunami hazard. (p. 111)

Strategies that minimize the tsunami hazard include detection and warning, structural control, construction of tsunami runup maps, land-use practices, probability analysis, education, and achieving tsunami ready status.


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10. What is meant by tsunami-ready status? (p. 116)

For a community to be tsunami ready, it must establish an emergency operation center with 24-hour capability, have ways to receive information from monitoring agencies, have ways to alert the public, develop a tsunami preparedness plan with emergency drills, and promote community awareness programs to educate the public.

Answers to Critical Thinking Questions: 1. You are placed in charge of developing an education program with the objective of

raising a community’s understanding of tsunami. What sort of program would you develop and what would it be based upon?

Very effective teaching methods can be achieved by showing videos of the 2004 Indian Ocean tsunami, then discussing the warning signs of tsunami, discuss what to do when a tsunami is suspected, and teach people to know evacuation routes. It is most important that people understand that tsunamis travel in groups of waves, and that after the first wave passes, many more may be coming spaced 45 minutes to several hours apart.

2. What do you think the role of the media should be in helping make people more

aware of the tsunami hazard? How should scientists be involved in increasing the perception of this hazard?

The media should report of the work of scientists who are determining the tsunami risk for coastal populations. Scientists should prepare learning modules for local coastal communities, and help in determining the safest escape routes.

3. You live on a coastal area that is subject to large, but infrequent, tsunamis. You are

working with the planning department of the community to develop tsunami ready status. What issues do you think are most important in obtaining this status and how could you convince the community that it is necessary or in their best interest to develop tsunami ready status?

It will be important to have warning systems in place, to have clearly marked evacuation routes, and for the population to understand the threats of multiple waves. Safe areas with supplies of food, water, and medicine should be


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located in high areas, and backup means of communication should be ready for emergency. A system for neighbors to check on neighbors after the event should be established.

Additional Resources (media, films, articles, journals, web sites)

Print Resources Dealing with Tsunamis Bernard, E. N., ed., 1991, Tsunami Hazard: A Practical Guide for Tsunami Hazard

Reduction. Dordrecht, The Netherlands: Kluwer Academic Publishers. Booth, J. S., O’Leary, D. W., Popencoe, P., and Danforth, W. W., 1993, US Atlantic

Continental Slope Landslides: Their Distribution, General Attributes, and Implications, U.S. Geological Survey Bulletin 2002, 14–22.

Dawson, A. G., and Shi, S., 2000, Tsunami deposits, Pure and Applied Geophysics 157, 493–511.

Driscoll, N. W., Weissel, J. K., and Goff, J. A., 2000, “Potential for large-scale submarine slope failure and tsunami generation along the U.S. Mid-Atlantic Coast,” Geology, 28, 407–10.

Dvorak, J., and Peek, T., 1993, Swept away, Earth, v. 2, no. 4, 52–59. Kusky, T.M., 2007, Tsunami, Facts on File, Hazardous Earth Set. Latter, J. H., 1981, Tsunami of Volcanic Origin, Summary of Causes, with Particular

Reference to Krakatau, 1883, Journal of Volcanology 44, 467–90. McCoy, F., and Heiken, G., 2000, Tsunami generated by the late Bronze Age eruption of

Thera (Santorini), Greece, Pure and Applied Geophysics 157, 1227–56. Minoura, K., Inamura, F., Nakamura, T., Papadopoulos, A., Takahashi, T., and Yalciner,

A., 2000, Discovery of Minoan tsunami deposits, Geology 28, 59–62. Minoura, K., Inamura, F., Takahashi, T., and Shuto, N., 1997, Sequence of sedimentation

processes caused by the 1992 Flores Tsunami, evidence from Babi Island, Geology 25, 523–26.

Okazaki, S., Shibata, K., and Shuto, N., 1995, A Road Management Approach for Tsunami Disaster Planning, in Y. Tsuchiya and N. Shuto, eds., Tsunami: Progress in Prediction Disaster Prevention and Warning. Boston: Kluwer Academic Publishers, pp. 223–34.

Revkin, A. C., 2000, “Tidal waves walled threat to East Coast,” New York Times, July 14, sec. A18.

Satake, K., 1992, Tsunamis, Encyclopedia of Earth System Science 4, 1992, 389–97. Steinbrugge, K. V. Earthquakes, Volcanoes, and Tsunamis: An Anatomy of Hazards.

New York: Skandia America Group, 1982. Tsuchiya, Y., and Shuto, N., eds., 1995, Tsunami: Progress in Prediction Disaster

Prevention and Warning, Boston: Kluwer Academic Publishers, 336 pp.


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U.S. Geological Survey, 1987, Surviving a Tsunami—Lesson from Chile, Hawaii, and Japan, U.S. Geological Survey Circular 1187.

Yeh, H., Imamura, F., Syndakis, C., Tsuji, Y., Liu, P., and Shi, S., 1993, The Flores Island Tsunami, Transactions of the American Geophysical Union, N33.

Nonprint Resources Dealing with Tsunamis The following web sites offer tsunami information: http://www.ngdc.noaa.gov/hazard/tsu.shtml http://walrus.wr.usgs.gov/tsunami http://www.pmel.noaa.gov/tsunami http://www.tsunami.noaa.gov/education.html http://www.oesd.noaa.gov/TERK/terk_intro.htm http://www.conservation.ca.gov/cgs/geologic_hazards/Tsunami/Pages/education.aspx http://www.aktsunami.com/ Tsunami Warning information: http://ptwc.weather.gov/ http://wcatwc.arh.noaa.gov/ Organizations Dealing with Tsunamis National Tsunami Hazard Mitigation Program This partnership between the states of Hawaii, Alaska, California, Oregon, and Washington and the Federal Emergency Management Agency, National Oceanic and Atmospheric Administration, and U.S. Geological Survey is preparing maps showing tsunami inundation areas and implementing mitigation plans for the states in the program. The NTHMP is also developing an early warning system, including seismic stations and deep ocean tsunami detectors. U.S. Geological Survey 345 Middlefield Road Menlo Park, CA 94025 650-329-5042 Tsunami Research Center (USC) Biegler Hall, University of Southern California Los Angeles, California 90089-2531


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213-740-5129 http://www.usc.edu/dept/tsunamis/2005/index.php NOAA Center for Tsunami Research NOAA/PMEL/OE2 7600 Sand Point Way NE Seattle, WA 98115


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Chapter 5 Volcanoes Learning Objectives There are about 1500 active volcanoes on Earth, almost 400 of which have erupted in the last century. While you are reading this paragraph, at least 20 volcanoes are erupting on our planet. Volcanoes occur on all seven continents as well as in the middle of the ocean. When human beings live in the path of an active volcano, the results can be devastating. Your goals in reading this chapter should be to

• know the different types of volcanoes and their associated features. • understand the relationship of volcanoes to plate tectonics. • know what geographic regions are at risk from volcanoes. • know the effects of volcanoes and their linkages to other natural hazards. • recognize the potential benefits of volcanic eruptions. • understand how we can minimize the volcanic hazard. • know what adjustments we can make to avoid death and damage from

volcanoes.

Chapter Outline 5. Volcanoes

5.1. Introduction to Volcanoes 5.1.1. How Magma Forms 5.1.2. Magma Properties

5.1.2.1. Viscosity 5.1.2.2. Volatile Content of Eruptive Behavior

5.1.3. Volcano Types 5.1.3.1. Shield Volcanoes 5.1.3.2. Composite Volcanoes 5.1.3.3. Volcanic Domes 5.1.3.4. Cinder Cones

5.1.4. Volcanic Features 5.1.4.1. Craters, Calderas, and Vents 5.1.4.2. Hot Springs and Geysers 5.1.4.3. Caldera Eruptions

5.1.5. Volcano Origins 5.2. Geographic Regions at Risk for Volcanoes 5.3. Effects of Volcanoes

5.3.1. Lava Flows 5.3.2. Pyroclastic Activity


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5.3.2.1. Pyroclastic Flows 5.3.2.2. Ash Falls

5.3.3. Poisonous Gases 5.3.4. Debris Flows, Mudflows, and Other Mass Movements

5.3.4.1. Debris Flows 5.3.4.2. Mudflows 5.3.4.3. Landslides Case Study 5.1: Volcanic Landslides and Tsunamis

5.3.5. Mount St. Helens 1980–2010: From Lateral Blasts to Lava Flows 5.4. Linkages between Volcanoes and Other Natural Hazards 5.5. Natural Service Functions of Volcanoes

5.5.1. Volcanic Soils 5.5.2. Geothermal Power 5.5.3. Mineral Resources 5.5.4. Recreation 5.5.5. Creation of New Land

5.6. Human Interaction with Volcanoes 5.7. Minimizing the Volcanic Hazard

5.7.1. Forecasting 5.7.1.1. Seismic Activity 5.7.1.2. Thermal, Magnetic, and Hydrologic Monitoring 5.7.1.3. Land Surface Monitoring 5.7.1.4. Monitoring Volcanic Gas Emissions 5.7.1.5. Geologic History

5.7.2. Volcanic Alert or Warning Professional Profile 5.2: Chris Eisinger, Studying Active Volcanoes

5.8. Perception of and Adjustment to the Volcanic Hazard 5.8.1. Perception of Volcanic Hazard

Survivor Story 5.3: A Close Call with Mount St. Helens 5.8.2. Adjustment of Volcanic Hazards 5.8.3. Attempts to Control Lava Flows

Chapter Summary Lava is a magma that has been extruded from a volcano. Its viscosity, a characteristic related to the temperature and silica content, and gas content are important in determining the eruptive style of the different types of volcanoes. The largest volcanoes, shield volcanoes, are common at mid-ocean ridges, such as Iceland, and over mid-plate hot spots, such as the Hawaiian Islands. They are characterized by nonexplosive lava flows of basalt. Most volcanic eruptions are from classic, cone-shaped composite volcanoes that occur above subduction zones, particularly around the Pacific Rim. Many of the volcanoes in the Aleutian Islands of Alaska and the Cascade Mountains of the U.S. Pacific Northwest are of this type. These volcanoes are characterized by explosive eruptions and are composed of silica-rich lavas, such as andesite, and pyroclastic


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deposits. Volcanic domes are generally smaller, sometimes highly explosive volcanoes that occur inland of subduction zones. They include Lassen Peak in California and are composed largely of rhyolite rock.

Features of volcanoes include vents, craters, and calderas. Other features related to volcanic activity are hot springs and geysers. Large calderas are created by infrequent, huge violent eruptions. Following an explosive beginning, they often resurge and may present a volcanic hazard for a million years or longer. Recent uplift and earthquakes at the Long Valley caldera in eastern California are reminders of the potential hazard.

Volcanic activity is directly related to plate tectonics. Most volcanoes are located at plate boundaries, where magma is produced in the spreading or sinking of lithospheric plates. Two-thirds of the world’s volcanoes are associated with the sinking of lithospheric plates along the “Ring of Fire” surrounding most of the Pacific Ocean. Specific geographic regions of North America at risk from volcanoes include the northwest coast of California, Oregon, Washington, and parts of British Columbia and Alaska, Long Valley, and the Yellowstone National Park area.

Primary effects of volcanic activity include lava flows, pyroclastic hazards, and occasionally the emission of poisonous gases. Hydraulic chilling and the construction of walls have been used in attempts to control lava flows. These methods have had mixed success and require further evaluation. Pyroclastic hazards include volcanic ash falls, which may cover large areas with carpets of ash; pyroclastic flows that move as fast as 160km (100mi) per hour down the side of a volcano; and lateral blasts, which can be very destructive. Secondary effects of volcanic activity include debris flows and mudflows, generated when melting snow and ice or precipitation mix with volcanic ash. These flows can devastate an area many kilometers from the volcano. All these effects have occurred in recent history of the Cascade Range of the Pacific Northwest and will occur there in the future.

Volcanoes are linked to other natural hazards such as fire, earthquakes, landslides, and climate change. However, they also provide us with natural service functions: fertile soils, a source of power, mineral resources, recreational opportunities, and newly created land.

Efforts to meet the goal of reducing volcanic hazards are focusing on human and societal issues of communication; the objective is to prevent a volcanic crisis from become a disaster or catastrophe. Sufficient monitoring of seismic activity; thermal, magnetic, and hydrologic properties; and changes in the land surface, combined with knowledge of the recent geologic history of volcanoes, may eventually result in reliable forecasting of volcanic activity. Forecasts of eruptions have been successful, particularly for Hawaiian volcanoes and Mt. Pinatubo in the Philippines. Worldwide, however, it is unlikely that we will be able to accurately forecast most volcanic activity in the near future.

The U.S. Geological Survey has developed an alert notification system for volcanic activity that has four levels for hazards on land and four color codes for aviation hazards. Hard questions remain concerning when evacuation should begin and when it is safe for people to return.

Perception of the volcanic hazard is apparently a function of age and length of residency near the hazard. Some people have little choice but to live near a volcano.


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Community-based education plays an important role in informing people about the hazards of volcanoes. Apart from psychological adjustment to losses, the primary human adjustment to volcanic activity is evacuation. Some attempts to control lava flows once an eruption has begun have been successful.

Answers to Review Questions: 1. What is magma and where does it come from? (p. 126)

Magma is very thick underground liquid derived from melted rock material that contains small but significant amounts of dissolved gas, mostly water vapor and dissolved carbon dioxide. Most magmas come from the asthenosphere, the weak layer that underlies the lithospheric plates.

2. What physical and chemical changes occur that cause rocks to melt? (p. 126)

The three principle ways in which silicate rocks can melt: (1) decompression, (2) addition of volatiles (e.g., dissolved gas), and (3) addition of heat.

3. What is viscosity, and what determines it? (p. 126)

Viscosity is the measure of resistance to flow in fluids (it is the opposite of fluidity). Viscosity is determined by both silica content (as silica content increases viscosity increases) and temperature (as temperature increases viscosity decreases).

4. Explain the relationship between magma composition, viscosity, and gas content. (pp.

126–128)

Silicic magmas have longer chains of silicate minerals and are more viscous than mafic magmas. Silicic magmas also tend to have more dissolved gases in them than mafic magmas and are more explosive when they erupt.

5. List the major types of volcanoes and the type of magma associated with each. (pp.

128–131)

Major Types of Volcanoes Magma

Shield Volcano Basaltic Magma Composite Volcano (Stratavolcano) Andesitic Magma Volcanic Domes Rhyolite Magma Cinder Cones Basaltic Magma


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6. Describe the major types of volcanoes and their eruption styles. Why do they erupt the way they do? (pp. 128–131)

Shield volcanoes form from relatively nonexplosive lavas due to their low silica content and low dissolved gas content. However, shield volcanoes can produce tephra, which is explosively ejected material. Composite volcanoes, also called stratovolcanoes, are composed of both pyroclastic debris and less explosive lava flows. If one could cut these volcanoes in half from top to bottom, the alternating types of flow create a striped effect. Volcanic domes form from highly explosive eruptions, when highly viscous magma rises to slowly fill the volcanic vent after a major eruption. These are explosive because they are highly viscous and have large amounts of dissolved gas. Cinder cones form by the accumulation of tephra around a volcanic vent. Hot-spot oceanic basaltic volcanoes typically form shield volcanoes, or smaller volcanoes known as seamounts and guyots. These have little dissolved gases and are not particularly explosive. Hot-spot continental rhyolitic magma forms large caldera complexes, such as Yellowstone caldera. These may accumulate large amounts of dissolved gases and produce tremendously explosive and powerful eruptions.

7. Explain the relationship between plate tectonics and volcanoes. (pp. 134–137)

Tectonic setting determines the type of volcano. Mid-ocean ridges produce lava plains. Subduction zones produce composite volcanoes. Hot spots beneath oceans produce basaltic shield volcanoes, while hot spots beneath continents produce caldera-forming eruptions and rhyolitic magma.

8. How do lava tubes form and move magma far from the erupting vents? (p. 130)

Lava tubes help move magma far from the erupting vents because the tubes insulate the magma, preventing a drop in temperature which would cause solidification of the magma closer to the eruption site.

9. Explain the relationship between the Hawaiian Islands and the hot spot below the big

island of Hawaii. (p. 137)

The hot spot below Hawaii is responsible for creating the entire island chain. The hot spot appears to have been stationary for millions of years while the


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Pacific plate was moving over the hotspot and toward the northwest. As the plate moved, the hot spot essentially burned a hole in the overriding plate, erupting a series of volcanoes that are older to the northwest, and ending with the currently active calderas on Hawaii. The period of time that the hot spot has been active is the period of time in which the Hawaiian Islands formed. Currently, another “island” to the southeast of the big island of Hawaii is beginning to form.

10. How do geysers work? How can they be hazardous? (pp. 132–134)

Geysers originate when groundwater comes into contact with hot rock in an underground thermal chamber. As the water gets closer to the hot rock, the water begins to boil, producing sporadic or episodic stream-driven releases of water and steam. Geysers can be unpredictable and as the caldera in which they form remains active there is a potential hazard from future volcanic eruptions.

11. Explain how large caldera eruptions occur and why they are so dangerous. (p. 133)

Caldera eruptions are dangerous because they are formed during explosive ejections of magma. Calderas contain volcanic vents that spew forth lava and pyroclastic debris in huge quantities. Some caldera eruptions have changed global climate for years.

12. Describe the primary and secondary effects of volcanic eruptions. (p. 138)

Primary effects of volcanic eruptions are direct results of the explosion. These effects include lava flow; pyroclastic activity, such as ash fall, pyroclastic flows, and lateral blasts; and the release of volcanic gases. The primary effects cause secondary effects of volcanic eruptions. These effects include debris flow, mudflows, landslides, debris avalanches, floods, fires, tsunami, atmospheric changes, loss of crop productivity, disease, and displacement of populations.

13. What methods have been attempted to control lava flow? (pp. 158–159)

Some methods which have been attempted to control lava flow include bombing, hydraulic chilling with fire hoses, and wall construction.

14. Differentiate between ash falls, lateral blasts, and pyroclastic flows. (p. 141)

Ash falls are fine-grained rock and volcanic glass fragments and gas blown high into the air by volcanic explosions that settle back to earth.


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Lateral blasts happen when an explosion destroys part of the volcanoes as gas, ash, and rock fragments are blown horizontally from the sides of the mountain. The eruption of Mount St. Helens in 1980 involved a lateral blast. The eruptions move at high speeds and can be very destructive. Ash flows, also known as nueé ardentes, are avalanches of very hot pyroclastic material blown out of a vent moving rapidly down the side of the volcanoes.

15. What are the major gases emitted in a volcanic eruptions? How can they be

hazardous? (p. 142)

The major gases emitted during a volcanic eruption are water vapor, carbon dioxide, carbon monoxide, sulfur dioxide, and hydrogen sulfide. The most dangerous gases include carbon dioxide, sulfur dioxide, and hydrogen sulfide.

16. Explain how volcanoes can produce gigantic debris or mudflows. (pp. 143–144)

Mudflows, or lahars, are produced when large amounts of loose volcanic ash and other tephra are saturated with water and become unstable, causing the mass to slide downslope. In some cases, volcanic eruptions cause glaciers to melt, suddenly adding huge quantities of water to the slope.

17. What kinds of information help geologists forecast volcanic eruptions? (p. 152)

Some possible methods for forecasting volcanic eruptions are monitoring seismic activity; monitoring thermal, magnetic, and hydraulic conditions; monitoring the land surface to detect tilting of swelling of the volcano; monitoring of volcanic gas emissions; and studying the geologic history of a particular volcano or volcanic center.

18. Explain the USGS alert notification system for volcanic eruptions. (p. 155) This system has two components: ground-based volcanic alert levels and aviation-based color code levels. Each component has four levels and for most monitored volcanoes and eruptions, the alert and aviation code will be at the same level. For some eruptions, the hazard posed to either those on the ground or in the air will differ.

Answers to Critical Thinking Questions:


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1. While looking through some old boxes in your grandparents’ home, you find a sample of volcanic rock collected by your great-grandfather. No one knows where it was collected. You take it to school, and your geology professor tells you that it is a sample of andesite. What might you tell your grandparents about the type of volcano from which it probably came, its geologic environment, and the type of volcanic activity that likely produced it?

The sample of andesite probably came from a composite volcano located above a subduction zone. It was likely produced when rising magma mixed with both oceanic and continental crust. Due to the fact that continental crust has higher silica content than basalt, andesite (a composite volcanic rock) has intermediate silica content.

2. In our discussion of adjustment and perception to volcanic hazards, we establish that

people’s perceptions and what they will do in case of an eruption are associated with both their proximity to the hazard and their knowledge of volcanic processes and necessary adjustments. With this association in mind, develop a public relations program that could alert people to a potential volcanic hazard. Keep in mind that the tragedy associated with the eruption of Nevado del Ruiz was in part due to political and economic factors that influenced the apathetic attitude toward the hazard map prepared for that area. Some people were afraid that the hazard map would result in lower property values in high-risk areas.

A public relations program would need to cover two concepts in detail. The first goal would be to promote living a safe distance away from the volcano. If this does not work, as most geological guidelines go unheard until disaster breaks, the next task would be to attempt to increase the knowledge base of the public. For example guidelines my inform people that living on the flank of an active or potentially active volcano is dangerous and could result in loss of material items or life. Other important information is to teach primary and secondary effects of eruptions. If the people do not move out on their own it is essential for them to be aware of current evacuation procedures, and it is also essential for government officials to understand how they might be able to attempt to change lava flow and mudflow directions away from population centers.

3. You are going to take a scout trip to Hawaii to see Kilauea volcano. Some children

have seen documentaries of the 1980 eruption of Mount St. Helens and are afraid; others are fearless and want to try cooking on a lava flow. What will you tell the fearful scouts? Describe the safety precautions you will follow for all the scouts.

First, tell them to trust the teacher. Then explain the differences between gases dissolved in soda and gases dissolved in water. Take a can of both, shake them, and tell them the soda is like Mt. St. Helens and the water is like


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Hawaii. Ask them which is safer. Then tell all the scouts that even though Hawaii will not have huge explosive eruptions, it can have small explosions, and the magma is more than 1,000 ºC hot. Many people have died by walking across cool crusts of lava that were thin, and fallen through to a hot fiery death. Tell them to trust the teacher and not go off the trail.

Suggested Activities 1. If possible, visit an active or dormant volcano in your area, and discuss where lava

flows might go, where and how far mudflows might go, and discuss the rates of nueé ardentes flows.

2. Divide the class into two groups, one advocating raising volcanic alert levels after a

swarm of microearthquakes, and one advocating not causing fear and potential loss of a harvest by evacuating local farmers for what could be a couple of month wait for an eruption that might or might not occur. Discuss the Mount Pinatubo example.

Additional Resources (media, films, articles, journals, web sites) Print Resources Dealing with Volcanic Eruptions Fisher, R.V., 2000, Out of the Crater: Chronicles of a Volcanologist, Princeton,

Princeton University Press, 180 pp. Fisher, R.V., Heiken, G., and Hulen, J.B., 1998, Volcanoes: Crucibles of Change,

Princeton, Princeton University Press, 334 pp. Holloway, M., 2001, Trying to tame the roar of deadly lakes, New York Times, Science

Tuesday, Feb. 27, p. D3. Kusky, T.M., 2007, Volcanoes and Volcanic Eruptions, Facts on File, Hazardous Earth

Set. Lacey, M., 2002, Tens of thousands flee a devastating volcano in Congo, New York

Times, Jan 19, 2002, p. A3. Simkin, T., and Fiske, R.S., 1993, Krakatau 1883: The Volcanic Eruption and Its Effects,

Washington, D.C., Smithsonian Institution Press. Nonprint Resources Dealing with Volcanic Eruptions


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http://volcano.oregonstate.edu/ VolcanoWorld. Presents updated information about eruptions, volcanoes, and has many interactive pages designed for different grade levels from kindergarten through college and professional levels.

http://volcanoes.usgs.gov/

US Geological Survey Volcano Hazards Program. Contains updates of U.S. and worldwide volcanic activity, and has feature articles on recent research. Also has links to sites on volcanic hazards, historical eruptions, monitoring programs, emergency planning, and warning schemes. Has resources including photos, fact sheets, videos, and an education page. Also offers grants to college students doing volcano research.

http://vulcan.wr.usgs.gov/

Cascade Volcano Observatory. Contains information and news on the volcanoes that make up the Cascade Range of the Pacific Northwest. Provides links to information regarding specific areas and volcanoes.

http://hvo.wr.usgs.gov/

Hawaiian Volcano Observatory. Site includes updates of current volcanic activity.

http://pubs.usgs.gov/fs/2000/fs152-00/ Viewing Lava Safely—Common Sense Is Not Enough. Jenda Johnson. A short guide to some of the volcanic hazards associated with viewing lava flows on Kilauea Volcano, Hawaii.

http://pubs.usgs.gov/fs/fs169-97/

Volcanic Air Pollution—A Hazard in Hawai’i. Jeff Sutton, Tamar Elias, James Hendley II, and Peter Stauffer. Discussion of the various gases and pollution produced by Kilauea volcano, Hawaii.


Living on Active Volcanoes—The Island of Hawai’i. Discussion of the volcanic activity and hazards on the island of Hawaii. Includes maps showing areas of low through high risk for volcanic hazards.

http://pubs.usgs.gov/fs/2000/fs060-00/

Mount Hood—History and Hazards of Oregon’s Most Recently Active Volcano. Cynthia Gardner, William Scott, Jon Major, and Thomas Pierson. Discussion of historical activity of Mount Hood, and possible hazards to Portland, Oregon and vicinity. Includes maps of proximal and distal hazard areas.



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(May 2000). Mount Baker—Living with an Active Volcano. Kevin Scott, Wes Hildreth, and Cynthia Gardner. Discussion of hazards associated with Mount Baker, and discussions of why certain areas have been closed to tourists.


Mount St. Helens—From the 1980 Eruption to 2000. Steve Brantley and Bobbie Myers. History of Mount St. Helens Eruptions.


Chris Newhall, Peter H. Stauffer, and James W. Hendley II—Lahars of Mount Pinatubo, Philippines—On June 15, 1991, Mount Pinatubo in the Philippines exploded in the second largest volcanic eruption on Earth this century. This eruption deposited more than 1 cubic mile (5 cubic kilometers) of volcanic ash and rock fragments on the volcano’s slopes. Within hours, heavy rains began to wash this material down into the surrounding lowlands in giant, fast-moving mudflows called lahars. In the next four rainy seasons, lahars carried about half of the deposits off the volcano, causing even more destruction in the lowlands than the eruption itself.


David Hill, Roy Bailey, Michael Sorey, James Hendley II, and Peter Stauffer. Living with a Restless Caldera—Long Valley, California. Description of the rising magma beneath Long Valley, California, and the volcanic hazards this poses to the western U.S. Includes accounts of historical eruptions, and system of warnings that are in place in the event of an eruption.


Living on Active Volcanoes—The Island of Hawai’i — People on the Island of Hawai’i face many hazards that come with living on or near active volcanoes. These include lava flows, explosive eruptions, volcanic smog, damaging earthquakes, and tsunamis (giant seawaves). As the population of the island grows, the task of reducing the risk from volcano hazards becomes increasingly difficult. To help protect lives and property, U.S. Geological Survey (USGS) scientists at the Hawaiian Volcano Observatory closely monitor and study Hawai’i’s volcanoes and issue timely warnings of hazardous activity.


Volcanic Ash–Danger to Aircraft in the North Pacific — The world’s busy air traffic corridors pass over hundreds of volcanoes capable of sudden, explosive eruptions. In the United States alone, aircraft carry many thousands of passengers and millions of dollars of cargo over volcanoes each day. Volcanic ash can be a serious hazard to aviation even thousands of miles from an eruption. Airborne ash can diminish visibility, damage flight control systems, and cause jet engines to fail. USGS and other scientists with the Alaska Volcano Observatory are playing a leading role in the international effort to reduce the risk posed to aircraft by volcanic eruptions.


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The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines. Chris Newhall, James Hendley II, and Peter Stauffer. Detailed descriptions of the huge eruption of Mount Pinatubo in 1991. Also includes assessment of continuing hazards.

Organizations Dealing with Volcanoes Cascades Volcano Observatory U.S. Geological Survey 5400 MacArthur Blvd. Vancouver, WA 98661 360-993-8900 Alaska Volcano Observatory United State Geological Survey 4200 University Drive Anchorage, Alaska 99508 Smithsonian Institution Washington, D.C. Publishes Bulletin of the Global Volcanism Network. http://www.volcano.si.edu/gvp/gvn/index.htm Global Volcanism Network Museum of Natural History E-421 Smithsonian Institution Washington, D.C. 20560-0119 phone: 202-357-1511, fax: 202-357-2476, http://www.volcano.si.edu/, e-mail: [email protected] Volcano Disaster Assistance Program This is a cooperative effort between the U.S. Agency for International Development (Office of Foreign Disaster Assistance) and the U.S. Geological Survey. These organizations head a mobile response team that has been mobilized many times since its initiation in 1986, saving numerous lives from areas at risk. Go to http://pubs.usgs.gov/fs/1997/fs064-97/ for more information.


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Chapter 6 Flooding Learning Objectives Water covers about 70 percent of Earth’s surface and is critical to supporting life on the planet. However, water can also be a significant hazard to human life and property in certain situations, such as a flood. Flood is the most universally experienced natural hazard. Floodwaters have killed over 10,000 people in the United States since 1990. For the past decade, property damage from flooding has averaged over $4 billion per year. Flooding is a natural process that will remain a major hazard as long as people live and work in flood-prone areas. Your goals in reading this chapter should be to

• understand the basics of rivers and river processes. • understand the process of flooding and know the difference between upstream

and downstream floods. • know what geographic regions are at risk from flooding. • know the effects of flooding and the linkages with other natural hazards. • recognize the benefits of periodic flooding. • understand how human beings interact with and affect the flood hazard. • be familiar with adjustments we can make to minimize flood deaths and

damage. Chapter Outline 6. Flooding

6.1. An Introduction to Rivers 6.1.1. Earth Material Transported by Rivers 6.1.2. River Velocity, Discharge, Erosion, and Sediment Deposition 6.1.3. Channel Patterns and Floodplain Formation Case Study 6.1: Flooding on the Delta of the Ventura River

6.2. Flooding 6.2.1. Flash Floods and Downstream Floods Case Study 6.2: Magnitude and Frequency of Floods Survivor Story 6.3: Flash Flood

6.3. Geographic Regions at Risk for Flooding 6.4. Effects of Flooding and Linkages between Floods and Other Hazards 6.5. Natural Service Functions

6.5.1. Fertile Lands 6.5.2. Aquatic Ecosystems


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6.5.3. Sediment Supply 6.6. Human Interaction with Flooding

6.6.1. Land-Use Changes 6.6.2. Dam Construction 6.6.3. Urbanization and Flooding Case Study 6.4: The Grand Canyon Flood of 1996 Case Study 6.5: Flash Floods in Eastern Ohio

6.7. Minimizing the Flood Hazard 6.7.1. The Structural Approach

6.7.1.1. Physical Barriers 6.7.1.2. Channelization

6.7.2. Channel Restoration: Alternative to Channelization 6.7.2.1. Kissimmee River Restoration, Florida

6.8. Perception of and Adjustment to the Flood Hazard 6.8.1. Perception of the Flood Hazard Professional Profile 6.6: Professor Nicholas Pinter, Southern Illinois University 6.8.2. Adjustments to the Flood Hazard

6.8.2.1. Flood Insurance 6.8.2.2. Flood-Proofing 6.8.2.3. Floodplain Regulation

6.8.3. Relocating People from Floodplains: Examples from North Carolina and North Dakota

6.8.4. Personal Adjustment: What to Do and What Not to Do Chapter Summary Streams and rivers form a basic transport system of the rock cycle and are a primary erosion agent in shaping the landscape. The region drained by a stream system is called a drainage basin or watershed. Rivers carry chemicals in their dissolved load and sediment in their suspended and bed load. Discharge refers to the volume of water moving past a particular location in a river per unit time.

Sediment deposited by lateral migration of meanders in a stream and by the periodic overflow of the stream banks during a flood forms a floodplain. The configuration of the stream channel as seen in an aerial view is called the channel pattern. A pattern can be braided, meandering, or have both characteristics in the same river.

The natural process of overbank flow is termed flooding. Flash floods in small drainage basins may be produced by intense, brief rainfall over a small area. Downstream floods in major rivers are produced by storms of long duration over a large area that saturate the soil, increasing runoff from thousands of tributary basins.

Flooding magnitude and frequency are difficult to predict on many streams because of changes in land use and limited historical records. The difficulty is especially pronounced for extreme events, such as 100-year floods. The probability that a 100-year


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or greater flood will take place each year is the same, regardless of when the last 100-year flood occurred.

River flooding is the most universally experienced natural hazard. Floods can occur just about anywhere there is water, and much of the United States faces the possibility of flooding. Although flooding causes many deaths and much damage, it does provide natural service functions such as the production of fertile lands, benefits to aquatic ecosystems, and maintenance of ample sediment supplies to naturally subsiding deltas, such as the Mississippi.

Land-use changes, especially urbanization, have increased flooding in small drainage basins by covering much of the ground with impermeable surfaces, such as buildings, parking lots, and roads, thereby increasing the runoff of stormwater. Impermeable surfaces are those through which water cannot penetrate easily.

Loss of life from flooding is relatively low in developed countries where adequate monitoring and warning systems are established, but property damage is much greater than in preindustrial societies because floodplains in industrialized countries are often extensively developed. Most flood deaths in the United States result from people attempting to drive through floodwater.

Environmentally, the best solution to minimizing flood damage is floodplain regulation, but engineering structures will still be needed to protect existing development in highly urbanized areas. These structures include physical barriers, such as levees and floodwalls, and structures that regulate the release of water, such as dams and reservoirs.

Channelization is the straightening, deepening, widening, cleaning, or lining of existing streams, usually with the goal of controlling floods or improving drainage. Channelization has often caused environmental degradation, so new projects must be closely evaluated. In many places, new approaches to channel modification are using natural processes, and in some cases, channelized streams are being restored.

An adequate perception of flood hazards exists at the institutional level; however, on the individual level, more public awareness programs are needed to help people clearly perceive the hazard of living in flood-prone areas.

The best adjustments to the flood hazard include flood insurance, flood-proofing, and floodplain regulation. Floodplain regulation is critical because engineered structures tend to encourage further development of floodplains by producing a false sense of security. The first step in floodplain regulation is flood-hazard mapping, which can be difficult and expensive. Planners use flood-hazard maps to zone flood-prone areas for appropriate use. In some cases, homes in flood-prone areas have been purchased and demolished by the government and people relocated to safe ground. Answers to Review Questions: 1. Explain how levees and floodwalls can actually worsen flooding. (pp. 164–165)

Levees adversely affect the natural processes of the river, and actually make floods worse. The first effect they have is to confine the river to a narrow


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channel, causing the water to rise faster than if it were able to spread across its floodplain. Additionally, since the water can no longer flow across the floodplain it cannot seep into the ground as effectively, and a large amount of water that would normally be absorbed by the soil now must flow through the confined river channel. The floods are therefore larger because of the levees.

2. How is a drainage basin defined? (p. 167)

A drainage basin is the region drained by a single stream or river. It may also be called a watershed, a river basin, or a catchment.

3. What are the three components that make up the total load of a stream? (p. 169) The three components that make up a stream are the bed load, suspended load, and the dissolved load.

4. What were the lessons learned from the 1992 flood of the Ventura River? (p. 169) We learned that a river’s flooding history needs to be studied as part of the flood hazard evaluation; engineering models that predict flood inundation are inaccurate when evaluating distributary channels on river deltas where extensive channel filling, scouring, and lateral movement are likely to occur; historical documents such as maps should be evaluated.

5. Differentiate between braided and meandering channels. (p. 171)

From a bird’s eye view a braided channel weaves across itself. There are islands that divide and reunite the main channel. These rivers are typically composed of sand and gravel. Due to the weaving nature of these channels, they are often wide and shallow. From a bird’s eye view a meandering channel snakes across the surface of the earth. This type of river is by far the most common.

6. Differentiate between pools and riffles. (p. 171)

Pools are deep areas produces by scour (erosion at high flow). Riffles are shallow areas formed by sediment deposition at high flow.

7. How do the characteristics of upstream and downstream floods differ? (p. 176)

Upstream floods occur in upper parts of the drainage basin and in some small drainage basins of tributaries to a larger river. Floods are produced by intense rainfall of short duration over a small area.


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Downstream floods cover wide areas and are produced from storms of long duration, which saturate soil and produce increased runoff from thousands of tributary basins, producing flooding downstream.

8. What are the primary and secondary effects of flooding? (p. 183)

Primary effects of flooding are the effects that are directly caused by the flood. These effects include, but are not limited to injury, loss of life, erosion of stream banks, and damage caused by swift currents, debris, and sediment.

Secondary effects of flooding are indirectly caused by the flood. These effects include short-term pollution of the river, disease, hunger, displacement, and failure of septic systems, wash water ponds, treatment plants, and sanitary sewers.

9. What are the major factors that control damage caused by floods? (p. 183)

Several factors affect the damage caused by floods: land use on the floodplain, depth and velocity of floodwaters, rate of rise and duration of flooding, season in which flooding takes place; quantity and type of sediment deposited by flood waters, and effectiveness of forecasting, warning, and evacuation.

10. What is flashy discharge? How is it hazardous? (p. 188) Flashy discharge is a type of flood characterized by short lag times between rainfall and the very rapid rise and fall of floodwater. These types of floods are characteristic of urbanized areas where ground surfaces have been paved over and the rain waters cannot infiltrate the ground, resulting in hazardous fast moving high floods that rapidly dissipate.

11. How does urbanization affect the flood hazard? (p. 189)

Urbanization increases magnitude and frequency of the flood hazard. The rate of increase is determined by the percent of impervious cover (roads, roofs, etc.), so highly urbanized areas have floods that rise more quickly than in natural areas.

12. What do we mean by floodplain regulation? (p. 199) Floodplain regulation is the best possible adjustment to the flood hazard in urban areas. The objective is to obtain the most beneficial use of floodplains while minimizing flood damage and cost of flood protection. It is a


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compromise between abandonment of floodplains and the indiscriminant use of floodplains.

13. What constitutes channelization? (p. 191) Channelization is the deepening, straightening, widening, cleaning, or lining of existing streams.

14. What is channel restoration? (p. 194) Channel restoration is creating a more natural channel by allowing the stream to meander. One method is to clean urban waste from the channel, allowing the stream to flow freely, while another is to protect existing channel banks by not removing existing trees, while a third is to plant additional native trees and other vegetation.

15. Describe the techniques that are used for flood proofing. (p. 199) Techniques which may be used for flood proofing include raising a foundation above the flood hazard, constructing floodwalls or earthen mounds, using waterproof construction, or installing improved drains with pumps to remove incoming floodwaters.

16. What do we mean when we say that a 10-year flood has occurred? (p. 178) A 10-year flood means that a given level/magnitude of flooding is likely to reoccur once every 10 years. There is a 10% chance per year that a 10-year flood will occur. 1 year/ 10 years= 10%

17. Describe the appropriate safety precautions when walking or driving in a flooded area. What should you do in hilly or mountainous terrain if a flash flood is imminent? (pp. 198–202)

Do not drive under overpasses on highways, or on areas that could be more than knee deep. Remember that knee-deep water is about the cutoff for being able to move cars along with floods. If you are in a mountainous area and a flash flood is coming, get out of your car and run up the nearest hill.


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Answers to Critical Thinking Questions: 1. You are a planner working for a community that is expanding into the headwater

portions of drainage basins. You are aware of effects of urbanization on flooding and want to make recommendations to avoid some of these effects. Outline a plan of action.

Be careful with the percent of land allocated to impervious cover as well as the percent of land served by storm sewers, which can be planned depending on the frequency of floods (a 10-year flood will occur about three times as often if an area is urbanized).

2. You are working for a county flood control agency that has been channelizing

streams for many years. Although bulldozers are usually used to straighten and widen the channel, the agency has been criticized for causing extensive environmental damage. You have been asked to develop new plans for channel restoration to be implemented as a stream maintenance program. Devise a plan of action that would convince the official in charge of the maintenance program that your ideas will improve the urban stream environment and help reduce the potential flood hazard.

In order to reduce the flood hazard, one would have to plant trees native to the area, allow enough room for the stream to meander so that the stream can follow its natural tendency. The trees and added vegetation will help prevent the land from eroding downstream.

3. Does the community you live in have a flood hazard? If not, why not? If there is a

hazard, what has been done or is being done to reduce the hazard? What more can be done?

Most communities in the United States have some flood hazard. Coastal flooding is common, and mountains have the potential for flash flooding. Plains areas often have large river systems prone to large regional floods. Rivers should stop being leveed, and floodplains should be allowed to be floodplains to reduce the flood hazard elsewhere.

Suggested Activities 1. Visit some local farmlands near a stream and search for signs of past stream channels.


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2. Make a tilted sand-filled box or fish tank, with a slope. Watch the erosive power of water drops hitting the sand, then watch how quickly water rivulets can move large quantities of sand downhill. Extrapolate this to a hill-slope scale.

3. Watch videos of flash floods, and discuss the power of water. Discuss how much

force a running stream one foot, two feet, and three feet deep can exert on a car trying to pass through a stream flowing over a roadway. Compare with common items, such as a milk carton filled with water moving toward you with the force exerted by a 15 mph current.

Additional Resources (media, films, articles, journals, web sites) Print Resources Dealing with Flooding Arnold, J.G., Boison, P.J., and Patton, P.C., 1982, Sawmill Brook–An example of rapid

geomorphic change related to urbanization, Journal of Geology, 90, 115–166. Baker, V.R., 1977, Stream-channel responses to floods, with examples from central

Texas, Geological Society of America Bulletin, 88, 1057–1071. Bamford, D., Nov. 18, 2001, Algeria army helps flood victims, BBC News. Belt, C.B., Jr., 1975, The 1973 flood and man’s constriction of the Mississippi River,

Science, 189, 681–684. Berger, E., and Freemantle, T., June 9, 2001, Tropical Storm Alison threatens Texas and

Louisiana coasts, Houston Chronicle. Booth, D.B., 1990, Stream channel incision following drainage basin urbanization, Water

Resources Bulletin, 26, 407–417. CNN, Oct. 20, 2000, Rain eases as Italy, Switzerland battle floods. Collier, M.P., Webb, R.H., and Andrews, E.D., 1997, Experimental flooding in the Grand

Canyon, Scientific American, Jan., 82–89. Coomarasamy, J., Nov. 15, 2001, Floods leave trail of destruction, BBC News. Gordon, N.D., McMahon, T.A., and Finlayson, B.L., 1992, Stream Hydrology—an

Introduction for Ecologists, New York, John Wiley and Sons, 526 pp. Hesse, L.W., and Sheets, W., 1993, The Missouri River hydrosystem, Fisheries, 18, 5–

14. Junk, W.J., Bayley, P.B., and Sparks, R.E., 1989, The flood pulse concept in river–

floodplain systems, Canadian Special Publication Fisheries and Aquatic Sciences, 106, 110–127.

Kusky, T.M., 2007, Floods and Water Supply, Facts on File, Hazardous Earth Set. Leopold, L.B., 1994, A View of the River, Cambridge, Mass., Harvard University Press,

29 pp.


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Leopold, L.B., and Wolman, M.G., 1957, River Channel Patterns–Braided, Meandering, and Straight, U.S. Geological Survey Professional Paper 282-B, 39 pp.

Lewin, J., Bradley, S., and Macklin, G., 1983, Historical valley alluviation in mid-Wales, Geological Journal, 18, 331–350.

Maddock, T., Jr., 1976, A primer on floodplain dynamics, Journal of Soil and Water Conservation, 31, 44–47.

Masterman, S., Oct. 16, 2000, Deadly waters, rains lead to floods, mudslides in Europe, ABC News.

NOAA (National Oceanographic and Atmospheric Administration), 1994, The Great Flood of 1993, Silver Spring, MD.

Noble, C.C., 1980, The Mississippi River flood of 1973, in Coates, D.R. (ed.), Geomorphology and Engineering, London, Allen and Unwin, pp. 79–98.

Parsons, A.J., and Abrahams, A.D., 1992, Overland Flow—Hydraulics and Erosion Mechanics, London, UK, UCL Press Ltd., University College, 391 pp.

Rosgen, D., 1996, Applied River Morphology, Pasoga Springs, Colorado, Wildland Hydrology, 352 pp.

Schumm, S.A., 1977, The Fluvial System, New York, Wiley–Interscience, 338 pp. U.S. Geological Survey, 1979, Storm and Flood of July 31–August 1, 1976, in the Big

Thompson and Cache la Poudre River Basins, Larimer and Weld Counties, Colorado, U.S. Geological Survey Professional Paper, 1115.

Jacobson, R.B., Femmer, S.R., and McKennery, R.A., 2001, Land Use Changes and the Physical Habitat of Streams—A Review with Emphasis on Studies within the U.S. Geological Survey Federal-State Cooperative Program, U.S. Geological Survey Circular 1175, 63 pp.

Nonprint Resources Dealing with Floods Web sites: http://www.nws.noaa.gov/om/brochures/ffbro.htm The National Weather Service, FEMA, and the Red Cross maintain a web site dedicated to describing how to prepare for floods, describing floods of various types, in-depth descriptions of warnings, and types of home emergency kits that families should keep in their homes. http://www.pbs.org/wgbh/nova/flood/ NOVA online has produced an interactive web site that features text and graphics and sounds of floods. It discusses floods from some of the world’s major rivers, including the Yellow, Nile, and Mississippi, and talks about the climate and weather systems that bring fertile soils and fatal floods. A list of resources is available on the site. http://water.usgs.gov/ The United States Geological Survey monitors weather and stream flow conditions nationwide, and also monitors groundwater levels. Its web site also contains information


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on water quality, water use, and contains maps and charts of water use-related issues. The web site has links to other related sites. http://waterwatch.usgs.gov/new/ WaterWatch is a U.S. Geological Survey (USGS) World Wide Web site that displays maps, graphs, and tables describing real-time, recent, and past streamflow conditions for the United States. The real-time information generally is updated on an hourly basis. WaterWatch provides streamgage-based maps that show the location of more than 3,000 long-term (30 years or more) USGS streamgages; use colors to represent streamflow conditions compared to historical streamflow; feature a point-and-click interface allowing users to retrieve graphs of stream stage (water elevation) and flow; and highlight locations where extreme hydrologic events, such as floods and droughts, are occurring. http://www.esri.com/hazards/ FEMA (Federal Emergency Management Agency) and ESRI (Environmental Systems Research Institute) have formed a National Partnership in part aimed at providing multi-hazard maps and information to U.S. residents, business owners, schools, community groups, and local governments via the Internet. The information provided here is intended to assist in building disaster-resistant communities across the country by sharing geographic knowledge about local hazards. http://www.fema.gov/ The Federal Emergency Management Agency responds to major flooding and other disaster events. They maintain the web site above with information on risks, current hazards, and weather information that is crucial in predicting and mitigating floods. Videos: Flood!, 1996, NOVA/WGBH, 60 mins. The Earth Revealed–Rivers, 1992, Annenbergh/CPH, 30 mins. The Earth Revealed–Running Water, Annenberg/CPH, 30 mins. Organizations Dealing with Floods National Weather Service National Operational Hydrologic Remote Sensing Center 1735 Lake Drive W. Chanhassen, MN 55317 952-361-6610 http://www.nohrsc.nws.gov U.S. Army Corps of Engineers US Army Engineer Research and Development Center 3909 Halls Ferry Road ATTN: CEERD-PA-Z


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Vicksburg, MS 39180-6199 ERDC research provides support in: mapping and terrain analysis; infrastructure design, construction, operations, and maintenance; structural engineering; cold regions and ice engineering; coastal and hydraulics engineering; environmental quality; geotechnical engineering; and high performance computing and information technology. http://www.erdc.usace.army.mil/

The Environmental Laboratory monitors floods and other environmental disasters. For more information, go to http://el.erdc.usace.army.mil/index.cfm. American Red Cross P.O. Box 37243 Washington, D.C. 20013 877-272-7337 http://www.redcross.org/ The American Red Cross responds and provides assistance to victims of disasters ranging from apartment fires to floods, earthquakes, hurricanes, and tornadoes.


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Chapter 7 Mass Wasting Learning Objectives Landslides, the movement of materials down a slope, constitute a serious natural hazard in many parts of North America and the world. Landslides are often linked to other hazards such as earthquakes and volcanoes. Most landslides are small and slow, but a few are large and fast. Both may cause significant loss of life and damage to property, particularly in urban areas. Your goals in reading this chapter should be to

• understand slope processes and the different types of landslides. • know the forces that act on slopes and how they affect the stability of a slope. • know the geographic regions that are at risk from landslides. • know the effects of landslides and their linkages with other natural hazards. • understand how people can affect the landslide hazard. • be familiar with adjustments we can make to avoid death and damage caused

by landslides. Chapter Outline 7. Mass Wasting

7.1. An Introduction to Landslides 7.1.1. Slope Processes 7.1.2. Types of Landslides 7.1.3. Forces on Slopes

7.1.3.1. The Role of Earth Material Type A Closer Look 7.1: Forces on Slopes

7.1.3.2. The Role of Slope and Topography 7.1.3.3. The Role of Climate 7.1.3.4. The Role of Vegetation 7.1.3.5. The Role of Water 7.1.3.6. The Role of Time

7.1.4. Snow Avalanches 7.2. Geographic Regions at Risk from Landslides 7.3. Effects of Landslides and Linkages with Other Natural Hazards

7.3.1. Effects of Landslides 7.3.2. Linkages Between Landslides and Other Natural Hazards

7.4. Natural Service Functions of Landslides 7.5. Human Interaction with Landslides

Survivor Story 7.2: Landslide


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Professional Profile: Bob Rasely, Mass Wasting Specialist 7.5.1. Timber Harvesting and Landslides 7.5.2. Urbanization and Landslides Case Study 7.4: Portuguese Bend, California

7.6. Minimizing the Landslide Hazard 7.6.1. Identification of Potential Landslides 7.6.2. Prevention of Landslides

7.6.2.1. Drainage Control 7.6.2.2. Grading 7.6.2.3. Slope Supports

7.6.3. Landslide Warning Systems 7.7. Perception of and Adjustment to the Landslide Hazard

7.7.1. Perception of the Landslide Hazard 7.7.2. Adjustments to the Landslide Hazard

7.7.2.1. Siting of Critical Facilities 7.7.2.2. Landslide Correction

7.7.3. Personal Adjustments: What You Can Do to Minimize Your Landslide Hazard

Chapter Summary The most common landforms are slopes—dynamic, evolving systems in which surficial material is constantly moving downslope, or mass wasting at rates ranging from imperceptible creep to thundering avalanches. Slope failure may involve flowage, sliding, or falling of earth materials; landslides are often complex combinations of sliding and flowage.

The forces that produce landslides are determined by the interactions of several variables: the type of earth material on the slope, topography and slope angle, climate, vegetation, water, and time. Determining the cause of most landslides can be accomplished by examining the relations between forces that tend to make earth materials slide, the driving forces, and forces that tend to oppose movement, the resisting forces. The most common driving force is the weight of the slope materials, and the most common resisting force is the shear strength of the slope materials. Geologists and engineers determine the safety factor of a slope by calculating the ratio of resisting forces to driving forces; a ratio greater than one means that the slope is stable; a ratio less than one indicates potential slope failure. The type of rock or soil on a slope influences both the type and the frequency of landslides.

Water has an especially significant role in producing landslides. Moving water in streams, lakes, or oceans erodes the base of slopes, increasing the driving forces. Excess water within a slope increases both the weight and underground water pressure of the earth material, which in turn decreases the resisting forces on the slope.

Snow avalanches present a serious hazard on snow-covered, steep slopes. Loss of human life from avalanches is increasing as more people venture into mountain areas for winter recreation.


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Landslides may occur just about anywhere that slopes exist. The areas of greatest hazard in the United States include the mountainous areas of the West Coast and Alaska, Rocky Mountains, and Appalachian Mountains. Where landslides do occur, they may cause significant damage and loss of life. They are also linked to other hazards, especially floods, earthquakes, and wildfires.

The effects of land use on the magnitude and frequency of landslides range from insignificant to very significant. Where landslides occur independently of human activity, we need to avoid development or provide protective measures. In other cases, when land use has increased the number and severity of landslides, we need to learn how to minimize their recurrence. In some cases, filling large water reservoirs has altered groundwater conditions along their shores and caused slope failure. Logging operations on weak, unstable slopes have increased landslide erosion. Grading of slopes for development has created or increased landslide problems in many urbanized areas of the world.

To minimize the landslide hazard, it is necessary to establish identification, prevention, and correction procedures. Monitoring and mapping techniques help identify hazardous sites. Identification of potential landslides has been used to establish grading codes, and these codes, in turn, have reduced landslide damage. Prevention of large natural slides is very difficult, but careful engineering practices can minimize the hazard where it cannot be avoided. Engineering techniques for landslide prevention include drainage control, proper grading, and construction of supports such as retaining walls. Efforts to stop or slow existing landslides must attack the processes that started the slides—usually by initiating a drainage program that lowers water pressure in the slope. Even with these improvements in the recognition, prediction, and mitigation of landslides, the incidence of landslides is expected to increase in the twenty-first century.

Most people perceive the landslide hazard as minimal, unless they have prior experience. Furthermore, hillside residents, like floodplain occupants, are not easily swayed by technical information. Nevertheless, the wise person will have a geologist inspect property on a slope before purchasing. Answers to Review Questions: 1. What is a landslide? (p. 210)

A landslide is any type of downslope movement of earth materials including earthflows, debris flows, rock falls, and avalanches.

2. What are slope segments? (p. 210) Slope segments are the different parts of a slope that may be straight or curved, and have different dips and characteristics from adjacent segments.

3. What are the common types of slope segments and how do they differ? (p. 210)


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A free face is a nearly vertical segment. The talus slope forms at the base of the cliff and is composed of fallen rock fragments. An upper convex slope makes up what would be the top of a hill as it begins to slope down. The lower concave slope makes up the valley area and the straight slope is between the two.

4. What are the three main ways that materials on a slope may fail? (p. 211) Materials may fall (freefall), slide, or slump (flow) off the face of a slope.

5. What is the safety factor and how is it defined? (p. 213) The safety factor (SF) is the ratio of the resisting forces to the driving forces.

6. How do slumps (rotational slides) differ from soil slips and rock slides (translational slides)? (p. 214)

Slumps have curved slip surfaces, while translational slides have planar slip surfaces.

7. How does the slope angle affect the incidence of landslides? (p. 215) In general, the steeper the slope the greater the driving force, and therefore as the slope angle increases, the incidence of landslides will increase as well.

8. How and where do debris flows occur? (p. 217) Debris flows are thick mixtures of mud, debris, and water that form on slopes after rainfall. They occur on mountains in North America, more specifically the Great Plains, the Arctic, the Great Lakes, and the southwestern United States.

9. What are the three ways that vegetation is important in slope stability? (p. 219) Vegetation is important because it provides a protective cover that cushions the impact of falling rain, plant roots add strength and cohesion to slope materials, and the vegetation also adds weight to the slope.

10. Why does time play an important role in landslides? (p. 221) Time plays an important role because forces often change with time. What may be affecting a slope one year may have no effect in subsequent years.

11. What is the relationship between the downslope force and normal force? (p. 215)


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The downslope force or driving force (D) is parallel to the slope of the potential slip plane, whereas the normal force (N) is perpendicular.

12. What variables interact to cause snow avalanches? (pp. 221–222)

Snow avalanches are affected by steepness of the slope, stability of the snowpack, and the weather.

13. What is the angle of repose? (p. 222) The angle of repose is the steepest angle at which any snow or loose material is stable.

14. What are the two types of snow avalanches and how do they differ? (p. 222) The two types of snow avalanche include loose snow avalanches—which start at a point and widen as they move downhill—and slab avalanches, which start as cohesive blocks of snow and ice that move downslope.

15. How might processes involved in urbanization increase or decrease the stability of slopes? (pp. 227–231)

Urbanization, the expansion of urban areas, transportation networks, and natural resource use, has increased the number and frequency of landslides. Many slopes are oversteepened to make way for roads, buildings, and other features. Natural vegetation is sometimes removed, further reducing slope stability. However, where these problems are recognized, the number of events has decreased due to preventative methods.

16. What types of surface features are associated with landslides? (p. 231)

Surface features associated with landslides are crescent-shaped cracks on a hillside, a tongue-shaped area of bare soil on a hillside, large boulders at the base of a cliff, exposed bedrock laying parallel to the cliff, tongue-shaped masses of sediment, and irregular land surface at the base of the slope.

17. What are the main steps that can be taken to prevent landslides? (p. 232) Some of the main steps taken to avoid landslides are drainage control, grading, and slope supports.



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1. Your consulting company is hired by the national park department in your region to

estimate the future risk from landsliding. Develop a plan of attack that outlines what must be done to achieve this objective.

We will determine the safety factor (SF; the ratio of the resisting forces to the driving forces) for different slopes in the area, and determine how this might change with seasons (wet, ice, dry, etc.), and also factor in such variables as likelihood of earthquakes shaking and loosening slope material. We will look for records of past landslides and slope failure, and try to estimate how frequently such events occur. We will make recommendations on how to use drainage control, to grade the hills and use slope supports where needed. We will also make recommendations on how to inform the public of the hazard and teach them about prevention.

2. Why do you think that few people are easily swayed by technical information concerning hazards such as landslides? Assume you have been hired by a municipality to make its citizens more aware of landslide hazards on the steep slopes in the community. Outline a plan of action and defend it.

Few people are swayed because few people actually see landslides as a plausible threat. It always appears to be something that happens to someone else. However, if citizens see maps that include the risk factors for their homes, and are educated (through pictures and examples) of what landslides can do, they are more likely to listen. They should know to listen to authorities when they are warned that there may be an increased likelihood of slope failure, such as after heavy rainy seasons.

3. The Wasatch Front in central Utah frequently experiences wildfires followed by debris flows that exit mountain canyons and flood parts of communities built next to the mountain front. You have been hired by the state emergency management office to establish a warning system for subdivisions, businesses, and highways in this area. How would you design a warning system that will alert citizens to evacuate hazardous areas?

First the region would need to be mapped for hazard potential, and dangerous low-lying areas or alluvial fans identified. Maps and escape routes should be posted on signs in these areas. The warning system would notify people via siren, TV, and radio, informing people of dangerous areas and sending evacuation notices if needed.



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1. Put a soda can on an inclined slope like a board, and measure the angle at which it

first begins to slide as the dip angle of the board is increased. Do the same experiment with the board and base of the soda can wet. Next, open the soda (or beer) can, drink the contents, and chill the can in a freezer until quite cold. Then repeat the experiment. Note how the cold air is trapped inside the can, and as the air in the can heats up, it expands, increasing the pressure (fluid pressure) and effectively reducing the friction, allowing the can to slide at low angles. Discuss the importance of water as a lubricating agent that aids downslope flow.

2. Take a field trip to a mountain front and identify the various slope elements, and

discuss how far the various boulders and blocks in the talus slope have traveled. Discuss how long it may have taken for the talus to have accumulated.

Additional Resources (media, films, articles. journals, web sites) Print Resources Dealing with Mass Wasting Armstrong, B.R., and Williams, K., 1992, The Avalanche Book, Armstrong, Colo.,

Fulcrum Publishing. Brabb, E.E., and Harrod, B.L., 1989, Landslides: Extent and Economic Significance,

Proceedings of the 28th International Geological Congress: Symposium on Landslides, Washington, D.C., July 17, Rotterdam, A.A. Balkema.

Coates, D.R., (ed.), 1977, Landslides, Geological Society of America Reviews in Engineering Geology, 3, 278.

Hsu, K.J., 1989, Catastrophic debris streams (sturzstroms) generated by rockfalls, Geological Society of America Bulletin, 86, 129–140.

Kiersch, G.A., 1964, Vaiont reservoir disaster, Civil Engineering, 32–39. Kusky, T.M., 2007, Landslides, Facts on File, Hazardous Earth Set. Matthews, W.H., and McTaggert, K.C., 1978, Hope rockslides, British Columbia, in B.

Voight, (ed.)., Rockslides and Avalanches, Amsterdam, Elsevier 1, pp. 259–275. Nilsen, T.H., and Brabb, E.E., 1975, Landslides, in R.D. Borcherdt (ed.), Studies for

Seismic Zonation of the San Francisco Bay Region, U.S. Geological Survey Professional Paper 941A.

Norris, R.M., 1990, Sea cliff erosion, Geotimes 35, 16–17. Pinter, N., and Brandon, M., 2000, How erosion builds mountains, in Scientific

American, Earth from the Inside Out, edited by J. Rennie, pp. 24–29. Plafker, G., and Ericksen, G.E., 1978, Nevados Huascaran avalanches, Peru, Chapter 8 in

B. Voight (ed.), Rockslides and Avalanches, Amsterdam, Elsevier.


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Schultz, A.P., and Southworth, C.S., (eds.), 1987, Landslides in Eastern North America, U.S. Geological Survey Circular 1008, 43 pp.

Schuster, R.L., and Fleming, R.W., 1986, Economic losses and fatalities due to landslides, Bulletin of the Association of Engineering Geologists, 23, 11–28.

Shaefer, S.J., and Williams, S.N., 1991, Landslide Hazards, Geotimes, 36, 20–22. Varnes, D.J., 1978, Slope movement types and processes, in R.L. Schuster and R.J.

Krizek (eds.), Landslides, Analysis and Control, (Chapter 2), Washington, D.C., National Academy of Sciences.

Nonprint Resources Dealing with Mass Wasting Web sites: http://www.usgs.gov/themes/hazard.html. U.S. Geological Survey web site, with pages on landslide hazards (Fact Sheet FS-0071-00) and downslope flow hazards. http://pubs.usgs.gov/fs/fs-0071-00/fs-0071-00.pdf http://www2.fiu.edu/~longoria/natural/mass/mmain.htm Florida International University. Site contains illustrations and information on mass wasting. Contains links to other helpful sites. http://earthsci.org/ Earth Science Australia - for people with an interest in earth science http://earthsci.org/flooding/unit3/u3-02-03.html Contains some good information on mass wasting associated with floods. Videos: Debris Flow Dynamics, 1984, U.S. Geological Survey, 23 mins. Landslide: Gravity Kills, 1999, Discovery Channel, 52 mins. Raging Planet: Avalanche, 1997, Discovery Channel, 50 mins. Organizations Dealing with Downslope Flows Federal Emergency Management Agency (FEMA) 500 C Street, SW Washington, D.C. 20472 202-646-4600 http://www.fema.gov U.S. Geological Survey Federal Center Box 25046, MS 967


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Denver CO, 80225-0046 303-273-8500 http://www.usgs.gov/ U.S. Army Corps of Engineers Headquarters 441 G. Street, NW Washington, D.C. 20314 phone: 202-761-0008, fax: 202-761-1683 http://www.usace.army.mil/


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Chapter 8 Subsidence and Soils Learning Objectives Subsidence, the sinking of the land, and expansion and contraction of the soil are important geologic processes capable of causing extensive damage in some areas of the world. Your goals in reading this chapter should be to

• know what a soil is and the processes that form and maintain soils. • understand the causes and effects of subsidence and volume changes in the soil. • know the geographic regions at risk for subsidence and volume changes in the

soil. • understand the hazards associated with karst regions. • recognize linkages between subsidence, soil expansion and contraction, and other

hazards, as well as natural service function of karst. • understand how humans interact with the subsidence and soil hazards. • know what can be done to minimize the hazard from subsidence and volume

changes in the soil. Chapter Outline 8. Subsidence and Soils

8.1. Soil and Hazards 8.1.1. Soil Horizons 8.1.2. Soil Color 8.1.3. Soil Texture 8.1.4. Relative Soil Profile Development 8.1.5. Water in Soils 8.1.6. Soil Classification

8.1.6.1. Soil Taxonomy 8.1.6.2. Engineering Classification of Soils

8.2. Introduction to Subsidence and Soil Volume Change 8.2.1. Karst

8.2.1.1. Sinkholes 8.2.1.2. Cave Systems 8.2.1.3. Tower Karst Survivor Story 8.1: Sinkhole Drains Lake 8.2.1.4. Disappearing Streams


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8.2.1.5. Springs 8.2.2. Thermokarst 8.2.3. Sediment and Soil Compaction

8.2.3.1. Fine Sediment 8.2.3.2. Collapsible Soils 8.2.3.3. Organic Soils

8.2.4. Earthquakes 8.2.5. Underground Drainage of Magma 8.2.6. Expansive Soils Case Study 8.2: Subsidence of the Mississippi Delta 8.2.7. Frost-Susceptible Soils

8.3. Regions at Risk for Subsidence and Soil Volume Change 8.4. Effects of Subsidence and Soil Volume Change

8.4.1. Sinkhole Formation 8.4.2. Groundwater Conditions 8.4.3. Damage Caused by Melting Permafrost 8.4.4. Coastal Flooding and Loss of Wetlands 8.4.5. Damage Caused by Soil Volume Change

8.5. Linkages Between Subsidence, Soil Volume Change, and Other Natural Hazards 8.6. Natural Service Functions of Subsidence and Soil Volume Change

8.6.1. Water Supply 8.6.2. Aesthetic and Scientific Resources 8.6.3. Unique Ecosystems

8.7. Human Interaction with Subsidence and Soil Volume Change 8.7.1. Withdrawal of Fluids 8.7.2. Underground Mining 8.7.3. Melting Permafrost 8.7.4. Restricting Deltaic Sedimentation 8.7.5. Altering Surface Drainage Professional Profile 8.3: Helen Delano, Environmental Geologist 8.7.6. Poor Landscaping Practices

8.8. Minimizing Subsidence and Soil Volume Change 8.8.1.1. Artificial Fluid Withdrawal 8.8.1.2. Regulation Mining 8.8.1.3. Prevention of Damage from Thawing Permafrost 8.8.1.4. Reducing Damage from Deltaic Subsidence 8.8.1.5. Managing Drainage of Organic and Collapsible Soils 8.8.1.6. Prevention of Damage from Expansive Soils

8.9. Perception of and Adjustment to Subsidence and Soil Volume Change 8.9.1. Perception of Subsidence and Soil Volume Change 8.9.2. Adjustment to Subsidence and Soil Volume Change

8.9.2.1. Geologic and Soil Mapping 8.9.2.2. Surface Features 8.9.2.3. Subsurface Surveys


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Chapter Summary

Engineers define soil as earth material that may be removed without blasting, whereas, to a soil scientist, soil is solid earth material that can support rooted plant life. A basic understanding of soils and their properties is becoming crucial in several areas of environmental geology, including land-use planning, waste disposal, and evaluation of natural hazards such as flooding, landslides, and earthquakes.

Soils result from interactions of the rock and hydrologic cycles. As open systems, they are affected by variables such as climate, topography, parent material, time, and organic activity.

Soil-forming processes tend to produce distinctive soil layers, or horizons, defined by the processes that formed them and the type of materials present. Of particular importance are the processes of leaching, oxidation, and accumulation of materials in various soil horizons. Development of the argillic B horizon, for example, depends on the translocation of clay minerals from upper to lower horizons. Three important properties of soils are color, texture (particle size), and structure (aggregation of particles).

An important concept in studying soils is relative profile development. Young soils are weakly developed. Soils older than 10,000 years tend to show moderate development, characterized by stronger development of soil structure, redder soil color, and more translocated clay in the B horizon. Strongly developed soils are similar to those of moderate development, but the properties of the B soil horizon tend to be better developed. Such soils can range in age from several tens of thousands of years to several hundred thousand years or older. A soil chronosequence is a series of soils arranged from youngest to oldest in terms of relative soil profile development. Establishment of a soil chronosequence in a region is useful in evaluating rates of processes and recurrence of hazardous events such as earthquakes and landslides.

A soil may be considered as a complex ecosystem in which many types of living things convert soil nutrients into forms that plants can use. Soil fertility refers to the capacity of the soil to supply nutrients needed for plant growth. Soil has a solid phase consisting of mineral and organic matter; a gas phase, mostly air; and a liquid phase, mostly water. Water may flow vertically or laterally through the pores (spaces between grains) of a soil. The flow is either saturated (all pore space filled with water) or, more commonly, unsaturated (pore space partially filled with water). The study of soil moisture and how water moves through soils is becoming an important topic in environmental geology.

Several types of soil classification exist, but none of them integrate both engineering properties and soil processes. Environmental geologists must be aware of both the soil science classification (soil taxonomy) and the engineering classification (unified soil classification).

Subsidence is a type of ground failure characterized by nearly vertical deformation, or the downward sinking, of earth materials. This failure may be caused by natural processes, human activities, or a combination of the two. Most subsidence is caused by the underground dissolution of soluble rocks such as limestone, dolostone,


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marble, rock salt, and rock gypsum. Other causes of subsidence are the lowering of groundwater levels and fluid pressures in sediment, the thawing of permafrost, reduced sedimentation on delta plains, the flooding of collapsible soils, and the drainage of organic soils. Earthquakes, the deflation of magma chambers, and the drainage of lava tubes also may cause some subsidence.

Underground dissolution of limestone by acidic groundwater creates a landscape of caves and sinkholes known as karst topography. Other karst features include disappearing streams, springs, and tower karst. Most sinkholes form by the slow dissolution of limestone. Other sinkholes form from the collapse of cave roofs. This collapse is often caused by a falling groundwater table during a drought, or by an increase in pumping of water wells. Karst topography also develops where layers of highly soluble rock salt or rock gypsum are near the surface.

During the past several decades, the thawing of permafrost has become a major hazard in Arctic and near-Arctic regions. Most of this melting is a direct result of climatic warming. Thawing permafrost causes subsidence and structural damage, as well as the formation of thermokarst, a terrain consisting of uneven ground with sinkholes, mounds, ponds, and caves.

Loosely compacted fine sediment subsides where the groundwater table has fallen or fluid pressure has been reduced. Groundwater changes may be natural or result from human activities, such as groundwater mining. This subsidence is often irreversible because of the drying of underground layers of very fine sediment. Surface features associated with this compaction include large earth fissures or desiccation cracks.

Marine deltas are areas of natural compaction and subsidence. In these areas, the continual deposition of sediment on the delta plain generally keeps up with the compaction of sediment underground. Reducing or stopping sedimentation on the delta plain by the construction of dams, levees, and canals causes the delta surface to subside below the sea. This subsidence destroys wetlands and can produce flooding in urban areas such as New Orleans.

Soil expansion and contraction can cause the land surface to either heave upward or sink downward. Both heaving and sinking occur in expansive and frost-susceptible soils, and sinking takes place in collapsible soils.

Expansive soils are those that swell when they become wet and shrink when they dry, commonly a result of changes in the amount of water clinging onto the surface of fine smectite clay. Wetting and drying of this clay cause the expansion and contraction of the soil. These volume changes can cause extensive structural damage. Factors that affect the moisture content of an expansive soil include climate, vegetation, topography, and drainage.

Frost-susceptible soils are those that are likely to accumulate ice in pockets or lenses between silty earth material. Growth of these ice accumulations displaces the surrounding soil and produces frost heaving. The upward heaving and later thawing of the soil cause structural and pavement damage in areas underlain by permafrost and in soils that are only intermittently frozen.

Collapsible soils are normally dry with particles loosely packed or weakly cemented together. These soils are susceptible to subsidence when water ponds on the surface.


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Subsidence is a hazard in more than 45 states in the United States and most Canadian provinces. In areas of karst topography, hazards include sinkhole collapse, groundwater pollution, and unreliable water supplies. Large areas of karst topography are found in (1) a region extending through the states of Tennessee, Virginia, Maryland, and Pennsylvania; (2) south-central Indiana and west-central Kentucky; (3) the Salem-Springfield plateaus of Missouri and Arkansas; (4) central Texas; (5) central Florida; and (6) Puerto Rico.

Soil volume change is also a common hazard in many areas. Permafrost and frost-susceptible and organic soils are common in Alaska, Canada, and Russia. Organic soils are also abundant in the Upper Midwest, the Pacific Northwest, and the Gulf and Atlantic Coasts in the United States. Frost-susceptible soils also occur in areas of the northern contiguous United States and at high altitudes in mountainous areas. Collapsible soils occur in arid and semiarid regions, such as the southwestern United States. Expansive soils are a problem primarily in the western United States and Canada. These soils are responsible for significant economic damage each year, mostly from damage to highways, buildings, pipelines, and other structures.

Although subsidence causes numerous problems, it has benefits in the development of karst topography. About 25 percent of the world’s population gets its drinking water from karst formations. Karst regions offer important aesthetic and scientific resources. They are home to rare creatures that are specially adapted to live underground.

Human beings exacerbate subsidence by removal of subsurface fluids, underground mining, melting permafrost, reduction of sediment accumulation on deltas, and the draining of organic soils. The effects of soil volume change can be intensified by using poor landscaping and drainage practices on expansive and collapsible soils. Natural subsidence and changes in the volume of the soil are difficult to prevent, but human-induced subsidence may be avoided or minimized. Methods for limiting human-induced subsidence include injecting water during crude-oil production and regulating groundwater pumping and underground mining. Problems with soil volume change may be minimized with sound construction and landscaping techniques. An understanding of the local geologic and hydrologic systems can help prevent water pollution in karst areas.

Adjustments to the subsidence and soil volume change hazard include identification of problem areas through geologic, soil, and subsurface mapping. Homeowners can protect themselves with insurance that covers the subsidence and soil volume change hazards in their area.

Answers to Review Questions: 1. What is soil, and soil profile? (p. 244)

To soil scientists, soil is solid earth material that has been altered by physical, chemical, and organic processes such that it can support rooted plant life. To engineers, on the other hand, soil is any solid earth material that can be


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removed without blasting. Soil profile is vertical and horizontal movements of the materials in a soil system creating a distinct layering, parallel to the surface.

2. How does limestone bedrock dissolve? (p. 251) Limestone will dissolve if the percolating water—fresh surface water that flows through holes in the rock—is acidic.

3. Which rock types are especially susceptible to dissolution? (pp. 250–251)

Several common sedimentary rocks—rock salt and rock gypsum, limestone and dolostone, and marble—are easily dissolved.

4. What features are found in karst areas? (pp. 250–255)

Sinkholes, rolling hills (caused by an area of subsidence), cave systems, disappearing streams, collapse sinkholes, tower karst, and springs are all found in karst areas.

5. Describe the two processes by which sinkholes form. (p. 253) Solutional sinkholes form by dissolution on the top of a buried bedrock surface. This occurs where the downward infiltration of acidic groundwater becomes concentrated in holes created by joints and fractures. In the formation of these sinkholes, groundwater is typically drawn into a cone above a hole in the limestone, like water being drawn into a sink drain. Collapsible sinkholes develop by the collapse of surface or near-surface material into an underground cavern.

6. How do cave systems form? (p. 253) Cave systems form when solutional pits enlarge and move downward. The primary system for cave forming is groundwater moving through rock, typically following joint systems.

7. Describe the natural cycle of permafrost thawing and how climate change has

influenced this cycle. (p. 255) Permafrost occurs in polar regions and at high altitude where much of the soil and underlying rock remain frozen year round. As the ice in permafrost soil melts, there can be great subsidence of several meters or more. Without human impact, permafrost thawing will melt the few meters of soil and will refreeze in


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the winter; however, irregularly large amounts of permafrost have thawed due to global warming. This irregularity is referred to as thermokarst terrain.

8. What keeps a delta plain from subsiding? (p. 255) In a delta plain, natural subsidence must be balanced by additional sediment to keep the land surface of the delta from sinking below sea level. Without the addition of sediment a delta plain tends to subside.

9. What happens to organic soils when they are drained of water? (p. 256) When organic soils are drained of water, they dry out and compact. After they are exposed for a period of time to weathering processes, they literally disappear.

10. Explain how expansive soils shrink and swell, how frost heaving occurs, and how collapsible soils subside. (pp. 256–262)

Expansive soils swell due to the absorption of water during wet seasons, and they shrink as water evaporates during dry seasons. Frost heaving occurs because of the 9 percent volume increase that occurs when water changes to ice. Collapsible soils subside due to percolating water weakening the bonds of clay particles and dissolving minerals that hold the soil together.

11. What natural and artificial features might indicate the presence of expansive soils? (p. 260)

Deep cracks, popcorn like weathering texture, an alternating pattern of mounds and depressions, a series of waves and bumps in asphalt soils, tilting and cracking of concrete in sidewalks and foundations, and random tilting of gravestones and utility poles are all signs of expansive soils.

12. What factors influence the moisture content of expansive soils? (p. 260)

Climate, vegetation, topography, drainage, and quality of construction are all factors that affect the moisture content of a soil.

13. Explain how subsidence might be connected to earthquakes in subduction zones. (p.

257)

Subsidence may be connected to earthquakes in subduction zones because the strain between great earthquakes which builds up due to “locked” plates may cause the continental plate to buckle. This drags the underwater seaward edge of the continent downward and produces an upward bulge along the coast.


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14. How can subsidence occur on a volcano? (p. 257) When the magma is forced out of the volcano, the magma chamber contains less material because the lava is now on the surface. The drained magma chamber buckles under the weight of the volcano, causing subsidence.

15. Identify the types of subsidence hazards that are likely to be found in the: (p. 275) a. Eastern United States: Karst subsidence and groundwater withdrawal

subsidence b. Western United States: Karst, subsidence caused by compaction of sediment,

expansive soils, groundwater withdrawal subsidence, and seismic related subsidence

c. Alaska and Canada: Permafrost, expansive soils, and seismic related subsidence

16. Which subsidence or soil volume change hazards cause the most economic damage?

Why are these hazards so costly? (p. 264) Karst and expansive soils cause the most damage each year. Karst damage is expensive because it causes sinkholes, groundwater pollution, and variable water supplies. Expansive soils are expensive because they cause damage to highways, buildings, bridges, pipelines, and other structures.

17. What factors contribute to the formation of sinkholes? (p. 264)

Some factors which contribute to the formation of sinkholes are the lowering of groundwater, dissolution of limestone, and human activities that cover any evidence of a possible sinkhole, causing huge amounts of damage after building construction after the evidence was buried.

18. Why is groundwater sometimes polluted in karst terrains? (p. 265) Sometimes pollution comes from sinkholes which have been used for waste disposal, or when polluted surface water flows into groundwater through caves and fractures in the rock.

19. What are the natural and anthropogenic causes for subsidence of the Mississippi Delta and New Orleans? (pp. 265–266)

New Orleans is below sea level. The only thing preventing it from disaster is the ring of levees surrounding the city. If a hurricane comes. many people will be trapped as there is only one exit out of the city, and a large tidal surge could inundate much of the city. Further, if the Mississippi changes course, then the current Mississippi delta will subside below sea level.


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20. What types of damage are caused by the thawing of permafrost, shrinking and

swelling of soil, and frost heaving? (p. 267)

The damage caused from the thawing of permafrost includes damage to highways, buildings, and other structures. Shrinking and swelling of soil causes similar damage; as the volume of the ground and soil changes, overlying buildings, roads, and buried pipelines must also change shape or fracture to accommodate the changing soil volume. Most structures crack.

21. How are subsidence and soil volume change hazards linked to changes in climate? (p. 267)

Drought conditions lower the groundwater table, resulting in shrinkage of unconsolidated earth materials. As global warming melts the permafrost in the Arctic, it contributes to the increasing sea level.

22. What are the natural service functions of subsidence? (p. 268) Karst terrains are some of the world’s most precious sources of drinkable water. Forty percent of the U.S. population relies on karst terrains for drinking water.

23. Explain how fluid withdrawal and mining can increase subsidence. (pp. 269–270) Both fluid withdrawal and mining increase subsidence because the techniques remove material from the ground. The surface above the void exerts force downward. Eventually there is a point where the surface can no longer be supported at its original height and so it subsides.

24. How can we minimize or adjust to subsidence and soil volume change hazards? (p. 274)

Injection wells can minimize or stop subsidence from fluid withdrawal. Preventing mining in urban areas will prevent the damage caused by subsidence. Buildings on permafrost are now installing screw jacks or lattice-like foundations to allow for the freezing and thawing. For communities on deltas, the only option is to continue to raise the levees and allow swamps in nearby unpopulated areas. In general, people should avoid building on subsidence-prone areas.



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1. You are considering building a home in rural Kentucky. You know the area is underlain by limestone, and are concerned about possible karst hazards. What are some of your concerns? What might you do (or have done) to determine where to build your home?

The main concern is whether or not the ground the building is placed on is strong enough to support the weight of the structure. Some of the concerns are that when building begins, the weight of the house may weaken the ground enough so that it collapses. Another concern is that karst features may form in the near future. Testing the ground stability and determining that it is strong enough to support a large weight is key. Ground-penetrating radar and drilling can help determine if there is a cave system at shallow depths that needs to be considered before building. Runoff and neighboring houses are a good place to start to determine if there have been damages to houses in the area in the past.

2. You work in the planning department in one of the parishes (counties) close to New Orleans. What would you advocate in the long term and in the short term to protect your community from subsidence and flooding? Consider both regional and local solutions to the problem.

I would consider allowing the river to run the most natural course as it possibly can and to invest in further research regarding long-term problems which may have real-time effects on the city. Building up levees may temporarily keep floods out, but they also keep the replenishing muds from building up the surface layer to keep pace with subsidence, and it will cause aggradation (raising) of the base of the stream channel. Levees should not be built unless their consequences are understood on a local and regional scale.

3. You have inherited a ranch house built on a concrete slab on clay soil in a suburb east of Denver, Colorado. What would you look for, or do, to determine if the house is on expansive soil? If you found that soil was expansive, how would you minimize damage from the sinking and swelling of soil?

I would look for deep cracks, popcorn-like weathering texture, an alternating pattern of mounds and depressions, a series of waves and bumps in asphalt soils, tilting and cracking of concrete in sidewalks and foundations, and random tilting of gravestones and utility poles to determine if the soil is expansive. To minimize damage, drainage should be directed away from the house, and trees and shrubs that take up moisture should not be planted too close to the house.

4. You, or your parents, would like to build a retirement home in a desert development in Arizona or New Mexico. What would you look for to determine if subsidence or soil volume change is a potential problem? What could you do to protect your investment?


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Look for any one of the following: karst topography or karst plains nearby, also look for sink holes, disappearing streams, springs, get a map of the underground caverns in the area. Get a copy of the water table records in the area. Avoid building in these areas. To protect your investment, it may be wise to spend a little to have a geological study and soil analysis done to find a location where the bedrock is solid to a suitable depth to withstand the weight of the future retirement home, and be sure there are no fractures for acidified water to seep in and dissolve the calcium carbonate-rich bedrock beneath the future retirement home.

5. As a town council representative in a small village in New England or Ontario,

Canada, you have been asked to approve a building permit on property that is partly underlain by silty glacial deposits and partly by a marsh. What questions should you ask the permit applicant regarding his or her planned construction on the silty soil, and his or her proposal to drain and build on the wetland?

Are these soils collapsible or organic in origin? If so, what are the plans for mitigation to prevent the future collapse, subsidence and or decomposition once the water is drained?

Suggested Activities 1. In the sandbox used previously, make a slope of sand and add water to the deep end.

With a straw, withdraw water from near the coast, and measure how much subsidence is observed.

2. Visit a local karst terrain, pointing out sinkholes, caves, collapsed valleys, etc. Additional Resources (media, films, articles, journals, web sites) Print Resources Dealing with Subsidence Hazards Beck, B.F., 1989, Engineering and Environmental Implications of Sinkholes and

Karst, Rotterdam: Balkema.


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Dolan, R., and Grant Goodell, H., 1986m Sinking cities, American Scientist, v. 74, no. 1, 38–47.

Drew, D., 1985, Karst Processes and Landforms, MacMillan Education Press, 63 pp.

Ford, D., and Williams, P., 1989, Karst Geomorphology and Hydrology, London, Unwin-Hyman, 601 pp.

Holzer, T.L., ed., 1984, Man-induced land subsidence, Geological Society of America, Reviews in Engineering Geology, VI.

Jennings, J.N., 1985, Karst Geomorphology, Oxford: Basil Blackwell. Kusky, T.M., 2007, Landslides; Soil and Mineral Hazards, Facts on File, Hazardous

Earth Set. White, W.B., 1988, Geomorphology and Hydrology of Karst Terrains, Oxford,

Oxford University Press, 464 pp. Nonprint Resources Dealing with Subsidence Hazards http://www.lgt.lt/geoin/doc.php?did=cl_karst Web site of the U.S. Global Change Research Office describes karst activity, its significance, and causes, as well as types of monitoring and hazards. http://www.karstwaters.org/ Web site of the Karst Waters Institute. Offers excellent descriptions of karst phenomenon, hazards, waters, and researchers in the field. Also contains a lexicon (glossary) of karst terminology. http://www.sgp.org.pl/spec/linkk.html Karst Link Page. Links to sites about caves and karst systems, arranged by continent and region. The massive index is maintained by The Association of Polish Geomorphologists. http://www.nature.nps.gov/nckri/map/links/states.htm National Karst Map Link Page http://www.nature.nps.gov/nckri/map/maps/index.html National Karst Maps National Cave and Karst Research Institute http://www.nature.nps.gov/nckri/index.htm Organizations Dealing with Subsidence Disasters United States Environmental Protection Agency Office of Research and Development


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Washington, D.C. 20460 www.epa.gov/ Works with other government and private organizations to monitor subsidence and sinkhole hazards. The Karst Waters Institute PO Box 537 Charles Town, WV 25414 304-725-1211 www.karstwaters.org/ The Karst Waters Institute (KWI) is a 501 (c)(3) non-profit institution whose mission is to improve the fundamental understanding of karst water systems through sound scientific research and the education of professionals and the public. The institute is governed by a board of directors and does not have or issue memberships. Institute activities include the initiation, coordination, and conduct of research, the sponsorship of conferences and workshops, and occasional publication of scientific works. KWI supports these activities by acting as a coordinating agency for funding and personnel, but does not supply direct funding or grants to individual researchers. As one way of increasing public awareness of karst and cave protection, the Institute publishes a list of the Top 10 endangered karst environments in the world. The third annual list is now available. Solution Mining Research Institute 3336 Lone Hill Lane Encinitas, California 92024-7262 phone: 858-759-7532, fax: 858-759-7542 e-mail: [email protected] web site: www.solutionmining.org The Solution Mining Research Institute (SMRI) is a private organization interested in the production of salt brine and the utilization of the resulting caverns for the storage of oil, gas, chemicals, compressed air and waste, and other mining activities. SMRI is a worldwide organization with more than seventy members in Asia, Europe and North and South America. Participation by operators, researchers, suppliers, consultants, educators and government regulators is encouraged. Activities include: Sponsoring and funding research, holding technical meetings, conducting classes, maintaining a library, and participating in the development of government regulations.


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Chapter 9 Atmosphere and Severe Weather Learning Objectives Atmospheric processes and energy exchanges are driven by Earth’s energy balance and linked to climate and weather. Hurricanes, thunderstorms, tornadoes, blizzards, ice storms, dust storms, and heatwaves, as well as flash flooding resulting from intense precipitation, are all natural processes that are hazardous to people. These severe hazards affect considerable portions of North America and are responsible for causing significant death and destruction each year. Your goals in reading this chapter should be to:

• understand Earth’s energy balance and energy exchanges that produce climate

and weather. • know the different types of severe weather events. • know the main effects of severe weather events, as well as their linkages to

other natural hazards. • recognize some natural service functions of severe weather. • understand how human beings interact with severe weather hazards and how

we can minimize the effects of these hazards.

Chapter Outline 9. Atmosphere and Severe Weather

9.1. Energy 9.1.1. Types of Energy 9.1.2. Heat Transfer

9.2. Earth’s Energy Balance 9.2.1. Electromagnetic Energy 9.2.2. Energy Behavior

9.3. The Atmosphere 9.3.1. Composition of the Atmosphere 9.3.2. Structure of the Atmosphere

9.4. Weather Processes 9.4.1. Atmospheric Pressure and Circulation 9.4.2. Unstable Air 9.4.3. Fronts

A Closer Look 9.1: Coriolis Effect 9.5. Hazardous Weather

9.5.1. Thunderstorms 9.5.1.1. Severe Thunderstorms


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Case Study 9.2: Lightning Survivor Story 9.3: Struck by Lightning

9.5.1.2. Hail 9.5.2. Tornadoes

9.5.2.1. Classification of Tornadoes 9.5.2.2. Occurrence of Tornadoes

9.5.3. Blizzards and Ice Storms 9.5.3.1. Blizzards 9.5.3.2. Ice Storms

Professional Profile 9.4: Sarah Tessendorf – Severe Storm Meteorologist 9.5.4. Fog 9.5.5. Drought 9.5.6. Mountain Windstorms 9.5.7. Dust and Sand Storms

Case Study 9.5: The Great Northeastern Ice Storm of 1998 9.5.8. Heatwaves

9.6. Human Interaction with Weather 9.7. Linkages with Other Hazards 9.8. Natural Service Functions of Severe Weather 9.9. Minimizing Severe Weather Hazards

9.9.1. Forecasting and Predicting Weather Hazards 9.9.1.1. Watches and Warnings

Case Study 9.6: Europe’s Hottest Summer in More Than 500 Years 9.9.2. Adjustment to Severe Weather Hazards

9.9.2.1. Mitigation 9.9.2.2. Preparedness and Personal Adjustments

Chapter Summary

Earth receives energy from the Sun, and this energy affects the atmosphere, oceans, land, and all living things before being radiated back into space. Although Earth intercepts only a tiny fraction of the total energy emitted by the Sun, this energy sustains life on Earth while it drives many processes at or near Earth’s surface, such as the circulation of air masses on a global scale. Potential, kinetic, and heat energy are three primary forms of energy. In the atmosphere, heat energy occurs as sensible heat that can be measured or latent heat that is stored. Latent heat is either absorbed or released in phase changes. Evaporation absorbs heat and cools the air, whereas condensation, which forms clouds, releases latent heat and warms the air. Energy transfer occurs by convection, conduction, and radiation. Of these, convection is the most significant in producing clouds and severe weather. The Earth receives primarily short-wavelength, electromagnetic energy from the Sun. This energy is either reflected, scattered, transmitted, or absorbed on Earth. Dark-colored surfaces reflect less and absorb more solar energy and thus generally heat up.


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Most absorbed solar energy is radiated back into the atmosphere as long-wavelength, infrared radiation.

Most weather occurs in the troposphere, the lowest of the five major layers of the atmosphere. Clouds in the troposphere are made of water droplets and ice crystals. Changes in atmospheric pressure and temperature are responsible for air movement. Air flows from high pressure to low pressure areas. Convergence of air produces low atmospheric pressure and divergence produces high pressure.

Atmospheric stability is the tendency of a parcel of air to remain in place or change its vertical position. The atmosphere is unstable if air parcels rise until they read air of similar temperature and density. Severe weather is associated with unstable air.

Winds blowing over long distances curve because the Earth rotates beneath the atmosphere. Called the Coriolis effect, this curvature is to the right in the Northern Hemisphere. Wind patterns are controlled by horizontal changes in atmospheric pressure, the Coriolis effect, and for surface winds, friction.

Boundaries between cooler and warmer air masses, called fronts, are descried as either cold, warm, stationary, or occluded. Many thunderstorms, tornadoes, snow storms, ice storms, and dust storms are associated with fronts.

Rain storms with lightning and thunder, called thunderstorms, form where there is moist air in the lower troposphere, rapid cooling of rising air, and updrafts to create cumulonimbus clouds. Thunderstorm development proceeds through cumulus, mature, and dissipative stages. Most thunderstorms form during maximum daytime heating, either as individual air mass storms, or as lines or clusters of storms associated with fronts.

Severe thunderstorms have winds over 93 km (58 mi.) per hour, hail diameters greater than 1.9 cm (0.75 in.), or a tornado. Hail forms by ice added in layers onto ice pellets that rise and fall within a storm. Severe thunderstorms form where there is strong vertical wind shear, uplift of air, and dry air above moist air. Downdrafts in severe thunderstorms create gust fronts and microbursts that can cause local damage. Three major types of severe thunderstorms include clusters of storms referred to as multiple convective systems (MCSs), linear squall lines, and large individual storms called supercells. MCSs can produce derechos, straight-line windstorms that are as damaging as tornadoes. Squall lines develop ahead of cold fronts and along drylines, air-mass boundaries similar to fronts. Supercell thunderstorms produce the strongest tornadoes.

Tornadoes are generally funnel-like columns of rotating winds of 65 to over 450 km (40 to over 280 mi.) per hour that extend downward from a cloud to the ground. With diameters in tens of meters, these storms usually travel at 50 km (30 mi.) per hour from southwest to northeast. Tornadoes form by wind shear in severe thunderstorms, especially supercells, and are most common in the central United States. Damage by tornadoes is rated on the Enhanced Fujita (EF) Scale, with EF5 the most severe. Waterspouts are generally weaker tornadoes forming under fair-weather conditions along ocean coastlines and over lakes.

Lightning is an underestimated safety hazard associated primarily with thunderstorms. Large differences in electrical charge develop within a thunderstorm cloud or between the cloud and the ground. Flow of electrical charges within the cloud, or between the ground and the cloud, produce lightning. Electrical current from a lightning strike can move through the ground and kill or disable people.


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Blizzards are severe winter storms in which large amounts of falling or blowing snow reduce visibilities for extended periods of time. Most blizzards are produced by extratropical cyclones that have crossed the Rocky Mountains or have moved along the East Coast as nor’easters. Safety during cool and cold weather is based on the wind chill temperature, a combination of air temperature and wind speed.

Ice storms occur with prolonged freezing rain along a stationary or warm front, below-freezing temperature, and a shallow layer of cold air at the surface. Sleet and snow occur where there is a progressively greater thickness of cold air at the surface.

Weather conditions such as a dust storm or fog can greatly reduce visibility, resulting in deadly accidents. Fog is simply a cloud in contact with the ground. Other hazardous weather conditions include sand storms, mountain windstorms, drought, and heatwaves. Drought and heatwaves are often linked to high-pressure centers that stagnate over regions for extended periods of time. Heatwaves are intensified in cities because of the urban heat island effect. Safety in hot weather requires knowing the heat index, a combination of air temperature and relative humidity. Severe weather produces the much-feared tornadoes and hurricanes (see Chapter 10), but it is heatwaves and blizzards that continue to cause the majority of human deaths from weather phenomena.

Potential human interactions with weather and its hazards are varied. At the local level, land use such as type of housing, landscaping, and agricultural practices may increase the effect of severe weather. On the global scale, atmospheric warming in response to burning of fossil fuels is changing our planet’s weather systems. This warming of both the atmosphere and oceans may feed more energy into storms, potentially increasing the incidence of severe weather events.

Minimizing hazards associated with severe weather such as thunderstorms, tornadoes, heatwaves, droughts, blizzards, and ice storms requires a multifaceted approach. This approach should include the following: (1) more accurate prediction that leads to better forecasting and warnings; (2) mitigation techniques designed to prevent or minimize death and loss of property, such as constructing buildings to better withstand severe weather; (3) hazard preparedness, such as short-term activities that individuals and communities can take once they have been warned of severe weather; and (4) education and insurance programs to reduce risk.

Answers to review questions 1. Describe the difference between, force, work, and power. (p. 283)

In physics, force is that which can cause a mass to accelerate. It may be experienced as a lift, a push, or a pull. Work is done when a force is applied to an object and that object moves a given distance in the direction of the applied force. The rate at which the work is done is power, or in other words, power is energy divided by time.

1. What are the three types of energy? How do they differ from each other? (p. 283)

http://en.wikipedia.org/wiki/Physics

http://en.wikipedia.org/wiki/Mass

http://en.wikipedia.org/wiki/Acceleration


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The three main types of energy are potential energy, kinetic energy, and heat energy. Potential energy is stored energy. Kinetic energy is the energy of motion. Heat energy is the energy of random motion of atoms and molecules.

2. What is the difference between sensible heat and latent heat? (p. 283)

Two types of heat that are important in atmospheric processes are sensible heat, heat that might be sensed or monitored by a thermometer, and latent heat, the amount of heat that is either absorbed or released when a substance changes phase, as from a solid to a liquid, for example.

3. What are the three types of heat transfer? How do they differ from each other? (pp.

283–284)

The three major heat-transfer processes are conduction, convection, and radiation. Conduction is the transfer of heat through a substance by means of atomic or molecular interaction. This process relies on temperature differences, causing heat to flow through a substance from an area of greater temperature to an area of lesser temperature. Convection is the transfer of heat by the mass movement of a fluid, such as water or air. Radiation refers to wavelike energy that is emitted by any substance that possesses heat.

4. Describe how the Earth’s energy balance works. (p. 284)

Earth’s energy balance refers to the general equilibrium between incoming and outgoing energy. The Earth receives energy from the Sun, and this energy affects the atmosphere, oceans, land, and living things before being radiated back into space.

5. What is electromagnetic energy? How are the different types of electromagnetic

energy distinguished? (p. 284)

Electromagnetic energy is a type of radiation that travels through the vacuum of space at the speed of light. The various types of electromagnetic radiation are distinguished by their wavelengths.

6. List the following types of electromagnetic energy in order from shortest wavelength

to longest wavelength. Radio waves, ultraviolet radiation, gamma radiation, visible light, infrared radiation, x-rays, and microwaves. (pp. 284–285)

From shortest to longest: gamma radiation, x-rays, ultraviolet radiation, visible light, infrared radiation, microwaves, and radio waves.

7. Explain why the Sun radiates 16 times more energy than the Earth. (p. 286)


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Hot objects radiate more energy than cold objects. Also, hot objects radiate this energy at shorter wavelengths than cold objects.

8. How is color related to energy absorption? (p. 286)

Dark-colored objects absorb more energy than light-colored objects because they have a lower albedo, or reflectivity, of the surface.

9. Describe the characteristics of the troposphere. How do meteorologists identify the

top of the troposphere? (pp. 286–287)

The troposphere is the lowest of the five major layers, or spheres, of Earth’s atmosphere. Extending about 8 to 16 km (5 to 10 mi.) above the surface of the earth, the defining characteristic of the troposphere is a rapid upward decrease in temperature and its most visible feature is abundant condensed water vapor in the form of clouds.

10. What is the tropopause? How high is it above the Earth’s surface? (p. 287)

The upper boundary of the troposphere is known as the tropopause. Not even the highest mountains breach this upper boundary of the troposphere.

11. Why does atmospheric pressure decrease with increasing altitude? (p. 288)

Since atmospheric pressure is the weight of the column of air that is above any given point, atmospheric pressure is greater at sea level than at the top of a high mountain where there is less air above the surface.

12. What is the difference between stable and unstable air? (p. 290)

An air mass is stable if parcels of air within it resist vertical movement or return to their original position after they have moved. Alternatively, an air mass is considered unstable if parcels within it are rising until they reach air of similar temperature or density.

13. Explain the Coriolis effect. How does it influence weather? (pp. 292–293)

Winds blowing over long distances curve because the Earth rotates beneath the atmosphere. Called the Coriolis effect, this curvature is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Both surface winds and winds in the upper troposphere are influenced by the Coriolis effect.

14. What conditions are necessary for a thunderstorm to form? A severe thunderstorm?

(pp. 295–296)


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Three basic conditions are necessary for a thunderstorm to form: (1) Water vapor must be available in the lower atmosphere to feed clouds and precipitation as the storm forms; (2) A steep vertical temperature gradient must exist in the environment so that the rising air becomes warmer than the air through which it is moving. This gradient places colder air over warmer, moist air; (3) An updraft must force moist air up to colder levels of the atmosphere. Conditions necessary for the formation of a severe thunderstorm include large changes in wind velocity and direction producing wind shear, high water-vapor content in the lower troposphere, uplift of air, and the existence of a dry air mass above a moist air mass. In general, the greater the vertical wind shear, the more severe that a thunderstorm will become.

15. Describe the three stages of thunderstorm development. (pp. 295–296)

Thunderstorm formation starts as moist air is forced upwards, cools, and water vapor condenses to form a puffy cumulus cloud. As the clouds domes and towers grow upward, precipitation starts by one of two methods: (1) Growth of the cloud into colder air causes water droplets to freeze into ice crystals and snowflakes. The larger snowflakes fall until they enter air that is above freezing and melt to form raindrops. (2) Large droplets collide with smaller droplets in warm air in the lower part of the cloud and coalesce to become raindrops. Once these raindrops are too large to be supported by updrafts in the cloud, they begin to fall, creating a downdraft. The mature stage of thunderstorm development begins when the downdraft and falling precipitation leave the base of the cloud. The storm now has both updrafts and downdrafts, and it continues to grow until it reaches the top of the unstable atmosphere. During this stage, the storm produces heavy rain, lightning and thunder, and occasionally hail. The dissipative stage begins when the upward supply of moist air is blocked by downdrafts at the lower levels of the cloud, causing some of the falling precipitation to evaporate. Deprived of moisture, the thunderstorm weakens, precipitation decreases, and the cloud dissipates.

16. What are supercells, mesoscale convective complexes, and squall lines? How do they

differ? Why are they significant natural hazards? (p. 298)

Three types of severe thunderstorms have been identified on the basis of their organization, shape, and size. They include roughly circular clusters of storm cells called mesoscale convective systems, linear belts of thunderstorms called squall lines, and large cells with single updrafts called supercells. Downbursts from severe thunderstorms can generate strong, straight-line windstorms, producing


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severe, tornado-strength wind gusts. These winds can cause numerous trees to fall, widespread power outages, serious injuries, and multiple fatalities.

17. What is hail? How does it form? Where is it most common in the United States? (p.

300)

Hail starts with a small ice pellet as a nucleus and receives a coating of liquid water in the lower part of the storm. That coating freezes when a strong updraft carries the stone upward into cold air. This process is repeated many times to form a large piece of hail. In North America, hailstorms are most common in the Great Plains, particularly in northeastern Colorado and southeastern Wyoming.

18. Characterize a tornado in terms of wind speed, size, typical speed of movement,

duration, and length of travel. (pp. 300–301)

Tornadoes typically have diameters measured in tens of meters and wind speeds of 65 km (40 mi.) to more than 450 km (280 mi.) per hour. Once they touch down, tornadoes usually travel 6 to 8 km (4 to 5 mi.) and last only a few minutes before weakening and disappearing.

19. Describe the five stages of tornado development. (p. 301)

In the initial organizational stage, wind shear causes rotation to develop within the thunderstorm. Major updrafts lower a portion of the cumulonimbus cloud and form a wall cloud. This wall cloud may begin to slowly rotate and a short funnel cloud may descend. A tornado has formed if dust and debris on the ground begin to swirl below the funnel. In the second, mature stage, a visible condensation funnel extends from the thunderstorm cloud to the ground as moist air is drawn upward. In stronger tornadoes, smaller intense whirls called suction vortices may form within the larger tornado. The suction vortices orbit the center of the large tornado vortex and appear to be responsible for its greatest damage. When the supply of warm moist air is reduced, the tornado enters the shrinking stage. In this stage, it thins and begins to tilt. As the width of the funnel decreases, the winds can increase, making the tornado more dangerous. In the final decaying, or rope stage, the upward-spiraling air comes in contact with downdrafts and the tornado begins to move erratically. A tornado can still be extremely dangerous at this point.

20. What is a blizzard? How does a blizzard develop? (pp. 302–304)


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Blizzards are severe winter storms in which large amounts of falling or blowing snow are driven by high winds to create low visibilities for an extended period of time. Storms producing heavy snowfall and blizzards form from an interaction between upper-level winds associated with a low-pressure trough and a surface low-pressure system. High winds picking up previously fallen snow create a ground blizzard.

21. What is a nor’easter? How is it related to blizzards? (p. 304)

Storms that move along the east coast of the United States and Canada are called nor’easters. These storms have hurricane-force winds, heavy snows, intense precipitation, and high waves that can damage coastal areas.

22. Describe the weather conditions that cause an ice storm. (pp. 304–306)

These storms typically develop during the winter in a belt on the north side of a stationary or warm front. In this setting, a combination of three conditions lead to freezing rain: (1) an ample source of moisture in the warm air mass south of the front; (2) warm air uplifted over a shallow layer of cold air; and (3) objects on the land surface at or very close to freezing. Under these conditions snow begins to fall from the cooled top of the warm air mass. The snow melts as it passes through the warm air and the resulting raindrops become supercooled when they hit the cold air at the surface. Upon contact with cold objects, the rain immediately freezes to form a coating of ice.

23. How are the heat index and wind chill temperature alike? How are they different?

When is each of these indices important? (pp. 304, 311–312)

The wind chill effect takes place when moving air rapidly cools exposed skin by evaporating moisture and removing warm air from next to the body. The heat index measures the body’s perception of air temperature, which is greatly influenced by humidity. While a higher wind chill can reduce the time it takes for frostbite to form, the heat index measures conditions that can lead to heat stress. Both are important tools that can indicate unsafe outdoor conditions.

24. How is global warming expected to affect severe weather? (p. 312)

On the basis of computer models, atmospheric scientists conclude that global warming is very likely to increase the heat index and number of heatwaves over land and the intensity of precipitation events in most areas. The computer models also indicate that global warming is likely to increase the risk of drought in midlatitude continental interiors and increase wind and precipitation intensities in hurricanes, typhoons, and other tropical cyclones.

25. What are some natural service functions of severe weather? (p. 313)


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The natural service functions of severe weather are often long term. Lightning is the primary ignition source for natural wildfires, which are a vital process in prairie, tundra, and forest ecosystems. Windstorms and ice storms help maintain the health of forests by toppling dead and diseased trees, which are then recycled in the soil. Blizzards and other snow storms, thunderstorms, and tropical storms are important sources of water. Snowmelt and seasonal rainfall reduces a region’s vulnerability to drought. Weather also has aesthetic value, gives many people excitement, and can even become a tourist draw, as in the hobby of tornado chasing.

26. What is the difference between a severe weather watch and warning? (p. 313)

A watch warns the public of the possibility of severe weather developing in the near future, while a warning indicates that the area affected is in danger, and people should take immediate action to protect themselves and others. Watches may be upgraded to warnings, or warnings may be issued for an area not previously under a watch.

27. How do preparedness planning and mitigation differ? (p. 318)

Establishing community and individual plans and procedures to deal with an impending natural hazard is considered preparedness. On the other hand, long-term actions to prevent or minimize death, injuries, and damage are considered mitigation.

28. Explain how drought, soil moisture, and a heatwave can be interrelated. (pp. 311–

312)

Drought is an extended period of unusually low precipitation that produces a temporary shortage of water for people, animals, and plants; heatwaves are prolonged periods of extreme heat that are both longer and hotter than normal; while soil moisture refers to the amount of moisture in the soil. Drought, with its accompanying clear skies, allows solar radiation to heat the ground and dry out the soil. As soil moisture decreases, there is less water to evaporate and cool the air. Heat buildup in the soil than radiates back into the atmosphere to significantly warm temperatures, causing a heatwave.

29. What causes the urban heat island effect? How can this effect be mitigated? (p. 312)

The urban heat island effect is a local climactic condition where a metropolitan area may become as much as 12˚C (22˚F) warmer than the surrounding countryside. Methods to reduce the effect include increasing the reflectivity of urban surfaces, increasing the amount of pervious pavement to provide the air access to moisture in the soil, and adding vegetation to urban areas.


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Answers to Critical Thinking Questions: 1. What severe weather events are potential hazards in the area where you live? What

are some steps you might take to protect yourself from such hazards? Which of these hazards is your community least prepared for?

Varies with region.

2. Lightning is the deadliest weather hazard and the one that is likely to affect many

people. Use the Web resources in the next section to:

a. explain why news reports about “survivors” might be misleading. People who are close to a lightning strike but not actually struck may think they have been hit. Also, being hit may cause memory loss.

b. determine when you need to take shelter from lightning and how long you

should stay in the shelter.

You should take shelter as soon as the storm is close, keeping in mind that the leading edges of thunderstorms often have frequent lightning. You should stay in the shelter until the storm passes.

c. determine what behaviors outside and inside your house increase the

possibility that you might be struck by lightning.

You will increase your risk of being struck if you are in an open field, or under a tall tree. Also, carrying metal objects, or objects that carry an electrical charge, can increase your chances of being hit. Inside, you have a higher risk of being hit next to plumbing, electrical wires, or near windows. If your house is not grounded, the chances of being hit are much higher.

d. explain how people living in Florida are very likely to be affected by lightning

strikes.

Florida has more thunderstorms and lightning than other places, for instance Maine. Therefore, chances of being hit are higher in Florida.

3. Tornadoes can often be spotted on weather radar, whereas many other clouds cannot.

What makes tornadoes visible?


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Tornadoes can be seen on Doppler radar, as in places where one part of a cloud is moving toward the radar, and an adjacent part is moving rapidly away from the radar.

4. Study the diagrams of cold fronts and warm fronts, and read the description about the

development of ice storms. Explain why sleet (small pellets of ice) is more likely to accompany cold fronts than freezing rain.

Ice storms occur with prolonged freezing rain along a stationary or warm front, below-freezing temperature, and a shallow layer of cold air at the surface. Sleet and snow occur where there is a progressively greater thickness of cold air at the surface. Therefore, as cold fronts push a thickening wedge of air along the surface, sleet forms as the water droplets move through colder air. In warm fronts, the precipitation falls through progressively warming air, and rain results.

5. Why does hail form in thunderstorms and not in other rainstorms or snowstorms?

Hail forms in situations where strong vertical temperature gradients and updrafts carry the ice to high levels of the atmosphere. In other storms, the winds, updrafts, and temperature gradients are not strong enough.

6. Has your community ever experienced a heat wave? If so, when did it occur and how

were people affected? Does your community have a heat health warning system? If so, what actions do local officials and emergency personal take when the system is activated? If not, what type of system would you recommend? What actions could you take to mitigate the effects of a heatwave on your living conditions?

Answers vary by region.

Suggested Activities 1. Plot hurricane paths across the globe during hurricane season. 2. Take photos of different types of storm clouds, and discuss in class. 3. Take two large soda bottles, and fill one with water. Tape the bottles together, and

turn upside down and watch tornado-like features develop. Discuss formation of tornadoes.


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Additional Resources (media, films, articles, journals, web sites) Print Resources Abbott, P.L., 2012, Natural Disasters, 8th ed., McGraw Hill, Boston, 512 pp. Eldredge, N., 1998, Life in the Balance, Princeton University Press, Princeton, 224 pp. Griggs, G.B., and Gilchrist, J.A., 1983, Geologic Hazards, Resources, and

Environmental Planning, Wadsworth Publishing Co., Belmont, CA, 502 pp. Keller, E.A., 2000, Environmental Geology, Eighth Ed., Prentice Hall, Englewood Cliffs,

N.J., 562 pp. Kusky, T.M., 2004, Encyclopedia of Earth Science, 528 pages, Facts on File, New York,

ISBN 0816049734. Kusky, T.M., 2003, Geological Hazards; A Sourcebook. 300 pp. An Oryx Book. Greenwood Press, Westport Conn., ISBN 1-57356-469-9. Mackenzie, F.T., and

Mackenzie, J.A., 1995, Our Changing Planet, An Introduction to Earth System Science and Global Environmental Change, Prentice Hall, Englewood Cliffs, N.J., 387 pp.

Organizations Dealing with Coastal and Weather Hazards Congressional Natural Hazards Work Group is a cooperative endeavor between a group of private and public organizations, whose goal is to develop a wider understanding within Congress of the value of reducing the risks and costs of natural disasters. Information on the Natural Hazards Caucus Work Group can be found at: http://www.agiweb.org/gap/workgroup/legislation109.html. Some of the lead organizations include the American Meteorological Society and University Corporation for Atmospheric Research (http://www.ucar.edu), and the National Science Foundation (http//www.nsf.gov). Federal Emergency Management Agency FEMA 500 C Street SW Washington D.C. 20472 Phone 202-646-4600 http://www.fema.gov FEMA is the nation’s premier agency that deals with emergency management and preparation, and issues warnings and evacuation orders when disasters appear imminent. FEMA maintains a web site that is updated at least daily, includes information of hurricanes, floods, fires, national flood insurance, and information on disaster prevention, preparation, emergency management. Divided into national and regional sites. Also contains information on costs of disasters, maps, and directions on how to do business with FEMA.

http://www.fema.gov/


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U.S. Geological Survey U.S. Department of the Interior 345 Middlefield Road Menlo Park, CA 94025 650-329-5042 also, offices in Reston, VA, Denver, CO http://www.usgs.gov/ The USGS is responsible for making maps of the many of the different types of hazards

discussed in this book, including earthquake and volcano hazards, tsunami, floods, landslides, and radon.

http://www.usgs.gov/corecast/?tag=weather CoreCast is the USGS site for Natural Science from the inside out.

National Oceanographic and Atmospheric Association (NOAA) http://www.noaa.gov/ NOAA conducts research and gathers data about the global oceans, atmosphere, space and sun, and applies this knowledge to science and service that touch lives of all Americans. NOAA’s mission is to describe and predict changes in the Earth’s environment, and conserve and wisely manage the nation’s coastal and marine resources. NOAA’s strategy consists of seven interrelated strategic goals for environmental assessment, prediction, and stewardship. These include 1) advance short-term warnings and forecast services, 2) implement season to interannual climate forecasts, 3) assess and predict decadal to centennial change, 4) to promote safe navigation, 5) to build sustainable fisheries, 6) to recover protected species, and 7) to sustain healthy coastal ecosystems. NOAA runs a web site that includes links to current satellite images of weather hazards, issues warnings of current coastal hazards and disasters, and has an extensive historical and educational service.

The National Hurricane Center http://www.nhc.noaa.gov/ is a branch of NOAA, and posts regular updates of hurricane paths and hazards. Non-Print Sources Dealing with Coastal and Weather Hazards http://edcwww.cr.usgs.gov/ EROS Data Center, lists satellite images, land cover maps, elevation models, maps, and aerial photography useful for Natural Hazards Studies. NASA’s web site on natural hazards: http://earthobservatory.nasa.gov/NaturalHazards/ NASA’s Earth observatory lists satellite images of natural hazards including dust, smoke, fires, floods, severe storms, and volcanoes. USGS web site for natural hazards:


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http://www.usgs.gov/natural_hazards/ USGS activities in the hazards theme area deal with describing, documenting, and understanding natural hazards and their risks. The web page contains explanations of individual hazards, geographic distribution of hazards, and fact sheets on hazards. They also have links describing USGS involvement in recent hazards. http://www.accuweather.com/index.asp WeatherMatrix is a worldwide organization of over 3000 amateur and professional weather enthusiasts—meteorologists, storm chasers and spotters, and weather observers—from all parts of the globe. WeatherMatrix was formerly the Central Atlantic Storm Investigators (CASI). Has frequently updated news about weather-related disasters. Natural Hazards Observer http://www.colorado.edu/hazards/o/ This web site is the on-line version of the periodical, The Natural Hazards Observer. It contains features about various hazards and disasters. It also provides information of emergency management, research, politics, and education of natural disasters.


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Chapter 10 Hurricanes and Extratropical Cyclones Learning Objectives Hurricanes, and their mid-latitude relative, extratropical cyclones, are the most powerful storms on Earth and among the most deadly and costly of natural hazards—Hurricane Katrina alone was the most expensive natural disaster in history. Called cyclones, these storms affect parts of the United States and Canada daily and are responsible for most severe weather. Understanding how these storms work helps us appreciate how they pose a threat to our highly technological society. As our climate changes and sea level rises, these storms will pose a greater hazard to coastal regions. Despite this threat, government flood insurance and disaster relief policies continue to encourage development in hurricane-prone regions. As Hurricane Katrina demonstrated, choices made by individuals, businesses, and government officials on how to prepare for and respond to hurricanes can turn an “Act of God” into an “Act of Man.” Your goals in reading this chapter should be to

• understand the weather conditions that create, maintain, and dissipate cyclones.

• understand the difficulties in forecasting cyclone behavior. • know what geographic regions are at risk for hurricanes and extratropical

cyclones. • understand the effects of cyclones in coastal and inland areas. • recognize the linkages between hurricanes, extratropical cyclones, and other

natural hazards. • recognize linkages between cyclones and other natural hazards. • know the benefits derived from cyclones. • understand the adjustments that can be made to minimize damage and

personal injury from coastal cyclones. • know the prudent actions to take for hurricane or extratropical cyclone

watches and warnings. Chapter Outline 10. Hurricanes and Extratropical Cyclones

10.1. Introduction to Cyclones Survivor Story 10.1: Hurricane Katrina


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10.1.1. Classification 10.1.2. Naming

10.2. Cyclone Development 10.2.1. Tropical Cyclones 10.2.2. Extratropical Cyclones

10.3. Geographic Regions at Risk for Cyclones 10.4. Effects of Cyclones

10.4.1. Storm Surge 10.4.2. High Winds 10.4.3. Heavy Rains

10.5. Linkages between Cyclones and Other Natural Hazards 10.6. Natural Service Functions of Cyclones 10.7. Human Interaction with Cyclones 10.8. Minimizing the Effects of Cyclones

10.8.1. Forecasts and Warnings 10.8.1.1. Hurricane Forecasting Tools Case Study 10.2: Hurricane Intensity and Warm Seas 10.8.1.2. Storm Surge Predictions Professional Profile 10.3: The Hurricane Hunters 10.8.1.3. Hurricane Prediction and the Future

10.9. Perception of and Adjustment to Cyclones 10.9.1. Prediction of Cyclones 10.9.2. Adjustment to Hurricanes and Extratropical Cyclones

Chapter Summary Cyclones, large areas of low atmospheric pressure with winds converging toward the center, are associated with most severe weather. Because of the Coriolis effect, winds blow counterclockwise around cyclones in the Northern Hemisphere.

Cyclones are described as either tropical or extratropical based on their characteristics and origin. Tropical cyclones have warm central cores, are not associated with weather fronts, and form between 5˚ and 20˚ latitude over tropical and subtropical oceans. Called either typhoons or cyclones in most of the Pacific and Indian Oceans, these storms are referred to as hurricanes in the Atlantic and northeast Pacific Oceans and in this book. Extratropical cyclones have cool central cores, develop along weather fronts, and form between 30˚ and 70˚ latitude over either the land or ocean. These midlatitude cyclones produce coastal windstorms, snowstorms, blizzards, and severe thunderstorm outbreaks. Both types of cyclones can have high-velocity straight-line winds, tornadoes, heavy precipitation, and coastal storm surges.

Tropical cyclones are classified by their prevailing wind speed and are referred to as tropical depressions, tropical storms, and hurricanes with increasing wind speed. Tropical storms must have sustained winds of at least 119 km (74 mi.) per hour to


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become a hurricane. A hurricane is assigned a category on the Saffir-Simpson Hurricane Scale based on measured or inferred sustained winds. Hurricanes reaching Category 3 or above are considered major hurricanes. Tropical storms and hurricanes are given women’s or men’s names from internationally agreed upon lists for the region where they form. Extratropical cyclones are sometimes named for their geographic area of origin or prevailing wind direction.

Most tropical cyclones start out as a tropical disturbance, a large thunderstorm complex associated with a low-pressure trough. In the Atlantic Ocean, many of these disturbances form off the west coast of Africa as easterly waves in the trade winds. A tropical disturbance that develops a circular wind-circulation pattern becomes a tropical depression and may become a tropical storm if its winds exceed 63 km (39 mi.) per hour. Only a few tropical storms encounter the environmental conditions needed to become a hurricane, that is, waters that are at least 26˚C (80˚F) to a depth of 46 m (150 ft.); uninhibited convection for moist air evaporating from the sea surface; and weak winds aloft that keep vertical wind shear to a minimum.

Hurricanes develop spiraling rain bands of clouds around a nearly calm central eye. The eye is surrounded by an eye wall cloud that has the storm’s strongest winds and most intense rainfall. Warm, moist air condensing in rain bands and the eye wall releases latent heat and provides continual energy from the hurricane. Excess heat is vented out of the storm’s top. Most hurricanes move forward at 19 to 27 km (12 to 17 mi.) per hour steered by winds in the idle and upper troposphere and generally lose intensity over land or cooler water.

Extratropical cyclones typically form along fronts where there are strong, diverging winds in the upper troposphere and along surface boundaries, such as a shoreline or a mountain front. Upper troposphere winds are strongest in polar and subtropical jet streams. Extratropical cyclones often intensify as they move east from the Rocky Mountains or along a coastline. In North America, most extratropical cyclones have a cold front trailing to the southwest and a warm front to the east. Cold air circulating around these cyclones collides with warm air rising in the eastern part of the storm. Many mature anticyclones develop an occluded front and a large, comma-shaped cloud formation before they dissipate.

In North America, the Gulf and East coasts are at highest risk for tropical cyclones. Hurricane-strike probabilities are the greatest in southern Florida, the northern Gulf Coast, and Cape Hatteras. Extratropical cyclones are the primary severe weather hazard on the Pacific Coast and cause storms on the Great Lakes. Nor’easters, named for their strong northeasterly winds, are a hazard for the eastern United States and Atlantic Canada.

Cyclones produce coastal storms surges, high winds, and heavy rains. Major hurricanes and intense extratropical cyclones generate storm surges over 3 m (10 ft.) from water piled up by high winds. Higher surges are produced by larger, more intense, or faster moving storms, and on shallow coastlines or narrow bays. In the Northern Hemisphere, the greatest storm surge, highest winds, and most tornadoes are in the right forward quadrant of tropical cyclones. Much of the structural damage from coastal storms comes from wind-driven waves on top of the storm surge. Strong currents from storm surges cut channels through islands and peninsulas and deposit sand as overwash. Wind


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damage from hurricanes is more widespread, but less deadly than the storm surge. Although hurricanes hold most rainfall records, tropical storms also produce intense rains and flooding. Coastal cyclones generally cause both saltwater and freshwater flooding. Inland flooding occurs from hurricane remnants if storms move slowly, encounter hills or mountains, interact with other weather systems, or track over previously saturated ground.

Cyclones are closely linked with other severe weather, flooding, landslide, and debris flow hazards. The hazard posed by storm surge and erosion from coastal cyclones will increase as sea level rises worldwide from global warming. Hurricane intensity is also projected to increase with warmer global temperatures. Tropical storms and coastal extratropical cyclones will become more destructive to our society as coastal populations and per capita wealth grows. On the positive side, cyclones are major sources of precipitation, help maintain global heat flow, and contribute to long-term ecosystem health.

Accurate forecasts, effective storm warnings, strict building codes, and well-planned evacuations can minimize the effects of coastal cyclones. Hurricane forecasting relies on weather satellites, aircraft flights, Doppler radar, and automated weather buoys. Computer models predict hurricane tracks more accurately than their intensity. Storm surge predictions are based on wind speed, fetch, average water depth, and timing of landfall in relation to astronomical tides.

Perception of the coastal cyclone hazard depends on individual experience and proximity to the hazard. Community adjustments to hurricanes in developed countries involve building protective structures or modifying people’s behavior through land-use zoning, evacuation procedures, and warning systems. Individual adjustments to hurricanes include having emergency supplies on hand, preparing once a storm prediction is made, and if required, evacuating before the storm hits. Homes can be constructed to withstand hurricane-force winds and elevated to allow passage of storm surges.

Answers to Review Questions: 1. Describe the characteristics of a cyclone. What distinguishes a tropical cyclone from

an extratropical cyclone? (pp. 331–333)

A cyclone is an area or center of low atmospheric pressure characterized by rotating winds. A tropical cyclone forms over warm tropical or subtropical ocean water, typically between 5˚ and 20˚ latitude. They are not associated with fronts and have warm central cores. Extratropical cyclones develop over land and water, typically between 30˚ and 70˚ latitude, are generally associated with fronts, and have cool central cores. Both types of cyclones are characterized by their intensity, which is indicated by their sustained wind speeds and lowest atmospheric pressure.


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2. How do tropical cyclones, hurricanes, tropical storms, tropical depressions, tropical disturbances, and typhoons differ? (pp. 331–335)

A tropical cyclone is a general term for large thunderstorm complexes rotating around an area of low pressure that has formed over warm tropical or subtropical ocean water. These complexes go by a variety of names depending on their intensity and location. Low-intensity tropical cyclones are called tropical depressions and tropical storms. High-intensity tropical cyclones are called typhoons or cyclones in parts of the Pacific and Indian Oceans, those affecting the United States and Canada are known as hurricanes. Most hurricanes start out as a tropical disturbance, a large area of unsettled weather that is typically 200 to 600 km (120 to 370 mi.) in diameter and has an organized mass of thunderstorms that persists for more than 24 hours. The tropical disturbance may become a tropical depression if winds increase and spiral around the area of disturbed weather to form a low-pressure center. The depression is upgraded to a tropical storm and receives a name when maximum sustained winds increase to 63 km (39 mi.) per hour. If the winds continue to increase in speed, a tropical storm may become a hurricane.

3. Explain how and where hurricanes form and dissipate. (pp. 336–339)

Several favorable environmental conditions must be present to allow a hurricane to form. First, warm ocean waters of at least 26˚C (80˚F) must extend to a depth of 46 m (150 ft.) or more. Second, the atmosphere must cool fast enough from the surface upward to allow moist air to continue to be unstable and convect. Finally, there must be very little vertical wind shear between the surface and the top of the troposphere. Hurricanes obtain their energy from the evaporation and subsequent condensation of warm or subtropical sea water and generally lose strength when they move over land.

4. What are the conditions necessary for hurricane formation? (p. 339)

Hurricane development is favored where (1) there is a thick layer of warm water at the sea surface; (2) warm, moist air is free to rise upward toward the top of the troposphere; and (3) upper-level winds are relatively weak.

5. How does the Coriolis effect influence hurricane winds and movement? (p. 331)

The Coriolis force helps initiate the spinning of the thunderstorms around the center of a tropical disturbance.

6. What parts of a hurricane have the most intense winds, rainfall, tornadoes, and storm

surge in the Northern Hemisphere? (p. 336)

The northeast quadrant has the most intense wind and storm surge.


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7. How are hurricanes categorized? Which categories are considered major hurricanes?

Which category is most intense? (p. 335)

Hurricanes are classified by their wind speed on a damage-potential scale known as the Saffir-Simpson scale. It is divided into five categories based on the highest 1-minute average wind speed in the storm. Meteorologists describe Category 3 through 5 hurricanes as major hurricanes. Category 5 hurricanes are the most intense.

8. Which areas of the United States and Canada have the highest risk for hurricanes?

(pp. 342–345)

The East and Gulf Coasts of the United States have the highest risk for tropical storms and hurricanes in North America.

9. Where are tropical cyclones most common? (pp. 342–345)

Tropical cyclones have the greatest impact on coastal areas with warm offshore waters, such as the Gulf of Mexico and the Gulf Stream along the East Coast.

10. Describe or sketch the three typical paths taken by Atlantic hurricanes affecting North

America. (pp. 342–345)

Most hurricanes that threaten the East and Gulf coasts form off the west coast of Africa and take one of three tracks:

1. Westward toward the east coast of Florida, sometimes passing over

Caribbean islands such as Puerto Rico and the Virgin Islands; these storms then move out into the Atlantic Ocean to the northeast without striking the North American continent.

2. Westward over Cuba and into the Gulf of Mexico to strike the Gulf Coast.

3. Westward to the Caribbean and then northeastward skirting the East Coast;

these storms may strike the continent from central Florida to New York. A few storms continue north as hurricanes to strike coastal New England or Atlantic Canada.

11. Describe the similarities and differences between the effects of tropical and

extratropical cyclones. (p. 345)

Although the destructive effects of tropical and extratropical cyclones can be similar, the two types of storms differ in their source of energy and structure. Tropical cyclones derive energy from warm ocean water and the latent heat that


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is released as rising air condenses to form clouds. Extratropical cyclones obtain their energy from the horizontal temperature contrast between air masses on either side of a front.

12. What are three major causes of hurricane damage? Which is typically the most

deadly? (p. 345)

Storm surge, high winds, and heavy rains are especially damaging effects of hurricanes. Storm surge causes the greatest damage and contributes to 90 percent of all hurricane-related fatalities.

13. Explain the causes and effects of storm surge. What will cause a storm surge to

increase? (p. 346)

Storm surge is the local rise of sea level that results primarily from offshore winds pushing water toward the coast. Larger, more intense, or faster moving hurricanes create higher storm surges. Higher storm surges also develop on broad, shallow coastlines where wind-driven water slows down from friction with the ocean bottom. Most of the storm surge damage comes from large storm waves that are superimposed upon the surge. These storm waves, combined with ocean currents, erode beaches, islands, and roads.

14. Describe the changes that occur when a hurricane moves inland and becomes an

extratropical cyclone. (p. 347)

Wind speeds in most hurricanes diminish exponentially once they make landfall. However, if a dying hurricane merges with an upper-level extratropical cyclone or cold front, or if it rapidly moves from warm to cold water, it can become an extratropical cyclone. During the transition some of these storms can maintain or even increase their wind speed.

15. Describe the similarities and differences between tropical storms and hurricanes. (p.

336)

Both have heavy rainfall, but hurricanes have sustained winds of over 74 mph, and consist of a mass of thunderstorms rotating about a central low.

16. How will global warming and population trends interact with cyclones in coastal

areas? (p. 349)

Global warming is expected to generate stronger hurricanes, and more of them. More and more people are moving into coastal areas, so the costs of hurricanes


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in terms of damage and lost lives is expected to increase dramatically over the next decade.

17. Explain how cyclones are linked with other natural hazards. (p. 349)

The effects of cyclones are magnified by linkages to other natural hazards. Cyclones are closely linked to coastal erosion, flooding, mass wasting, and other types of severe weather, such as tornadoes, severe thunderstorms, snowstorms, and blizzards. Some of the fastest rates of coastal erosion occur during the landfall of cyclones. Most cyclones making landfall cause both saltwater flooding from a storm surge and freshwater flooding from heavy rains. In mountainous areas, heavy rains associated with cyclones often cause devastating landslides and debris flows. Wind damage from hurricanes is not limited to the winds circulating around the eye of the storm, but also occurs through downbursts of precipitation-driven winds with speed and numerous tornadoes. As global sea level rises because of global warming, storm surges from cyclones will be able to penetrate further inland than ever before.

18. What are the natural service functions of cyclones? (pp. 349–350)

Cyclones, and the weather fronts associated with them, are the primary source of precipitation in most areas of the United States and Canada. In the eastern and southern United States, hurricanes and tropical storms often provide much needed precipitation to moisture-starved areas. Hurricanes also serve an important function in equalizing the temperatures of our planet. Tropical cyclones elevate warm air from the tropics and distribute it toward the polar regions. Cyclones also have important natural service functions in ecosystems. Winds from these storms carry plants, animals, and microorganisms long distances, helping populate volcanic islands with flora and fauna as the islands rise above sea level. Hurricane-generated waves can also stir up deeper, nutrient-rich waters, resulting in plankton blooms in the open ocean and estuaries. Cyclones rejuvenate ecosystems ranging from old-growth forests to tropical reefs. Overall these storms contribute to species diversification in many ecosystems.

19. How do hurricane watches and warnings differ? (p. 351)

A hurricane watch is issued when a hurricane is likely to strike within the next 36 hours, and a hurricane warning is given when the storm is likely to make landfall within the next 24 hours or less.

20. Describe the tools used in making hurricane forecasts. (p. 351)


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Weather satellites are a valuable tool for hurricane detection, since the great storms form over open ocean. Aircraft are invaluable tools, as planes are flown directly into a hurricane to gather data, especially regarding intensity. Doppler radar systems provide another means of collecting data about hurricanes. Radar can reveal information about rainfall, wind speed, and the direction the storm is moving. Weather buoys floating along the Atlantic and Gulf coasts are also used as automated weather stations that continuously record weather conditions at their location. Some information is also obtained from ships that are in the vicinity of the hurricane. Meteorologists use computer models that take into account all available data to make predictions about hurricane tracks.

21. Describe the adjustments that people need to make to survive hurricanes. (pp. 357–

359)

Warning systems, evacuation plans and shelters, insurance, and building design are key adjustments to hurricanes. Emergency warning systems are designed to give the public the maximum possible advance notice that a potential hurricane is headed their way. Efficient evacuation plans must be developed and distributed prior to hurricane season to ensure the most well-organized escape possible. Insurance policies should be available (at appropriate cost) to property holders living in hurricane-prone regions. Homes and other buildings should be constructed to withstand hurricane-force winds and elevated to allow passage of a storm surge. Personal adjustments for shoreline residents of East and Gulf coasts first include being aware of the hurricane season. People should prepare their homes and property by trimming dead or dying branches from trees, obtaining flood insurance, and installing heavy-duty shutters that can be closed to protect windows. They should learn the evacuation routes and discuss emergency plans with their loved ones.

Answers to Critical Thinking Questions: 1. If you had to evacuate your home and go to a nearby public shelter, where would it

be? If you had to evacuate your home and travel at least 160 km (100 mi.) from where you live, where would you go? What would you take with you in either case? What problems might you or your community be faced with in an evacuation (e.g., people in poor health or with disabilities, people without a means of transportation, visitors, pets, domesticated animals)? What would be your concerns?


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Most shelters are in local schools, Red Cross Centers, and in some religious centers. It is best to seek high ground inland from coastal storms for shelter. It is a good idea to have a kit, or a list of things to bring before storms strike; and it should include basic nonperishable food, water, blankets, clothes, radio, batteries, flashlight, and contact information.

2. The southern tip of Florida has a very large area of marsh and swampland, The

Everglades, and a large lake, Lake Okeechobee. Based on your understanding of how a hurricane works, what effect would these wetlands have on a hurricane that was tracking across southern Florida? What effect would the hurricane have on Lake Okeechobee?

The wetlands will offer warm water to the hurricane and not be much different than the open ocean in terms of supplying warm moisture to the storm. However, the storm surge may over run the swamps with salt water, and many grasses and brush trees can be disrupted by the winds.

3. What conditions required for hurricane development could explain why hurricanes

generally do not form between 5˚ N and 5˚ S of the Equator, or in the southeastern Pacific and south Atlantic Oceans?

Strong winds at height shear off the tops of thunderstorms.

4. Obtain a topographic map (see Appendix C) for an ocean beach you visit, or for an urban area along the shore of the Atlantic or Gulf coasts. Shade or color the area that would be affected by a 20-ft. or 5-m storm surge. Examine your completed map and assess the damage that would occur, the routes people would take for evacuation, and land use restrictions you would recommend for future development.

Suggested Activities 1. Plot hurricane paths across the globe during hurricane season. 2. Take photos of different types of storm clouds, and discuss in class. 3. Take two large soda bottles, and fill one with water. Tape the bottles together, and turn

upside down and watch tornado-like features develop. Discuss formation of tornadoes.


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Additional Resources (media, films, articles, journals, web sites) Print Resources Dealing with Coastal and Weather Hazards Abbott, P.L., 2012, Natural Disasters, 8th ed., McGraw Hill, Boston, 512 pp. Eldredge, N., 1998, Life in the Balance, Princeton, Princeton University Press, 224 pp. Griggs, G.B., and Gilchrist, J.A., 1983, Geologic Hazards, Resources, and

Environmental Planning, Belmont, CA, Wadsworth Publishing Co., 502 pp. Keller, E.A., 2000, Environmental Geology, eighth ed., Englewood Cliffs, N.J., Prentice

Hall, 562 pp. Kusky, T.M., 2004, Encyclopedia of Earth Science, Facts on File, New York, 528 pages,

ISBN 0816049734. Kusky, T.M., 2003, Geological Hazards; A Sourcebook, an Oryx Book, 300 pp. Kusky, T.M., 2007, The Coast, Facts on File, Hazardous Earth Set. Mackenzie, F.T., and Mackenzie, J.A., 1995, Our Changing Planet, An Introduction to

Earth System Science and Global Environmental Change, Prentice Hall, Englewood Cliffs N.J., 387 pp.

Nonprint Sources Dealing with Coastal and Weather Hazards http://edcwww.cr.usgs.gov/ EROS Data Center lists satellite images, land cover maps, elevation models, maps, and aerial photography useful for Natural Hazards Studies. NASA’s web site on natural hazards: http://earthobservatory.nasa.gov/NaturalHazards/ NASA’s earth observatory lists satellite images of natural hazards, including dust, smoke, fires, floods, severe storms, and volcanoes. USGS web site for natural hazards: http://www.usgs.gov/natural_hazards/ USGS activities in the hazards theme area deal with describing, documenting, and understanding natural hazards and their risks. The web page contains explanations of individual hazards, geographic distribution of hazards, and fact sheets on hazards. They also have links describing USGS involvement in recent hazards. http://www.accuweather.com/blogs/weathermatrix/ WeatherMatrix is a worldwide organization of over 3000 amateur and professional weather enthusiasts—meteorologists, storm chasers and spotters, and weather observers—from all parts of the globe. WeatherMatrix was formerly the Central Atlantic Storm Investigators (CASI). Has frequently updated news about weather-related disasters. http://www.colorado.edu/hazards/


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This web site is the online version of the periodical, The Natural Hazards Observer. It contains features about various hazards and disasters. It also provides information on emergency management, research, politics, and education on natural disasters. Organizations Dealing with Coastal and Weather Hazards Congressional Natural Hazards Work Group is a cooperative endeavor between a group of private and public organizations whose goal is to develop a wider understanding within Congress of the value of reducing the risks and costs of natural disasters. Information on the Natural Hazards Caucus Work Group can be found at: http://www.agiweb.org/gap/workgroup/resources.html. Some of the lead organizations include the American Meteorological Society and University Corporation for Atmospheric Research (http://www2.ucar.edu/), and the National Science Foundation (http//www.nsf.gov). Federal Emergency Management Agency (FEMA) 500 C Street, SW Washington, D.C. 20472 202-646-4600 http://www.fema.gov FEMA is the nation’s premier agency that deals with emergency management and preparation, and issues warnings and evacuation orders when disasters appear imminent. FEMA maintains a web site that is updated at least daily and includes information on hurricanes, floods, fires, national flood insurance, and information on disaster prevention, preparation, and emergency management. Divided into national and regional sites. Also contains information on costs of disasters, maps, and directions on how to do business with FEMA. U.S. Geological Survey U.S. Department of the Interior 345 Middlefield Road Menlo Park, CA 94025 650-329-5042 also, offices in Reston, VA, Denver, CO http://www.usgs.gov/ The USGS is responsible for making maps of many of the different types of hazards discussed in this book, including earthquake and volcano hazards, tsunami, floods, landslides, and radon. The National Landslide Information Center of the USGS is at: http://landslides.usgs.gov/nlic/ National Oceanographic and Atmospheric Administration (NOAA) http://www.noaa.gov/ NOAA conducts research and gathers data about the global oceans, atmosphere, space, and the sun and applies this knowledge to science and service that touch lives of all


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Americans. NOAA’s mission is to describe and predict changes in the Earth’s environment, and conserve and wisely manage the nation’s coastal and marine resources. NOAA’s strategy consists of seven interrelated strategic goals for environmental assessment, prediction, and stewardship. These include (1) advance short-term warnings and forecast services, (2) implement season to interannual climate forecasts, (3) assess and predict decadal to centennial change, (4) promote safe navigation, (5) build sustainable fisheries, (6) recover protected species, and (7) sustain healthy coastal ecosystems. NOAA runs a web site that includes links to current satellite images of weather hazards, issues warnings of current coastal hazards and disasters, and has an extensive historical and educational service. The National Hurricane Center http://www.nhc.noaa.gov/ is a branch of NOAA, and posts regular updates of hurricane paths and hazards.


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Chapter 11 Coastal Hazards Learning Objectives In this chapter we focus on one of the most dynamic environments on Earth—the coast, where the sea meets the land. Beaches composed of sand or pebbles and rocky coastlines continue to attract tourists and new residents like few other areas, yet most of us have little understanding of how ocean waves form and change coastlines. A major goal of this chapter is to remove the mystery of the processes at work in coastal areas while retaining the wonder. We also seek to explain the hazards resulting from waves, currents, and rising sea level, and how we can learn to live in the ever-changing coastal environment while sustaining its beauty. Your goals in reading this chapter will be to

• understand coastal processes such as waves, beach forms and processes, and rising sea level.

• understand coastal hazards such as rip currents and erosion. • know what geographic regions are at risk for coastal hazards. • understand the effects of coastal processes such as rip currents, coastal

erosion, and rising sea level. • recognize the linkages between coastal processes and other natural

hazards. • know the benefits derived from coastal processes. • understand how human use of the coastal zone affects coastal processes. • know what we can do to minimize coastal hazards. • understand the adjustments that can be made to avoid damage from coastal

erosion and rising sea level or personal injury from strong coastal currents. Chapter Outline 11. Coastal Hazards

11.1. Introduction to Coastal Hazards 11.2. Coastal Processes

11.2.1. Waves Case Study 11.1: Rogue Waves 11.2.1.1. Variations along a Coastline 11.2.1.2. Effects of Wave Refraction 11.2.1.3. Breaking Waves

11.2.2. Beach Form and Processes 11.2.2.1. The Beach Onshore 11.2.2.2. The Beach Offshore


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11.2.2.3. Sand Transport 11.3. Sea Level Change

11.3.1. Eustatic Sea Level 11.3.2. Relative Sea Level

11.4. Geographic Regions at Risk for Coastal Hazards 11.5. Effects of Coastal Processes

11.5.1. Rip Currents Survivor Story 11.2: Rip Current

11.5.2. Coastal Erosion 11.5.2.1. Beach Erosion

Professional Profile 11.3: Rob Thieler, Marine Geologist 11.5.2.2. Cliff Erosion

A Closer Look 11.4: Beach Budget 11.6. Linkages between Coastal Processes and Other Natural Hazards 11.7. Natural Service Functions of Coastal Processes 11.8. Human Interaction with Coastal Processes

11.8.1. The Atlantic Coast 11.8.2. The Gulf Coast 11.8.3. The Great Lakes 11.8.4. Canadian Seacoasts

11.9. Minimizing the Effects of Coastal Hazards 11.9.1. Hard Stabilization

11.9.1.1. Seawalls 11.9.1.2. Groins 11.9.1.3. Breakwaters and Jetties

11.9.2. Soft Stabilization 11.9.2.1. Beach Nourishment

11.10. Perception of and Adjustment to Coastal Hazards 11.10.1. Perception of Coastal Hazards 11.10.2. Adjustment to Coastal Hazards

A Closer Look 11.5: E-Lines and E-Zones Case Study 11.6: Moving the Cape Hatteras Lighthouse Case Study 11.7: Coastal Erosion at Pointe du Hoc, France

Chapter Summary Most waves are generated by windstorms at sea or on large lakes and expend their energy on the shoreline. The size of these waves in open water depends on a combination of wind speed, duration of the wind, and fetch. Waves approaching the shore are slowed by friction and can double in height. The height of waves grows larger in storms and wave energy is proportional to the square of this height. Irregularities in the shoreline focus wave energy and account for local differences in wave erosion; these irregularities are largely responsible for determining the shape of the coast.


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Beaches consist of sand or gravel deposited at the coast and may have other loose material, such as broken shells, coral, or volcanic rock, that was eroded locally. Beach sediment comes from erosion of cliffs, bluffs, or dunes landward of the beach, the shoreline updrift from the beach, or from rivers bringing sediment to the sea. Wave action by spilling or plunging waves shapes the beach. Most waves strike a beach at an angle, producing a longshore current parallel to the shore. This current, combined with beach drift, produces littoral transport of sediment parallel to the coast.

Coastal hazards include tidal currents, rip currents generated in the surf zone, coastal erosion, rogue waves, rising sea level, tsunamis, and cyclones. Tidal currents can be hazardous in narrow bays and channels, especially on the coasts with large tidal ranges. Beaches experiencing waves from storm swells or plunging breakers commonly have hazardous rip currents that can carry even the strongest swimmers offshore. Storm waves, enhanced by rising sea level and deficits in sand supply, contribute to coastal erosion. Hazardous rogue waves can form in the open ocean by the constructive interference of waves of similar size and wavelength.

Relative sea level, the place where the sea meets the land, is influenced by eustatic sea level and other local or regional changes in land or water position caused by tectonic uplift, coastal subsidence, erosion and deposition, and tides. Eustatic sea level is the global position of the ocean surface. Over decades this level is influenced by climate change. Today, rising eustatic sea level is being caused by global warming which expands ocean volume and melts glaciers, ice caps, and ice sheets. Tsunamis and cyclones can produce deadly surges of water flooding coastal areas. Storm surge, most commonly from hurricanes, is a function of the wind speed of the storm, atmospheric pressure, water depth, and the configuration of the coastline.

Rip currents occur on most seacoasts and sometimes in large lakes. Tidal currents are especially hazardous in areas with large tidal ranges, such as Alaska, the Pacific Northwest, and parts of New England and Atlantic Canada. Although coastal erosion causes a relatively small amount of damage compared to river flooding, earthquakes, and tropical cyclones, it is a serious problem along all the coasts of the United States, Great Lakes shorelines, and many Canadian seacoasts. Factors contributing to coastal erosion include river damming, high-magnitude storms, and the worldwide rise in sea level.

Human interference with natural coastal processes by hard stabilization of the shoreline is occasionally successful but in many cases causes considerable coastal erosion. Sand tends to accumulate on the updrift side of groins and jetties and then erode on the downdrift side. Seawalls reflect storm waves and cause beach erosion. Most problems with coastal erosion occur in areas with high population density, but sparsely populated areas along the Outer Banks in North Carolina are also experiencing trouble. Soft stabilization, such as beach nourishment, has had limited success in restoring or widening beaches, but even in “successful” cases it remains to be seen whether it will be effective in the long term.

Perception of coastal hazards depends mainly on the individual’s experience with and proximity to the hazard. Community adjustments in developed countries involve either building protective structures to lessen potential damage or modifying people’s behavior through land-use zoning, evacuation procedures, and warning systems.


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Adjustment to coastal erosion in developed areas has often been the “technological fix” of building seawalls, groins, and other structures and more recently, beach nourishment. These approaches to beach stabilization have had mixed success and often cause additional problems in adjacent areas. Engineering structures are very expensive, require maintenance, and once in place are difficult to remove. The cost of engineering structures may eventually exceed the value of the properties they protect; such structures may even destroy the beaches they were intended to save. Establishing setback distances and managed retreat can be effective adjustments to rising sea level. Answers to Review Questions: 1. How do waves on a lake or ocean form? What affects their height? (p. 369)

Waves form from off shore wind. The wind blowing across the surface causes friction thus transferring some energy to the water producing a wave. The size of waves on a lake or in the ocean depends on the velocity or speed of the wind, the duration of the wind, and the distance that the wind blows across the water surface.

2. How is wave height related to the energy of the wave? (p. 370) Wave energy is approximately proportional to the square of the wave height.

3. What conditions favor the development of large, wind-driven waves? (p. 369) Large, wind-driven waves are caused by long duration wind acting over a large area (fetch).

4. Describe how water particles behave as a wind-driven wave passes. How does this behavior change in shallow water? (p. 371)

Water particles behave like rotating circles or ovals. As they enter shallow water, these cells become smaller and more elliptical in shape.

5. Describe what happens to waves as they enter shallow water. (p. 371)

When waves enter shallow water, the orbits become elliptical and the particle paths at depth are slowed down by friction from the sea bottom, while the particles near the sea surface retain their original velocity. Thus, the wave becomes oversteepened and eventually breaks.

6. Explain wave convergence and divergence at a headland. (p. 372)


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To visualize the effects of wave refraction, draw a series of imaginary lines, called wave normals, perpendicular to the wave fronts and add arrows pointing toward the shoreline. Wave refraction causes convergence of the wave normals at the headland and a divergence of the wave normals along the shoreline away from the headland. Where the wave normals converge, wave height and the energy expended by the waves both increase. Thus, the largest waves along a shoreline are generally found at the end of a rocky headland. The long-term effect of greater energy expenditure at a headland and other protruding areas is that wave erosion tends to straighten the shoreline.

7. Describe how breakers form and how the two most common types occur and behave. (pp. 372–373)

Breakers form from storms and from friction along the base of the wave as the wave approaches the shore. Circular particle paths at depth become elliptical and are slowed down by friction from the sea bottom, while the particles near the sea surface retain their original velocity. Thus, the wave becomes oversteepened and eventually breaks when the top of the wave overtakes the deeper parts. The two most common types of breakers are plunging breakers and spilling breakers. Plunging breakers form on steep beaches and tend to be erosive, while spilling breakers tend to develop on wide beaches and deposit sand.

8. Explain how littoral transport takes place and how longshore drift is related to direction of wave approach. (pp. 374–375)

Littoral transport is sand movement parallel to the shoreline in the swash and surf zones. Long shore drift is related to direction of wave approach because the drift moves parallel to the shoreline.

9. What causes tides and strong tidal currents? (p. 375) Astronomical tides are produced by the gravitational pull of the moon and to a lesser extent the sun.

10. Explain the difference between eustatic and relative sea level, and the factors that control each. (pp. 375–376)

Eustatic sea level is controlled by processes that affect the overall volume of water in the ocean and shape of the ocean basins. Climate, primarily the average air temperature, is the dominant control on the amount of water in the ocean today through a process called thermal expansion. Changes in air temperature cause ice on land to melt or freeze, thus affecting the amount of


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water in the world’s oceans. Large-scale processes, such as the rate of seafloor spreading at mid-ocean ridges, also influence global sea level. Relative sea level is the position of the sea at the shore. Movement of the shoreline is influenced by the rates of deposition, erosion, or subsidence along the coast. Astronomical tides and weather conditions primarily control relative sea level.

11. What are the most serious hazards affecting the coasts? (p. 376) Strong nearshore currents, sea-level rise, storm surge from cyclones, and tsunamis are hazards on some coastlines, while coastal erosion is a universal hazard. Strong coastal currents caused by artificial structures and astronomical tides are especially dangerous.

12. Describe how you recognize rip currents, how they form, and what you should do if you are caught in one. (pp. 377–380)

Rip currents, powerful currents that carry large amounts of water away from shore, develop when a series of large waves pile up water between the longshore bar and the swash zone. The water does not return offshore the way it came in but instead is concentrated in narrow zones to form rip currents. Rip currents are relatively narrow, form in the surf zone, and extend out perpendicular to the shoreline. They are fed by longshore currents and make their own channel as they pass through the longshore bar, widening and dissipating once they have passed the line of breaking waves. Before venturing into the ocean, a swimmer should first watch the waves to note the pattern of the regularly arriving sets of small and larger waves. Rip currents can form quickly after the arrival of a set of large waves. They can be recognized as a relatively quiet area in the surf zone where fewer incoming waves break. Visually, the rip current may appear as a mass of water and debris moving out through the surf zone. The water in the current may also be a different color because it carries suspended sediment. To safely escape a rip current, a swimmer must first recognize the current and then swim parallel to the shore until he or she is outside the current. Only then should the swimmer attempt to swim back to the shore. If you can’t reach shore, wave an arm and yell for help. The key to survival is not to panic.

13. What are the primary causes of coastal erosion? Why is coastal erosion becoming more common and also more of a problem? (pp. 380–385)

Coastal processes, such as beach drift, longshore drift, and local wave erosion, are the primary causes of coastal erosion. The continuing global rise in sea


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level and extensive development in the coastal zone makes coastal erosion a more serious problem.

14. Describe the processes that cause erosion of sea cliffs and lakeshore bluffs. (p. 382)

Wave action and land erosion by running water and landslides, sometimes compounded by poor development decisions, can cause erosion of sea cliffs and lakeshore bluffs. Human activities that increase erosion include uncontrolled surface runoff, increased groundwater discharge, the addition of weight to the top of a cliff, and increased amounts of groundwater discharging from the base of the cliff.

15. How are coastal processes related to flooding, landslides, subsidence, and climate change? (p. 385)

Intense precipitation drives many coastal hazards, such as flooding, erosion, and landslides. Storm surge and heavy rainfall inland combine to cause widespread coastal flooding. Areas where the coast has subsided are more vulnerable to both freshwater flooding and storm surge. Landslides are caused when wave erosion at the base of sea cliffs and lakeside bluffs undercuts the slope. Climatic conditions, such as the interaction between surface winds and sea surface temperatures in the Pacific Ocean known as El Niño, can also cause coastal erosion.

16. Describe the natural service functions of coastal processes. (p. 386) The beauty of the coastal zone that results in part from wave action and erosion draws many tourists to coastal zones. Coastal erosion is the only significant input of sand for many beaches. Without erosion of dunes, cliffs, and bluffs inland from the beach, or the erosion of updrift beaches, there would be very little sand to form a beach. Beach processes such as longshore drift maintain sandy beaches on all coasts, included lakeshores. Disturbance of the coastal zone and coral reefs by storm waves renews these ecosystems and maintains their diversity of life. Finally, coastal processes provide recreational opportunities, such as swimming, surfing, sailing, and fishing.

17. Explain the purpose and effects of seawalls, groins, breakwaters, and jetties. (pp. 391–393)

Seawalls are structures built on land parallel to the coastline to help retard erosion and protect buildings from damage. Groins are linear structures placed perpendicular to the shore usually in groups. Each groin is designed to trap a portion of the sand from the longshore drift. Breakwaters and jetties are linear structures of riprap that protect limited stretches of shoreline from waves. Breakwaters are designed to intercept waves and provide a rotated area or


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harbor for mooring boats or ships. Jetties are built in pairs perpendicular to the shore at the mouth of a river to prevent it from being blocked from sediment.

18. List arguments for and against beach nourishment. (pp. 393–394) Beach nourishment is aesthetically pleasing way to postpone erosion. However it is very expensive, and disrupts the natural flow of sediments through the beach environment.

19. What affects peoples’ perception of coastal hazards? (p. 395) People’s perception of hazards depends on their distance to the hazard and their intelligence and education. In general, the closer people are to the coast the more they know about coastal hazards because they may have seen the coastal zone in times of storms and other hazards. Some people have hurricane parties when a hurricane warning is issued, and these people tend not to perceive the danger of storm surges and high winds very well, and there are many incidents of hurricane parties being crashed by 20 foot tidal surges, with deadly consequences.

20. What are the five general principles that should be accepted if we choose to live with rather than control coastal erosion? (p. 397)

The five principles are: (1) coastal erosion is a natural process rather than a natural hazard; (2) any shoreline construction causes change; (3) stabilization of the coastal zone through engineering structures protects property but not the beach itself; (4) engineering structures designed to protect a beach may eventually destroy it; and (5) once constructed shoreline engineering structures produce a costly trend in coastal development that is difficult, if not impossible, to reverse.

21. Describe the adjustments that people need to make in order to protect themselves

from strong ocean currents and reduce coastal erosion. (p. 395)

Warning systems need to be put in place. Building designs should be modified to be more resistant to the hazards, and buildings should be located back away from the beach, out of the zone of mobile sand and dunes.

Answers to Critical Thinking Questions: 1. Do you think that human activity has increased coastal erosion? Outline a research

program that could test this question.


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Humans have increased coastal erosion. Study a beach without people living near it and a beach with people living on it and track the differences. Also, look at a beach that has recently been developed, and compare a series of old aerial photographs with new ones to track the rate of beach erosion before and after development.

2. Do you agree or disagree with the following statements: (1) All structures in the coastal zone, with the exception of critical facilities, should be considered temporary and expendable. (2) Any development in the coastal zone should be in the best interest of the general public rather than the few who developed the oceanfront. Explain your position on both statements.

All structures in the coastal zone are temporary, including critical facilities. Eventually the ocean will win. In general the public should have access to the coastal zone, though there is no defensible reason to stop those who can afford it to build and own their own ocean front property. However, these people should not rely on insurance to protect their property, where the general public will end up paying the cost of destroyed property. These properties should be self-insured.

3. You have been asked by a coastal community to evaluate the feasibility of a beach nourishment project. Describe the types of information that you would require for your evaluation and how you would determine how often nourishment will be needed in the future.

The types of waves and angles that they arrive at would need to be known, to determine the longshore drift, and the characteristic seasonal changes in onshore and offshore transport of sand. The topographic slope of the seafloor would need to be known, and the location of offshore bars, to know where the sand would come from.

4. Compare and contrast the shoreline features of tectonically active and passive coasts

of the United States, and describe how coastal hazards differ in the two coasts that you have evaluated.

Tectonically active shorelines such as the west coast (including the part of the coast where there is no longer subduction rather the San Andreas fault) are still undergoing isostatic adjustment and are characterized by an emerging coastline with lots of cliffs and steep coastline features. Cliff failure due to under cutting is a dominant hazard on the west coast. Compared to tectonically passive coastlines such as the east coast and gulf coast which are mostly drowned coasts with submerging coastlines are characterized by gradually sloping low lying coastlines with landward moving barrier islands produced by a submerging coastline. Thus, rising sea level will have the greatest effect on low coastlines. As sea level rises, the shoreline will shift the farthest distance inland


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on low coastlines causing damage to structures built too close to sea level even though these structures may be miles inland.

Suggested Activities 1. Go to the beach and watch how quickly the sand moves in the swash and backwash

zone by placing a marker (a bottle, dye, etc.) in this zone, and tracking the movement for an hour. Discuss the implications in terms of building on beaches, and stopping littoral drift with groins, and so forth.

2. Track damage from hurricanes, and discuss how the damage should be insured, and

what is likely to happen as storms increase in frequency and intensity with global warming.

Additional Resources (media, films, articles, journals, web sites) Print Resources Dealing with Coastal Hazards Bernard, E.N., (ed.), 1991, Tsunami Hazard: A Practical Guide for Tsunami Hazard

Reduction, Dordrecht, The Netherlands, Kluwer Academic Publishers. Booth, J.S., O’Leary, D.W., Popencoe, P., and Danforth, W.W., 1993, U.S. Atlantic

continental slope landslides: Their distribution, general attributes, and implications, U.S. Geological Survey Bulletin, v. 2002, 14–22.

Dawson, A.G., and Shi, S., 2000, Tsunami deposits, Pure and Applied Geophysics, v. 157, 493–511.

Dean, C., 1999, Against the Tide, The Battle for America’s Beaches, New York, Columbia University Press, 279 pp.

Dolan, R., Godfrey, P.J., and Odum, W.E., 1973, Man’s impact on the barrier islands of North Carolina, American Scientist, v. 61, 152–162.

Driscoll, N.W., Weissel, J.K., and Goff, J.A., 2000, Potential for large-scale submarine slope failure and tsunami generation along the U.S. mid-Atlantic coast, Geology, v. 28, 407–410.

Dvorak, J., and Peek, T., 1993, Swept away, Earth, v. 2 no. 4, 52–59. Federal Emergency Management Agency, 1986, Coastal Construction Manual, 104 pp. Horton, T., 1993, Hanging in the balance—Chesapeake Bay, National Geographic, v.

183 no. 6, 2–35. Kaufman, W., and Pilkey, O.H. Jr., 1983, The Beaches are Moving, Durham N.C., Duke

Univ. Press.


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King, C.A.M., 1961, Beaches and Coasts, London, Edward Arnold Publishers, 403 pp. Komar, P.D. (ed.), 1983, CRC Handbook of Coastal Processes and Erosion, Boca Raton,

Florida, CRC Press, pp. 123–150. Kusky, T.M., 2007, The Coast, Facts on File, Hazardous Earth Set. Latter, J.H., 1981, Tsunami of volcanic origin, summary of causes, with particular

reference to Krakatau, 1883, Journal of Volcanology, v. 44, 467–490. McCoy, F., and Heiken, G., 2000, Tsunami generated by the Late Bronze age eruption of

Thera (Santorini), Greece, Pure and Applied Geophysics, v. 157, 1227–1256. Miele, P. T., 2001, Air force plans for Fourth Cliff ride wave of worries over erosion,

Boston Globe, South Weekly, July 29, 1. Minoura, K., Imamura, F., Takahashi, T., and Shuto, N., 1997, Sequence of

sedimentation processes caused by the 1992 Flores tsunami, Evidence from Babi Island, Geology, v. 25, 523–526.

Minoura, K., Inamura, F., Nakamura, T., Papadopoulos, A., Takahashi, T., and Yalciner, A., 2000, Discovery of Minoan tsunami deposits, Geology, v. 28, 59–62.

Okazaki, S., Shibata, K., and Shuto, N., 1995, A road management approach for tsunami disaster planning, in Tsuchiya, Y., and Shuto, N. (eds.), Tsunami: Progress in Prediction Disaster Prevention and Warning, Boston, Kluwer Academic Publishers, pp. 223–234.

Revkin, A.C., 2000, Tidal waves called threat to East Coast, The New York Times, July 14, A18.

Satake, K., 1992, Tsunamis, Encyclopedia of Earth System Science, v. 4, pp. 389–397. Steinbrugge, K.V., 1982, Earthquakes, Volcanoes, and Tsunamis, An Anatomy of

Hazards, New York, Skandia America Group. Tsuchiya, Y., and Shuto, N. (eds.), 1995. Tsunami: Progress in Prediction Disaster

Prevention and Warning, Boston, Kluwer Academic Publishers, 336 pp. U.S.G.S., 1987, Surviving a tsunami-kesson from Chile, Hawaii, and Japan, U.S.

Geological Survey Circular 1187. Williams, S.J., Dodd, K., and Gohn, K.K., 1990, Coasts in crisis, U.S. Geological Survey

Circular 1075, 32 pp. Yeh, H., Imamura, F., Syndakis, C., Tsuji, Y., Liu, P., and Shi, S., 1993, The Flores

Island tsunami, EOS, Transactions of the American Geophysical Union, 73, N33. Nonprint Resources Dealing with Coastal Hazards Videos: The Beach: A River of Sand, 1996, Encyclopedia Britannica (21 mins). The Beaches are Moving: The Drowning of America’s Shoreline, 1990, Environmental

Media, (55 mins.). Web sites:


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National Oceanographic and Atmospheric Administration web site about hazards, including tsunamis: http://www.ngdc.noaa.gov/hazard/hazards.shtml Web site about tsunami research at the U.S. Geological Survey: http://walrus.wr.usgs.gov/tsunami Web site of the tsunami research Program at NOAA: http://nctr.pmel.noaa.gov/ Organizations Dealing with Coastal Disasters: Federal Emergency Management Agency (FEMA) 500 C Street SW Washington, D.C. 20472 Phone 202-646-4600 http://www.fema.gov FEMA is the nation’s premier agency that deals with emergency management and preparation, and issues warnings and evacuation orders when coastal storms and disasters appear imminent. FEMA maintains a web site that is updated at least daily, includes information of hurricanes, floods, fires, national flood insurance, and information on disaster prevention, preparation, emergency management. Divided into national and regional sites. Also contains information on costs of disasters, maps, and directions on how to do business with FEMA. National Tsunami Hazard Mitigation Program: this is a partnership between the states of Hawaii, Alaska, California, Oregon, and Washington, and the Federal Emergency Management Agency, National Oceanic and Atmospheric Administration, and the U.S. Geological Survey. This program is preparing maps showing tsunami inundation areas, and implementing mitigation plans for the states in the program. The NTHMP is also developing an early warning system, including seismic stations and deep ocean tsunami detectors. http://nctr.pmel.noaa.gov/ NOAA/Pacific Marine Environmental Laboratory, 7600 Sand Point Way N.E. Seattle, WA, 98115, USA, phone: 206-526-6800, fax: 206-526-6815 U.S. Geological Survey 345 Middlefield Road Menlo Park, CA 94025 650-329-5042 U.S. Geological Survey U.S. Department of the Interior USGS National Center 12201 Sunrise Valley Drive


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Reston, VA 20192, USA 703-648-4000 http://www.usgs.gov/ The main goal of the USGS is to provide scientific information on the biology, geography, geology, and hydrology of the Earth in order to protect and better our quality of life. The USGS is responsible for making maps of the coastal zone, and assessing risks along these zones. The USGS tracks all earthquakes, floods, and volcanic activity in the U.S. and is responsible for the storage of this data. US Army Corps of Engineers 441 G. Street, NW Washington, D.C. 20314 phone: 202-761-0008; fax: 202-761-1683 http://www.usace.army.mil/Pages/default.aspx http://www.usace.army.mil/Emergency/Pages/home.aspx The U.S. Army Corps of Engineers has an emergency response unit, set for responding to environmental, coastal, and other disasters. The Headquarters Office is a good place to start a search for any specific problem. National Oceanographic and Atmospheric Administration (NOAA) Department of Commerce 14th Street & Constitution Avenue, NW Room 6013 Washington, D.C. 20230 phone: 202-482-6090, fax: 202-482-3154 http://www.noaa.gov/ NOAA conducts research and gathers data about the global oceans, atmosphere, space and sun, and applies this knowledge to science and service that touch lives of all Americans. NOAA’s mission is to describe and predict changes in the Earth’s environment, and conserve and wisely manage the nation’s coastal and marine resources. NOAA’s strategy consists of seven interrelated strategic goals for environmental assessment, prediction, and stewardship. These include (1) advance short-term warnings and forecast services, (2) implement season to interannual climate forecasts, (3) assess and predict decadal to centennial change, (4) promote safe navigation, (5) build sustainable fisheries, (6) recover protected species, and (7) sustain healthy coastal ecosystems. NOAA runs a web site that includes links to current satellite images of weather hazards, issues warnings of current coastal hazards and disasters, and has an extensive historical and educational service.


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Chapter 12 Climate and Climate Change Learning Objectives Many natural hazards, such as drought, heat waves, floods, hurricanes, blizzards, and wildfire, are related to climate. Climate change is also a potential cause of extinction of plants and animals. A basic understanding of climate science is needed to comprehend the mechanisms of these hazards. Your goals in reading this chapter are to

• understand the difference between climate and weather, and how their variability is related to natural hazards.

• know the basic concepts of atmospheric science such as structure, composition, and dynamics of the atmosphere.

• understand how climate has changed during the past million years, through glacial and interglacial conditions, and how human activity is altering our current climate.

• understand the potential causes of climate change. • know how climate change is related to natural hazards. • know the ways we may mitigate climate change and associated hazards.

Chapter Outline 12. Climate and Climate Change

12.1. Global Change and Earth System Science: An Overview 12.2. Climate and Weather

12.2.1. Climate Zones 12.2.2. Earth Climate System and Natural Processes

12.3. The Atmosphere 12.3.1. Atmospheric Composition 12.3.2. Permanent and Variable Gases 12.3.3. Glaciations

12.3.3.1. Glacial Hazards 12.4. How We Study Past Climate Change and Make Predictions

12.4.1. Global Climate Models 12.5. Global Warming

12.5.1. The Greenhouse Effect 12.5.2. Global Temperature Change 12.5.3. Why Does Climate Change?

12.5.3.1. Climate Forcing


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12.5.4. Solar Forcing 12.5.5. Volcanic Forcing 12.5.6. Anthropogenic Forcing

12.6. Potential Effects of Global Climate Change 12.6.1. Glaciers and Sea Ice 12.6.2. Climate Patterns

A Closer Look 12.1: El Niño 12.6.3. Sea-Level Rise 12.6.4. Wildfires

Survivor Story 12.2: Residents of the Maldive Islands 12.6.5. Changes in the Biosphere 12.6.6. Adaptation of Species to Global Warming

A Closer Look 12.3: Marine Ecosystems and Climate Change 12.7. Predicting the Future Climate 12.8. Strategies for Reducing the Impact of Global Warming

A Closer Look 12.4: Abrupt Climate Change Professional Profile 12.5: Sally Benson – Climate and Energy Scientist

Chapter Summary The main goal of the emerging integrated field of study known as Earth system science is to obtain a basic understanding of how our planet works and how its various components, such as the atmosphere, oceans, and solid Earth, interact. Another important goal is to predict global changes that are likely to occur within the next several decades. The global changes involved include temperature, or climate, changes and the resulting changes in seawater and on land. Because these are short-term predictions, Earth system science is relevant to people everywhere.

Methods of studying global change include examination of the geologic record from lake sediments, glacial ice, and other Earth materials; gathering of real-time data from monitoring stations; and development of mathematical models to predict change.

Climate refers to characteristic atmospheric conditions, such as precipitation and temperature over seasons, years, and decades. The atmosphere is a dynamic, complex environment in which many important chemical reactions occur.

Human activity is contributing significantly to global warming. The trapping of heat by the atmosphere is generally referred to as the greenhouse effect. Water vapor and several other gases, including carbon dioxide, methane, and chlorofluorocarbons, tend to trap heat and warm Earth because they absorb some of the heat energy radiating from Earth. The effects of a global rise in temperature include a rise in global sea level and changes in rainfall patterns, high-magnitude storms, soil moisture, agriculture, and the biosphere.

Natural climate-forcing mechanisms that may cause climatic change include Milankovitch cycles, solar variability, and volcanic activity. Anthropogenic causes


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include air pollution and increase in greenhouse gases, especially carbon dioxide. We now understand that global climate can change rapidly over a time period of a few decades to a few hundred years. Two important questions are (1) What is the nature and extent of past climate change? and (2) What climate changes will occur in the future?

The science of global warming is well understood. Human-induced global warming is occurring. There is no reason for gloom and doom, but we need to take appropriate action soon to slow or stop global warming and associated environmental consequences.

Adjustments to global warming will range from adapting to change to reducing emissions of carbon dioxide and sequestration of carbon. Several different, simultaneous adjustments are likely. Answers to Review Questions: 1. What is the distinction between climate and weather? (p. 409)

Climate refers to the characteristic atmospheric conditions at a given location over long periods of time, whereas weather refers to conditions over short periods of time such as days or weeks.

2. What is the basis for climate classification? (p. 409)

The basis is temperature and precipitation.

3. List the different forms of water in the atmosphere.

(Note: This question was changed from previous edition and does NOT have a defined answer in this chapter. This information was moved to Chapter 9.)

4. What is climate proxy data and why is it important? (p. 414)

Climate proxy data refers to data that is not strictly climatic but can be correlated with climate, such as temperature of the land or sea. Paleoclimate proxy data preserved in the geologic record provide the best evidence of change that predates the historical and instrumental records.

5. How do aerosols influence climate? Where do they come from? (pp. 409–411)

Aerosols are colloidal particles that are dispersed in gas, smoke, and fog, and are important in cloud formation. They act as the nuclei around which water droplets condense to form clouds. Their presence can lead to either cooling or warming of the air.

6. Explain or diagram the general global pattern of atmospheric circulation.


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(Note: Although Atmospheric circulation is referenced in this chapter three times, it is NOT defined or explained. This information was moved to Chapter 9.)

7. What is an interglacial? (p. 411)

An interglacial is a period of less glaciation to no glaciation, when the glaciers have retreated back toward the poles.

8. What are the potential causes of continental glaciation?

(Note: The information required to answer this question is no longer contained in this book. The in-depth discussion was deleted from this edition.) The causes of major global glacial events are unknown, but they appear to be related to the position of the continents, which significantly affects both ocean circulation and global climate. Once a glacial event has begun, changes in the amount of solar radiation reaching Earth’s surface influence the advances and retreats of continental glaciers. These changes are influenced by astronomical or orbital cycles known as Milankovitch cycles in which the Earth’s orbit around the sun and the tilt and wobble of the Earth’s axis or rotation change.

9. How can glaciers be hazardous? (pp. 412–413)

Glaciers are huge, actively flowing masses of ice and rock debris whose movement and melting have been responsible for property damage, injuries, and deaths. Their irregular surface, including crevasses, provides hazards to those exploring over the terrain. One of the biggest hazards of glaciers is when icebergs calve off of glaciers or ice shelves and enter shipping lanes, forming a hazard to shipping.

10. What is climate forcing and how does it work? (p. 423)

Climate forcing is defined as an imposed change of Earth’s energy balance. The units for the forcing are and they can be positive if a particular forcing increases global mean temperature or negative if temperature is decreased. For example, if the energy from the sun increases, then Earth will warm (this is positive climate forcing).

11. Explain or diagram the greenhouse effect. Describe the types of radiation that are

involved and the wavelength of the radiation. (pp. 419–421) The greenhouse effect is caused by several gases that trap energy in the form of heat in the atmosphere. Energy enters the atmosphere in short wavelengths that can penetrate the clouds and gases in the atmosphere. However, when this radiation is re-reflected from the Earth it is reflected at longer wavelengths that cannot penetrate the clouds and atmospheric gases, so it remains in the


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atmosphere as heat energy. Carbon dioxide, nitrogen dioxide, nitrogen oxides, and chlorofluorocarbons absorb the infrared radiation and increase the air temperature.

12. List the major greenhouse gases and their natural and anthropogenic sources. Which

gases are enhancing the greenhouse effect the most? (pp. 420–423)

Carbon dioxide, methane, nitrous oxide, and halocarbons are referred to as greenhouse gases. Carbon dioxide accounts for around 56 percent of the anthropogenic greenhouse effect. Carbon dioxide is released into the atmosphere naturally through volcanic activity, plant and animal respiration, and decay of organic material. Human sources have primarily been the burning of fossil fuels and cement production, and indirectly through deforestation, because fewer trees are available to remove carbon dioxide from the air. Methane occurs naturally from bacterial decay in moist places that lack oxygen, such as marshes and swamps. Anthropogenic sources of methane include coal mines, oil wells, leaking natural gas pipelines, rive cultivation, landfills, and livestock. Natural sources of nitrous oxide include microbiological processes in the soil and ocean and wildfires. Anthropogenic sources include fertilizer use and burning fossil fuels. Halocarbons are entirely anthropogenic. They are used in industrial processes, firefighting, and as fumigants, refrigerants, and propellants.

13. What is the Milankovitch effect? What are the three changes in the Earth’s orbit that

cause this effect? (p. 421) The Milankovitch effect is a theory of climate change that accounts for the orbit, tilt, and wobble of the Earth relative to its rotation around the sun. Cyclical changes in these orbital parameters, with different time periods, cause systematic variations in the amount of incoming solar radiation, and thus causes changes in climate. The different periodicities of each orbital parameter cause a complex pattern of cycles with different strengths and periods.

14. Explain solar, volcanic, and anthropogenic forcing. (pp. 426–427)

Solar forcing is the evaluation of the change of intensity of the sun as a reason for possible climate change. Volcanic forcing is the evaluation of the change in global temperature based on volcanic particles floating through the air—eruptions can change the temperature of the Earth for years by a few degrees.


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Anthropogenic forcing is the evaluation of how humans have changed the temperature of the Earth.

15. Describe the natural hazards associated with climate change. (Generally discussed

throughout the chapter) Hazards associated with global warming include climate change, rising sea level, intensification of storms, shifting of climate and agricultural zones, changes in the biosphere, and desertification and drought.

16. How is climate change likely to affect the weather? (Generally discussed throughout

the chapter)

Weather patterns shift as climate changes. Changing climate patterns will alter the location of agricultural zones, and affect weather patterns; melting glaciers and ice sheets will contribute to the continuing rise in global sea level, and species may lose some of their habitat; and global temperature increases may lead to desertification of arid lands, droughts, and an increase in frequency and intensity of wildfires.

17. Which processes are contributing the most to rising sea level? (p. 433)

The primary cause of current sea level rise is the thermal expansion of water due to the temperature increase from global warming. The secondary cause is icecaps melting.

18. How will climate change affect the biosphere? (p. 435)

Changes in the biosphere include shifts in the range of plants and animals as well as changes in the habitat where a plant or animal lives. Warmer water temperatures and ocean acidification threatens coral, shellfish, and other reef invertebrates.

19. How is drought related to global warming? (p. 433)

Climate change will likely exacerbate the phenomenon known as desertification—the conversion of land to land resembling desert—in areas that are already becoming warmer and drier. An increase in drought events will result from global warming, thus putting pressure on food and water supplies. If climate zones shift, it is likely that areas with no significant history of droughts will have to cope with them.

20. Which parts of our planet are experiencing the greatest effects of climate change? (p. 428)


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These areas include coastlines with elevations close to sea level and areas which are already experiencing frequent drought, such as the Sahel of Africa.

21. What are the projected changes to our climate for the remainder of this century? (p.

438) Two possible scenarios exist for global warming and sea-level rise during the next 100 years. In the first scenario, more efficient technologies are introduced, but the energy system remains fossil-fuel intensive. The average global temperature is predicted to rise around 4.5˚ (8˚F) and sea level may rise as much as 1.4 m (4.6 ft.). In the second scenario, economic structures have changed, reducing material intensity and introducing clean resource-efficient technologies. In this scenario, average global temperature is predicted to rise only about 2˚C (3.6˚F), and sea level rise will be under 0.5 m (2 ft.).

22. How have international agreements dealt with ozone depletion and climate changes? (Note: this question is no longer discussed to any great extent in this edition, especially as it pertains to ozone.) International agreements have attempted to capture and store carbon dioxide, but have been hampered by lack of cooperation.

23. What are the proposed methods for carbon sequestration? What methods hold the

greatest promise and why? (pp. 438–439) Of the three major options for sequestration, biological, oceanic, and geologic, the geologic option is the most promising. Biological sequestration, such as by planting more trees, is a much slower process and pales in comparison to the amount of carbon dioxide that must be removed from the atmosphere. Fertilizing ocean plankton with iron is limited in its capacity to remove carbon dioxide and has unknown side effects in the marine environment. Injecting carbon dioxide in the oceans would further acidify the ocean and potentially wreak havoc on marine ecosystems. Geologic sequestration holds the most promise because the residence time of carbon in the geologic environment is potentially thousands to hundreds of thousands of years.

24. Explain El Niño and its effects. (pp. 430–433)

El Niño may start with a slight reduction in trade winds, which causes warm water in the western equatorial Pacific Ocean to flow eastward. This eastward flow further reduces the trade winds, causing more warm water to move eastward until an El Niño event is established. The El Niño brings heavy rains to northern South America and Central America, and the warm surface waters disrupt the normal coastal upwelling of nutrient-rich cold deep water, destroying the fish population and all that rely on it (birds, people, etc.). El


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Niño is associated with storms and landslides in these regions, although its effects are felt globally.

25. What changes should individuals, the private sector, and government make to reduce greenhouse gases? (pp. 437–441)

Regulatory, technological, and behavioral changes will have to be made at individual, community, national, and international levels. The best solutions include a reduction of our dependency on fossil fuels and a switch to clean-energy alternatives.

Answers to Critical Thinking Questions: 1. In this chapter we discussed some possible effects of continued global warming. What

types of hazards would you expect to increase in your area as the climate changes? Would you expect to see any decrease? Think about the ways climate change might alter the life and lifestyles of people living in your area. Do you see any evidence of climate change where you live?

I would expect more flooding. People would have to get used to more extreme weather and so state programs would need to become faster and better at responding to such incidences. Warming might also change the ability of corn and soybeans to grow in central U.S., displacing these crops to more northern zones such as southern Canada.

2. Assessing the rate and cause of change is important in many disciplines. Have a

discussion with a parent or someone of similar age and write down the major changes that have occurred in his or her lifetime and in your lifetime. Characterize these changes as gradual, abrupt, surprising, chaotic, or another descriptive word of your choice. Analyze these changes and discuss which ones were most important to you personally. Which of these changes affected your environment at the local, regional, or global level?

The ones most important were flooding and tornados. Flooding will affect my environment at a local, regional, and global level.

3. How do you think climate change is likely to affect you in the future? What

adjustments will you have to make? What can you do to mitigate the effects?

Global warming will increase the severity of weather like droughts and thunderstorms and hurricanes. We will have to learn how to preserve water during dry seasons and collect it during rainy seasons.


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4. Some people, for cultural, political, religious, or other reasons, do not accept the

conclusions that climate change is taking place and that it is primarily caused by human activities. What do you see as the basis for their opinions or beliefs? How do you think they might be convinced otherwise? If you share their opinions or beliefs, indicate why you do and what it would take to convince you that climate change is the result of human activities.

I think that they are relying on old data and that they are scared to admit that what they are doing now already may be affecting humanity. The data that humans are causing an increase in temperature of somewhat less than 1 degree is pretty clear, but even so this data needs to be looked at in a longer time context. The Earth has gone through many ice house and hot house events before humans were here, and our little blip on the global climate fluctuations on these scales may not be as significant as many believe. Even so, the changes induced by humans are real, and the effects will need to be dealt with by our and future generations.

Suggested Activities 1. Discuss what rising sea levels will mean for coastal cities such as New York, Miami,

Los Angeles, London, Hong Kong, Shanghai, Sydney, etc. 2. Divide the class into two groups, the environmentalists and the industrialists, and

have them debate the merits of cutting greenhouse emissions vs. the increasing cost of products to consumers.

Additional Resources (media, films, articles, journals, web sites) Print Resources Dealing with Global Climate Change Abrahams, A.D., and Parsons, A.J., 1994, Geomorphology of Desert Environments,

Chapman and Hall, 674 pp. Al-Dabi, H., 1996, Detection of Anthropogenic Changes in a Sand Dune Field of

Northeastern Kuwait Using Remotely Sensed Imagery, M.A. Thesis, Boston University, 75 pp.

Alley, R.B., and Bender, M.L., 1998, Greenland ice cores: Frozen in time, Scientific American, February.

Anderson, E., 1992, Water Conflict in the Middle East—A New Initiative, Janes Intelligence Review, v. 4, no. 5, 227–230.


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Bagnold, R.A., 1941, The Physics of Blown Sand and Desert Dunes, London, Methuen, 65 pp.

Blackwell, Major James, 1991, Thunder in the Desert, The Strategy and Tactics of the Persian Gulf War, Bantam, 252 pp.

Bryson, R., and Murray, T., 1977, Climates of Hunger, Canberra, Australian National University Press.

Dawson, A.G., 1992, Ice Age Earth, London, Routledge, 293 pp. Douglas, B., Kearney, M., and Leatherman, S., 2000, Sea Level Rise: History and

Consequences, International Geophysics Series, vol. 75, San Diego, Academic Press, 232 pp.

El-Baz, F., and Himida, I., 1996, Sand accumulations and groundwater in the Sahara, UNESCO, International Geological Correlation’s Program Project 391, Cairo, Egypt, Desert Research Center, 31 pp.

El-Baz, F., Kusky, T.M., Himida, I. and Abdel-Mogheeth, S., editors, 1998, Groundwater Potential of the Sinai Peninsula, Egypt, Cairo, Egypt, Desert Research Center, 219 pp.

El-Baz, F., and Sarawi, M. (editors) (12 coauthors, including T. Kusky), 2000, Atlas of the State of Kuwait from Satellite Images, Kuwait Foundation for the Advancement of Science, 145 large-format pages, printed in Germany by Cantz, ISBN 99906-30-00-3.

Erickson, J., 1996, Glacial Geology: How Ice Shapes the Land, Facts on File, Changing Earth Series.

Freidman, N., 1991, Desert Victory, The War for Kuwait, Naval Institute Press, 435 pp. Kusky, T.M., and El Baz, F., 1999, Structural and tectonic evolution of the Sinai

Peninsula, using Landsat data: implications for groundwater exploration, Egyptian Journal of Remote Sensing, v. 1, 69–100.

Kusky, T.M., 2007, Climate Change, Drought, and Glaciers, Facts on File, Hazardous Earth Set.

McKee, E.D., (editor), 1979, A study of global sand seas, U.S. Geological Survey Professional Paper 1052.

Molina, B., 1994, Modern surge of glacier comes to an end, Eos, Transactions of the American Geophysical Union, Nov. 22.

Reisner, M., 1986, Cadillac Desert, The American West and Its Disappearing Water, Penguin, 582 pp.

Schneider, D., 1997, The rising seas, Scientific American, March. Sorkhabi, R., 1993, Water for Peace or Wars Over Water: Hydropolitics in the Middle

East, The Professional Geologist, v. 30, no. 13, 8–9. Starr, J.R., 1991, Water Wars, Foreign Affairs, Spring 1991, no. 82. Starr, J.R., and Stoll, D.C., (eds.), 1988, The Politics of Scarcity, Water in the Middle

East, Westview Press, Boulder. Stone, G., 2001, Exploring Antarctica’s islands of ice, Dec. 2001, National Geographic,

36–51. Thomas, R., 2001, Remote sensing reveals shrinking Greenland Ice Sheet, EOS,

Transactions of the American Geophysical Union, v. 82, no. 34, 369–73. Walker, A.S., 1996, Deserts: Geology and Resources, U.S. Geological Survey,

Publication 421-577, 60 pp. Webster, D., 2002, Alashan, China’s unknown Gobi, National Geographic, 48–75.


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Nonprint Resources Dealing with Global Climate Change Videos: Emecorp, 1989, Glaciers, 15 mins. Award-winning photography shows glacial erosion in action! Advancing ice masses carve U-shaped valleys and leave a trail of lakes and erratics, while melting glaciers deposit kames, drumlins, and outwash plains. Covers alpine and continental glaciation. Animation sequences help explain key processes. Public Broadcasting System, 1985, Glaciers, Earth Explored Series, 28 mins. Web sites: http://bprc.osu.edu/polar_pointers/ This web site, called Polar Pointers, has many links to interesting sites about glaciers, glacial hazards, and arctic themes. http://earthobservatory.nasa.gov/IOTD/view.php?id=5668 This site, from NASA Goddard Space Flight Center's Scientific Visualization Studio, offers many extremely impressive views and animations of Greenland's receding glaciers. http://pubs.usgs.gov/gip/deserts/contents/ Web site that contains a huge amount of information about deserts, desert geology, hazards, and resources. The site is maintained by the United States Geological Survey, which is structured under the Department of the Interior. Includes descriptions of types of deserts and where exactly deserts form. Also discusses the use of remote sensing to map such deserts. http://www.earthobservatory.nasa.gov NASA’s Earth Observatory site about desertification and drought. Includes useful informational links to data and images, news, references, missions, and experiments. Contains stories on current desertification and drought on the Earth’s surface. http://www.aircav.com/survival/asch13/asch13p02.html Web site about how to survive in a desert. Includes precautionary measures and information on desert hazards. General information on related illnesses and what to do if you run out of water. Organizations Dealing with Global Climate Change http://www.dri.edu/ Desert Research Institute DRI is a part of the University of Nevada. The 400 members of the DRI staff are concerned with water resources and air quality, global climate change, and the physics of


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the Earth’s turbulent atmosphere, humanity’s historic struggle to adapt to harsh environments, and its urgent search today for the technology of the next century. http://cires.colorado.edu/parca.html NASA, National Aeronautics and Space Administration, Program for Arctic Regional Climate Assessment Researches the Greenland ice sheet by measuring changes in ice sheet volume, uses satellite and aircraft data to monitor glaciers, conducts field programs to measure in situ properties of glaciers. http://www.ngdc.noaa.gov/paleo/ NOAA Paleoclimatology Program At the National Geophysical Data Center, this is a central location for paleoclimate data, research, and education. Their mission, as stated on their web page, is to “help the World share scientific data and information related to climate system variability and predictability. Our mission is to ensure the international paleoclimate research community meets the scientific goals of programs including IPCC, IGBP PAGES, WCRP CLIVAR, and NOAA’s Climate and Global Change Program.” http://www.nsf.gov/dir/index.jsp?org=OPP National Science Foundation, Polar Research Program NSF states the mission of the Polar Research Program as follows: “The earth’s polar regions offer compelling scientific opportunities, but their isolation and their extreme climates challenge the achievement of these opportunities. The Foundation’s programs for support of research in the Antarctic and the Arctic acknowledge the need to understand the relationships of these regions with global processes and the need to understand the regions as unique entities. NSF’s polar programs, most of which are supported through the Office of Polar Programs, thus provide support for investigations in a range of scientific disciplines.”

http://acsys.npolar.no Arctic Climate System Study Mission The scientific goal of the Arctic Climate System Study(ACSYS) project is to ascertain the role of the Arctic in global climate by attempting to find answers to the following related questions: 1.What are the global consequences of natural or manmade change in the Arctic climate system? 2.Is the Arctic climate system as sensitive to increased greenhouse gases as climate models suggest?


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Chapter 13 Wildfires Learning Objectives As Earth’s population grows, more people are moving into and near brushlands, forest, and other wildlands where wildfires naturally occur. This trend increases the risk of property damage and loss of life from wildfires. Your goals in reading this chapter should be to

• understand wildfire as a natural process that becomes a hazard when people live in or near wildlands.

• understand the effects of fires. • know how wildfires are linked to other natural hazards. • know potential benefits provided by wildfire. • know the methods employed to minimize the fire hazard. • know the potential adjustments to the wildfire hazard.

Chapter Outline 13. Wildfires

13.1. Introduction to Wildfire 13.2. Wildfire as a Process

Case Study 13.1: Indonesian Fires of 1997–1998 13.2.1. Fire Environment

13.2.1.1. Fuel 13.2.1.2. Topography 13.2.1.3. Weather

13.2.2. Types of Fires 13.3. Geographic Regions at Risk from Wildfires 13.4. Effects of Wildfires and Linkages with Other Natural Hazards

13.4.1. Effects on the Geologic Environment 13.4.2. Effects on the Atmospheric Environment Case Study 13.2: Wildfire in Southern California

13.4.3. Linkages with Climate Change 13.4.4. Effects on the Biological Environment

13.4.4.1. Vegetation Professional Profile13.3: Wildfires

13.4.4.2. Animals 13.4.4.3. Human Beings

13.5. Natural Service Functions of Wildfires


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13.5.1. Benefits to Soil 13.5.2. Benefits to Plants and Animals 13.5.3. Yellowstone Fires of 1988

13.6. Minimizing the Wildfire Hazard 13.6.1. Fire Management

13.6.1.1. Science 13.6.1.2. Education 13.6.1.3. Data Collection 13.6.1.4. Prescribed Burns

13.7. Perception of and Adjustment to the Wildfire Hazard 13.7.1. Perception of the Wildfire Hazard 13.7.2. Adjustments to the Wildfire Hazard

13.7.2.1. Fire Danger Alerts and Warnings 13.7.2.2. Fire Education 13.7.2.3. Codes and Regulations 13.7.2.4. Fire Insurance 13.7.2.5. Evacuation

13.7.3. Personal Adjustment to the Fire Hazard Survivor Story 13.4: Two Wildfires in the Hills above Santa Barbara, California

Chapter Summary Wildfire, one of nature’s oldest natural processes, is a self-sustaining, rapid, high-temperature biochemical oxidation reaction that releases heat and light. Most wildfires in natural ecosystems maintain a rough balance between plant productivity and decomposition. For a fire to burn it must have fuel, oxygen, and heat. The two main processes that generate wildfire are preignition and combustion. Preignition involves heating a pyrolysis of fuel to drive off moisture and break down large carbon molecules into smaller ones. The smaller molecules create a cloud of flammable gas directly above the fuel, which then ignites. Ignition often starts with a lightning strike and then continues with windblown embers from the existing fire. Combustion typically occurs first by flaming, followed later by glowing and smoldering. Wildfires can be classified based on what part of the landscape burns. Surface fires are those that burn along the forest floor. Ground fires burn beneath the forest floor by smoldering. In forests, swamps, and marshes with organic soils, ground fires can smolder in peat deposits for many months. Fast-moving crown fires begin when surface fires ignite treetops. Spot fires are fires that are ignited ahead of the main fire by embers carried on the winds. Wildfire behavior is influenced by fuel, weather, topography, and the fire itself. Fuel varies in size, shape, arrangement, and moisture content and ranges from fast-burning grasses and conifer needles to slow-burning logs and soil organic matter.


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Weather conditions favoring wildfires include high winds and temperatures, low humidities, and dry thunderstorms. Longer-term drought conditions are especially favorable for wildfires. Fires spread rapidly up steep slopes and when spread by winds in canyons. Predictions of fire behavior rely on an understanding of the interaction between a fires environment and the fire regime. Fire can increase runoff, erosion, flooding, and landslides. Climate extremes, such as El Niño and La Niña, and global warming can increase wildfire activity in many regions. Natural service functions of fires includes increasing the nutrient content of soils, initiating regeneration of plant communities, creating new habitat for animals by altering landscapes, and potentially reducing the risk of large fires in the future.

Fire management includes education, data collection and mapping, and prescribed burns. Large wildfires are difficult to prevent and generally cannot be suppressed. Evacuation remains a primary adjustment for the wildfire hazard. Answers to Review Questions: 1. How has the nature of wildfires and human interaction changed over geologic and

historic time? (p. 448) Wildfires have become more dangerous to humans because humans are choosing and being forced by population density pressure to live in the wilderness or areas bordering on wilderness. This puts pressure on natural forest fires that are suppressed until they can be suppressed no longer, causing tragic wildfires. If fires were allowed to burn their natural course in the wilderness, the dead underbrush would be naturally thinned and natural processes would operate, but when small fires are put out to save homes the brush builds up until the fire potential becomes catastrophic.

2. How are wildfires related to plant photosynthesis and decomposition? (p. 448)

During a wildfire, plant tissue and other organic material is rapidly oxidized and broken down by combustion. Grass, brush, and forest lands burn because over long periods of time, these systems establish a balance between plant productivity and decomposition. Microbes alone do not decompose plants fast enough to balance plant grown, so wildfire helps in this decomposition. Fire, like the rotting or decomposition of dead plants by bacteria, essentially reverses the process of photosynthesis.

3. What are the major gases and solid particles produced by a wildfire? (pp. 448–450) The major gases produced by a wildfire are carbon monoxide and water vapor. Trace gases released are nitrogen oxide, carbonyl sulfide, carbon monoxide,


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methyl chloride, and hydrocarbons such as methane. The solid particles produced include ash and soot.

4. What are the three requirements for fire to start and for combustion to continue? What happens when one of these requirements is removed? (p. 450)

Fuel, oxygen, and heat are the three ingredients necessary to start a self-sustaining fire. If any of these three requirements are removed, the fire goes out.

5. What are the three phases of a wildfire? (p. 450)

The three phases of a wildfire are preignition, combustion, and extinction.

6. Explain how the two processes in the preignition phase prepare plant material for

combustion. (p. 450) The two phases are pre-heating and pyrolysis. During the pre-heating phase, the fuel loses a great deal of water and other volatile chemical compounds. Then during pyrolysis, heat divides, or splits, large fuel molecules into smaller ones. During this process, which operates continuously in a wildfire, the plant chemically degrades. Together, these processes produce the first fuel gases, which can ignite in the next phase of a fire called combustion.

7. What are the sources for the initial ignition of wildfires? How often does ignition occur in a wildfire? (p. 450)

Sources of initial ignition include lightning, volcanic activity, and human action, but many more ignitions occur than do wildfires. Ignition is not a single linear process; ignition repeats as a fire moves.

8. How do the processes of combustion differ from those of ignition? (p. 450) Ignition is the process of preparing the fuel. This is an energy gaining process. Combustion marks the start of a different set of processes. This process liberates energy in the form of heat and light.

9. What happens during pyrolysis? (p. 450)

Pyrolysis is a group of processes that chemically degrade the fuel as the heat splits large fuel molecules into smaller ones. The products include volatile gases, mineral ash, tars, and carbonaceous char.

10. Explain how the two types of combustion differ. (pp. 450–451)


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In flaming combustion, pyrolized (chemically broken down) wood burns hot and fast and releases great amounts of energy. After flaming combustion is complete, glowing or smoldering combustion takes over, and is characterized by wood that glows steadily as solid wood is consumed, releasing energy at a slower rate than in flaming combustion.

11. What are the three processes of heat transfer in a wildfire? Rank them in order of their importance. (p. 451)

The three primary ways by which heat is transferred, in order of importance, are convection, radiation, and conduction.

12. What three factors control the behaviors of a wildfire? (p. 451) The three factors that control the behaviors of a wildfire are fuel, topography, and weather.

13. How do topography and weather influence a wildfire? (pp. 452–453) The moisture content of fuel is influenced by its location on the landscape. For example, south-facing slopes in the Northern Hemisphere and the north-facing slopes in the Southern Hemisphere are relatively warmer and dryer than their counterparts. The lower moisture content favors combustion. Topography also influences air circulation. Slopes exposed to prevailing winds tend to have drier vegetation than slopes sheltered from the wind and thus are more prone to combustion. Mountainous areas, where winds tend to circulate up canyons during the daytime, provide an easy path for wildfires. Once a fire starts, topography can also strongly influence its movement. Steeper slopes have more preheat fuel upslope, increasing the rate of movement of the fire. Weather, particularly, temperature, precipitation, relative humidity, and winds, has a dominant influence on wildfire. Large wildfires are common following periods of drought when moisture content is reduced.

14. Describe the weather conditions that are most favorable for wildfires. (p. 453)

Favorable weather conditions include hot, dry conditions associated with drought; dry thunderstorms, in which rain evaporates before it reaches the ground and is not available to extinguish fires started by lightning; and low relative humidity. Winds also greatly influence the spread, intensity, and form of a wildfire.

15. Describe the three types of fire. (p. 453)


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There are three fire types—ground, surface, and crown. Ground fires creep along slowly just under the ground surface, with little flaming and more smoldering combustion. Surface fires, which move along the ground, may vary greatly in the amount of heat energy released by the fire. Low-intensity surface fires burn grass, shrubs, dead and downed limbs, leaf litter, and other debris. They burn relatively slowly with glowing or smoldering combustion and limited flaming combustion. Intense surface fires release large amounts of heat energy and move swiftly. Crown fires are those in which flaming combustion is carried through the canopies of the trees. Large crown fires are generally driven by strong winds and are often aided by steep slopes.

16. Explain how wildfires affect erosion of the land. (pp. 455–456)

Very hot fires occurring where the soil has a low moisture content may leave a water-repellent layer called a hydrophobic layer. This layer increases erosion and surface runoff because there is a lack of vegetation as well as loose soil above the layer. Landslides also increase on steep slopes after fires.

17. What effects do wildfires have on the atmosphere? (p. 456)

Wildfires significantly increase the level of particulates in the atmosphere.

18. How are some plants specially adapted to fire? (pp. 460–462)

Some plants, such as some species of pine, have come to depend on wildfires for propagation, as the heat of the fire releases seeds. Fires also help the decomposition of the above-surface portion of the plant, leaving the roots to grow anew.

19. Describe how climate change is likely to affect the frequency and intensity of

wildfires. (p. 460) Climate change is likely to increase both the intensity and frequency of wildfires. This increase may be brought about by changes in temperature, precipitation, and the frequency and intensity of severe storms. It may also be linked to biological changes that have taken place in the type and quantity of fuel available for wildfires.

20. Explain how wildfires in peatlands are especially hazardous. (p. 460)

Burning peat, an unconsolidated deposit of partially decayed wood, leaves, and moss, releases smog-producing gases, higher levels of particulates than the combustion of wood or grass, and significant quantities of toxic mercury into the environment.


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21. How do wildfires affect vegetation, animals, and humans? (pp. 460–463) Some plants are easily killed by fire, while other plants rely on fires for propagation. Most animals are able to escape wildfires. Although wildfire has few direct effects on wildlife, loss of groundcover in fire-denuded areas may lead to increased ground temperatures that alter habitats. Pioneering plant species in intensely burned areas will determine the type and number of vertebrates that can thrive there. Fish and other aquatic species may suffer from increased sedimentation, and water temperature may increase because plants along stream banks have been destroyed. Smoke and haze produced by fires can harm human health. Wildfire can destroy personal property and leave an area more susceptible to erosion, which may negatively affect water quality.

22. What are the natural service functions of wildfires? (pp. 463–464)

Wildfires remove the dead plants so that new growth may occur, facilitate some plant reproductive processes, such as aiding the release of seeds from some pine species, increase the nutrient content of soil, and destroy harmful microorganisms.

23. What are the four primary approaches to fire management? (p. 464)

The four primary approaches to fire management are education, scientific understanding, data collection to determine fire hazard potential, and prescribed burns in dangerous areas.

24. What are the difficulties associated with prescribed burns? (pp. 464–465)

The difficulties include calculation of fuel and predicting the weather under which they can control the fire safely. Planners must take into consideration the temperature, humidity, and wind, as well as microclimates.

25. Explain how people can adjust to the wildfire hazard. (pp. 465–467) Adjustment to the fire hazard may be accomplished through danger alerts and warnings, education, codes and regulation, insurance, and evacuation.


1. You live in an area with a significant wildfire hazard. What can you do to protect

your home and belongings from fires? Make a list of actions you can take to protect yourself.


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One could keep the vegetation moist near the house or remove it. It would also be smart to request a prescribed burn in dry areas a short distance from your house. Any sort of preventative and educational action is key.

2. The staff of a large national park is reviewing its fire policy. They have called upon

you, a wildfire expert, for advice. Their current policy is to suppress all fires as soon as they begin. They do not use controlled burns. They are considering switching to a policy of allowing natural burns. What would you suggest? List pros and cons of each policy before making your decision.

They should move to a policy of controlled burns. In this way they can attempt to control a fire before it gets out of hand due to excess fuel. The downsides are that it can be difficult to control a burn once it has been started.

3. Describe the features in and surrounding your home that might make it vulnerable to

a wildfire. Environmental features in and surrounding a home, making it vulnerable to a wildfire include: dead trees and a sunny plot of land in an area where wildfires typically occur but have not for several years. Fires may also occur because of a drought.

4. Most discussion of the wildfire hazard focuses on the potential destruction, injury, or death that can take place from the flames. Discuss the hazards to humans and the environment that come from the smoke produced by wildfires.

Wild fires have released enough smoke to blanket the area in smog (haze) which can cause health and economic problems throughout the region. Extreme levels of pollution and toxic substances, reduced visibility in some places which forced many residents to wear protective facemasks. In the most severely affected areas, many people developed chronic respiratory, eye, and skin ailments; schools and businesses were forced to close for days to weeks (such was the case in San Diego California during the October wildfires of 2007); and many premature deaths were blamed on the haze. Smoke/haze which reduces visibility can and has been known to contribute to aircraft crashes.



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1. Visit a local wooded area and see how much underbrush and other material may be available for fuel for a fire. Determine if any buildings are in danger from a fire in the area.

2. Visit the Internet sites that monitor wildfires, and see how many fires are burning

in places like Alaska, the western U.S., the Amazon, Australia, and Indonesia. Additional Resources (media, films, articles, journals, web sites) Print Resources Dealing with Wildfire Abbott, P.L., 2012, Natural Disasters, 8th ed., McGraw Hill, Boston, 512 pp. Bryant, E.A., 1993, Natural Hazards, Cambridge, Mass., Cambridge University Press,

294 pp. Eldredge, N., 1998, Life in the Balance, Princeton, N.J., Princeton University Press, 224

pp. Lyons, J.W., 1985, Fire, New York, Scientific American Books. Nonprint Resources Dealing with Wildfire Videos: Yellowstone Aflame, 1991, Finley-Holiday Film Corporation, 30 min. Wildfire, 1990, PBS video, 60 mins. http://www.wildlandfire.com/docs/wildfire_edu.htm Wildlandfire.com contains a number of resources and links concerning wild land fires. http://interwork.sdsu.edu/fire/index.htm San Diego Wildfire Education Project: In October 2003, three simultaneous wildfires, the largest and most deadly in the history of California, destroyed 2,400 homes, killed 16 people, and charred 376,000 acres in San Diego County. Then again in October 2007, nine simultaneous fires of varying sizes burned throughout the county requiring the evacuation of 300,000 people and resulting in the loss of more than 1,800 homes and many other structures, 369,600 acres, and 9 fire-related deaths. Local firefighting costs in 2007 topped $80 million. The primary purpose of this environmental education initiative is to educate and motivate individuals most directly affected by the fires in terms of understanding and monitoring the multi-faceted environmental recovery process, with special emphasis on source and run-off pollution, watershed and habitat restoration, and species recovery. http://activefiremaps.fs.fed.us/conus/viewer.htm


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MODIS Active Fire Maps of Conterminous United States http://www.firedetect.noaa.gov/viewer.htm NOAA Satellite Services Division Fire Products: Analyzed Fires and Smoke from Satellite on ArcIMS. http://pubs.usgs.gov/fs/2006/3015/ Wildfire Hazards—A National Threat Wildfires are a growing natural hazard in most regions of the United States, posing a threat to life and property, particularly where native ecosystems meet developed areas. However, because fire is a natural (and often beneficial) process, fire suppression can lead to more severe fires due to the buildup of vegetation, which creates more fuel. In addition, the secondary effects of wildfires, including erosion, landslides, introduction of invasive species, and changes in water quality, are often more disastrous than the fire itself. National Preparedness Level Definitions http://www.nifc.gov/nicc/logistics/references/Definition_of_PL_Levels.pdf


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Chapter 14 Impacts and Extinctions Learning Objectives Earth has been bombarded by objects from space since the birth of our planet. Such impacts have been linked to the extinction of many species, including dinosaurs. The risk of impact from asteroids, comets, and meteoroids continues today. Your goal in reading this chapter is to

• know the difference between asteroids, meteoroids, and comets. • understand the physical processes associated with aerial burst and impact craters. • understand the possible causes of mass extinction. • know the evidence for the impact hypothesis producing the mass extinction at the

end of the Cretaceous Period. • know the likely physical, chemical, and biological consequences of impact from a

large asteroid or comet. • understand the risk of impact or aerial burst of extraterrestrial objects and how

that risk might be minimized. Chapter Outline 14. Impacts and Extinctions

14.1. Earth’s Place in Space 14.1.1. Asteroids, Meteoroids, and Comets

14.2. Airbursts and Impacts 14.2.1. Impact Craters Survivor Story 14.1: Meteorites in Chicagoland

14.3. Mass Extinctions Case Study 14.2: Uniformitarianism, Gradualism, and Catastrophe

14.3.1. K-T Boundary Mass Extinction 14.4. Linkages with Other Natural Hazards 14.5. Minimizing the Impact Hazard

14.5.1. Risk Related to Impacts Case Study 14.3: Possible Extraterrestrial Impact 12,900 years ago 14.5.2. Minimizing the Impact Hazard Case Study 14.4: Near-Earth Objects Professional Profile 14.5: Dr. Michaels J.S. Belton


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Chapter Summary Asteroids, meteoroids, and comets are extraterrestrial objects likely to intercept the Earth’s orbit. Small objects may burn up in the atmosphere and be visible as meteors at night. Depending on their size, velocity, and composition, large objects from a few meters to 1000 kilometers in size may disintegrate in the atmosphere in an airburst or hit the surface of Earth. Objects that impact Earth’s surface produce both simple and complex craters. Many craters have yet to be identified because they are severely eroded, on the seafloor, or are buried by younger deposits. Large objects can cause local to global catastrophic damage and mass extinction of life. The best documented impact occurred 65 million years ago at the end of the Cretaceous period (K-T boundary) and likely produced the mass extinction of many species, including the large dinosaurs. Recent studies suggest that an airburst was responsible for the extinction of many large Pleistocene mammals and the disappearance of the Clovis people at the start of the Younger Dryas glaciation. In addition to mass extinctions, impacts and airblasts of large asteroids and comets are likely to cause tsunamis, wildfires, earthquakes, mass wasting, climate change, and possibly volcanic eruptions. The risk from an airburst or direct impact of an extraterrestrial object is a function of its probability and the consequences should it occur. Relatively small events such as the 1908 Tunguska explosion are likely somewhere on Earth about every 100 years. The oceans will receive 70 percent of the impacts and airbursts. A significantly larger event would be capable of causing catastrophic damage to an urban area. Such events can be expected every few tens of thousands of years. Programs such as Spacewatch and NEAT (Near-Earth Asteroid Tracking Project) will, with high certainty, identify NEOs of diameters greater than a few hundred meters at least 100 years before possible impact. With this warning, sufficient time should then be available to intercept and divert the object by use of nuclear explosions or other techniques. There are about 10 million smaller objects (potential Tunguska-type objects) that could produce catastrophic damage to urban areas. Identifying all these objects will be extremely difficult. Thus we are particularly vulnerable to these smaller objects. Answers to Review Questions: 1. Where is Tunguska? What happened there? Why is it important to our discussion of

natural hazards? How often do these events occur? (p. 473) Tunguska is in Siberia. A blue-white fireball with a glowing tail descended from the sky on June 30, 1908, exploding above the Tunguska River Valley with the force equivalent to 10 hydrogen bombs. The explosion was probably heard throughout an area of at least a million square kilometers, and it leveled forests over a 2000 square kilometer area. It is important to our discussion of


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natural hazards because many people assume that natural hazards of any relevance originate on Earth. Events like this one only occur about once every 1000 years.

2. What is the difference between an asteroid, meteor, comet, meteoroid, and meteorite? (pp. 476–477)

Asteroids range in diameter from about 10 m (30 ft) to 1000 kilometers (620 mi). They are composed of either rock material, metallic material, or rocky-metal mixtures. When asteroids break into smaller particles, they may be known as meteoroids, which range in size from dust particles to objects a few meters in diameter. A meteor is a meteoroid that has entered Earth’s atmosphere. If the object actually strikes Earth, then we speak of it as a meteorite. A comet has a glowing tail of gas and dust ranging in size from a few meters to hundreds of kilometers in diameter. They are thought to have rocky cores surrounded by ice and covered in carbon-rich dust. Aside from frozen water, the ice contains carbon dioxide, carbon monoxide, and smaller amounts of other compounds.

3. What are meteorites made of? Comets? (p. 477) Meteorites are made of stone or metal while comets are composed of a rocky core surrounded by ice and covered with carbon-rich dust.

4. Where do comets and asteroids originate? (p. 477) Comets originate from beyond the planet Neptune and were thrown into an area called the Oort Cloud, which lies beyond the Kuiper Belt and extends out as far as 50,000 times the distance from the Earth to the sun. Asteroids originate in the asteroid belt between the orbits of Mars and Jupiter.

5. Describe the general characteristics of an impact crater. How can it be distinguished

from other types of craters? (p. 478) Impact craters are circular or ringed depressions that may have a layer of debris around the rim of the crater. This is referred to as the ejecta blanket, which other craters might not have. Impact craters will also contain breccia (angular pieces of rock cemented together). Deformation of rocks (high pressure modifications) in the crater can also identify an impact site.

6. How do simple and complex impact craters differ? (p. 480) Simple craters are typically small, a few kilometers in diameter. Complex impact craters experience the same processes of vaporization, melting, ejection of material, formation of ejecta rims, and later infilling typical of simple


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craters, but the shape of a larger, complex crater may be quite different. Following impact, complex craters may grow to sizes of tens of kilometers to more than 100 km (60 mi) in diameter. The rim collapses more completely and the central crater uplifts following impact.

7. Why does Earth apparently have so few impact craters? (pp. 480–481) Ancient impact craters are difficult to identify because they are commonly either eroded or filled with sedimentary deposits that are younger than the impact. Most impact sites on Earth are in the ocean where craters are subsequently buried by marine sediment or destroyed by plate tectonic processes. Additionally, smaller meteoroids and comets tend to burn up and disintegrate in Earth’s atmosphere before striking the surface.

8. Explain the significance of Comet Shoemaker-Levy 9. (pp. 482–484)

This comet impacted Jupiter, releasing between 10,000 and 100,000 megatons of energy (more than all of the Earth’s nuclear weapons detonated at once). This was evidence that a large impact would be catastrophic if it hit Earth. From this point on it is more commonly accepted that comets pose a threat (although the chances are minimal) to the Earth.

9. What is the significance of Barringer Crater? (pp. 484–485)

Known as a “Meteor Crater,” this impact crater in Arizona created a lot of debate about its origin when it became widely known in the late nineteenth century. Its impact origin was later established through careful study and evaluation.

10. What are the hypotheses for the cause of mass extinctions? (p. 485) Some hypotheses for mass extinction are rapid climate change, plate tectonics, volcanic eruptions, and impact of comets or meteorites with Earth.

11. When was the greatest mass extinction in Earth history? (p. 485)

The greatest mass extinction in Earth’s history occurred approximately 446 million years ago at the end of the Ordovician Period.

12. Summarize the causes for the six major mass extinctions in Earth history. (pp. 485–

487)

Most of the major mass extinction events in Earth history are believed to have been related to climate changes. The earliest mass extinction, approximately


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446 million years ago, began when the climate cooled and again when the climate warmed following the glacial interval. The next mass extinction, at the end of the Permian period, about 250 million years ago, may have been caused by global cooling, followed by rapid global warming and large variations in climate. Volcanoes producing massive eruptions spewed tremendous amounts of volcanic ash and gases in the atmosphere, contributed to the cooling. The third mass extinction at the Triassic-Jurassic boundary, 202 million years ago, also appears to have been related to volcanic activity and climate change. Large amounts of carbon dioxide were released from basaltic volcanic eruptions, and Earth’s temperatures increased, resulting in the extinction of plants and animals on land and in the ocean. A fourth mass-extinction event took place at the end of the Cretaceous period and the beginning of the Tertiary period. Known as the K-T boundary, this sudden event was most likely caused by the impact of a giant asteroid, and brought an end to the large dinosaurs. A fifth mass extinction took place near the end of the Eocene epoch about 34 million years ago. Some evidence points to an asteroid or comet impact, but most scientists link this extinction to climate change brought about by plate tectonics. The final mass extinction occurred near the end of the Pleistocene epoch, with the extinction of mammals, reptiles, amphibians, birds, fish, and plants continuing today. Evidence indicates it was brought on by an airburst of an asteroid or comet, and is sustained by human activities that include loss of habitat from land-use changes and global warming, widespread deforestation, and the application of pesticides and other chemicals.

13. What is the K-T boundary? Why is it significant in the study of natural hazards?

(pp. 487–491) The K-T boundary separates the end of the Cretaceous and beginning of the Tertiary. The mass extinction event at this boundary (including the death of the dinosaurs) is thought to have been completed by a meteorite impact, though the environment was stressed from volcanic eruptions and diverging plates before the impact. The impact of the asteroid led to a global catastrophic killing. Should such an event occur again, the loss of species would be immense.

14. How are other natural hazards linked to extraterrestrial impacts and airbursts? (p.

491)


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Natural hazards such as tsunamis, wildfires, earthquakes, mass wasting, climate change, and possibly volcanic eruptions are directly caused by the impact or airburst of an asteroid or comet.

15. Explain how the risk of dying from an asteroid impact is greater than the risk of a

car accident. (pp. 491–494) Computer-run simulations approximate that asteroid impacts account for about 450 deaths in a year. If a catastrophic event killing millions of people is factored into this statistic then there is approximately a 0.01 percent to a 0.1 percent chance that you will die from an impact. There is, by comparison, a 0.008 percent chance you will die in a car crash. However, this is assuming that a catastrophic event happens.

16. What can be done to minimize the extraterrestrial impact hazard? (p. 495)

Spacewatch has been keeping an eye on the skies to alert of any incoming asteroids. The Near-Earth Asteroid Tracking project (NEAT) was set up to identify objects with a diameter of about 3300 feet or greater. People could try to divert the object if one does come too close to Earth. Another option is evacuation of Earth, if ample warning is provided.

Answers to Critical Thinking Questions: 1. Describe the likely results if a Tungska-type event were to occur over or in central

North America. If the event were predicted with 100 years’ warning, what could be done to mitigate the effects, if changing the object’s orbit were not possible? Outline a plan to minimize death and destruction.

A Tungska type event could devastate North America, burning thousands of square miles, and sending huge seismic waves around the world. Humans could attempt to blow up the object into small pieces which would burn up upon entry into the Earth’s atmosphere. Humans could also evacuate the projected impact site, relocating people to other places.

2. How would the effects of an asteroid impact in water differ from those of an asteroid

impact on land? Consider what would happen physically and chemically with water and how the impact craters might differ.

A water impact would cause a tsunami that would destroy property and possibly end lives of millions of people. The water column would vaporize during the impact, sending huge quantities of water vapor into the atmosphere, and contributing to sudden global warming.


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3. Compare the velocity of an asteroid or comet, seismic waves, and the velocity of

sound waves. Why do they differ?

Meteorites hit the Earth with velocities typically in the range of 11–30 km/sec, and seismic waves travel at 3.5–7 km per sec. The speed of sound is about 3.4 kilometers per second at sea level, so these three phenomena all have approximately similar (order of magnitude) values.

4. How did the effects of the impact at the K-T boundary differ from the airburst at the

Younger Dryas boundary? How were the two events similar?

K-T boundary is well documented. This event produced the third largest crater on Earth and provides a good example of the effects of a catastrophic impact—a blast-produced shock wave, fallout of ejecta, a large tsunami (up to 1000 feet high), global wildfires, dust loading in the atmosphere, and finally a collapse of ecological food chains in the ocean and on land. This event was sudden and most likely caused by the impact of a giant asteroid. The K-T extinction brought an end to the large dinosaurs, which had been at the top of the food chain for 100 million years or more. Their demise allowed small mammals to diversify and evolve into the approximately 4000 species, including humans, that are alive today. Evidence of the KT event can be found worldwide. Whereas the air burst of the Younger Dryas boundary as of to date scientists cannot find the impact of a crater. Evidence of this airburst can be found all over North America. It contributed to the extinction of large Pleistocene mammals and the Clovis civilization. The similarities are that both events either the impact or airburst of an asteroid or comet is a direct cause for a number of other natural hazards including tsunamis, wildfires, earthquakes, mass wasting, climate change, and, possibly, volcanic eruptions. Most impacting objects land in the world’s oceans, and large objects will cause tsunamis. The asteroid that hit the Yucatán Peninsula close to 65 million years ago created large, complex tsunamis that spread across the Gulf of Mexico and are recorded in sedimentary deposits in Mexico, Texas, Alabama, and Cuba. Researchers have estimated that 200- to 300-m (660- to 1000-ft.) high waves originated from the impact blast and subsequent landslides in the Gulf of Mexico. Wildfires of regional or global extent have resulted from three well-documented airbursts or impact events: the K-T boundary, the Pleistocene Younger Dryas boundary (see Case Study 14.3), and the Tunguska events. Superheated clouds of gas and debris apparently reach temperatures needed to dry out and then ignite living vegetation. Computer simulations suggest that wildfire patterns following a large impact are complex and involve rock blasted into space that then returns to Earth on the other side of our planet. If it is any consolation, the simulations suggest that the wildfires


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did not burn the entire land surface of Earth. Seismic waves from a large impact most likely activate numerous landslides both on the land and under water. For example, the asteroid that formed the Chicxulub impact on the Yucatán Peninsula appears to have produced a M 10 earthquake and caused the mass wasting of the continental slope of North America as far north as the Grand Banks of Newfoundland. Both the asteroid that created the Chicxulub Crater at the K-T boundary and the probable airburst at the end of the Pleistocene Epoch (see Case Study 14.3) caused global changes in climate. Impacts on land can inject large quantities of dust into the atmosphere. This dust, combined with smoke from wildfires, would result in global cooling for a number of years after any major impact. The global cooling would then be followed by prolonged global warming from the large amounts of carbon dioxide and other greenhouse gases produced by post-impact wildfires. Extraterrestrial impacts have also been hypothesized to produce large volcanic eruptions by causing melting and instability in Earth’s mantle. This melting could result in huge eruptions of lava, referred to as flood basalts, and create large igneous provinces on land. These provinces contain 100 times more lava than that from any historic volcanic eruptions. In the geologic past, these eruptions appear to have produced global changes to the atmosphere and oceans and contributed to major extinctions of life.

Suggested Activities 1. Take a baseball or rock and throw it into a deep layer of mud. Observe the geometry

of the crater, and compare it to simple impact craters. Additional Resources (media, films, articles, journals, web sites) Print Resources Dealing with Impact Catastrophes and Disasters Albritton, C.C. Jr., 1989, Catastrophic Episodes in Earth History, London, Chapman and

Hale. Alvarez, W., 1997, T. rex and the Crater of Doom, Princeton, Princeton University Press,

236 pp. Burke, K., 1988, Tectonic evolution of the Caribbean, Annual Reviews of Earth and

Planetary Sciences, 16, 201–230.


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Chang, K., 2002, Planet or no, it’s on to Pluto, Science Times, The New York Times, Jan. 29, D1, D4.

Chapman, C.R., and Morrison, D., 1994, Impacts on the Earth by asteroids and comets: Assessing the hazard, Nature, 367, 33–39.

Cohen, J.E., 1995, How Many People Can the World Support? New York, W.W. Norton and Co.

Dawson, J.B., 1980, Kimberlites and their Xenoliths, New York, Springer-Verlag. Diamond, J., 1999, Guns, Germs, and Steel, The Fates of Human Societies, W.W. Norton

and Co., New York, 480 pp. Eldredge, N., 1997, Fossils: The Evolution and Extinction of Species, Princeton,

Princeton University Press, 240 pp. Erwin, D.H., 1994, the Permo-Triassic extinction, Nature, 367, 231–236. Kusky, T.M., 2007, Hazards from Out of this World, Asteroids and Meteorites, Facts on

File, Hazardous Earth Set. MacDougall, J.D., ed., 1988, Continental Flood Basalts, Dordrecht, Kluwer Academic

Publishers. Mahoney, J.J., and Coffin, M.F., (editors), 1997, Large Igneous Provinces, Continental,

Oceanic, and Planetary Flood Volcanism, Washington, D.C., American Geophysical Union, Geophysical Monograph Series, 100, 438 pp.

Mannard, G.W., 1968, The surface expression of kimberlite pipes, Geological Association of Canada Proceedings 19.

Martin, P.S., and Klein, R.G. (eds.), 1989, Quaternary Extinctions, Tucson, University of Arizona Press.

McCormick, M.P., Thompson, L.W., and Trepte, C.R., 1995, Atmospheric effects of the Mt. Pinatubo eruption, Nature, 373, 399–404.

Melosh, H.J., 1988, Impact Cratering: A Geologic Process, New York, Oxford University Press.

Mitchell, R.H., 1989, Kimberlites, Mineralogy, Geochemistry, and Petrology, New York, Plenum Press, 442 pp.

Moores, E., 2002, Pre-1 Ga (pre Rodinian) ophiolites: Their tectonic and environmental implications, Geological Society of America Bulletin, v. 114, 80–95.

Poag, C.W., 1999, Chesapeake Invader, Discovering America’s Giant Meteorite Crater, Princeton, Princeton University Press, 168 pp.

Ponting, C., 1991, A Green History of the World, New York, St. Martin’s Press. Rampino, M.R., Self, S., and Stothers, R.B., 1988, Volcanic winters, Annual Reviews of Earth and Planetary Science, 16, 73–99. Renne, P.R., Zichao, Z., Richards, M.A., Black, M.T., and Basu, A.R., 1995, Synchrony

and causal relations between Permian Triassic boundary crises and Siberian flood volcanism, Science, 269, pp. 1413–1416.

Self, S., Thordarson, T., and Keszthelyi, L., 1997, Emplacement of continental flood basalt lava flows, in Mahoney, J.J., and Coffin, M.F., Large Igneous Provinces, Continental, Oceanic, and Planetary Flood Volcanism, Geophysical Monograph 100, pp. 381–410.

Sepkoski, J.J., Jr., 1982, Mass Extinctions in the Phanerozoic Oceans: A Review, In Patterns and Processes in the History of Life, Amsterdam, Springer-Verlaag.


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Sharpton, V.L., and Ward, P.D., 1990, Global Catastrophes in Earth History, Geological Society of America Special Paper 247.

Sheridan, M.F., and Wohletz, K.H., 1983, Hydrovolcanism, basic considerations and review, Journal of Volcanology and Geothermal Research, 17, 1–29.

Stanley, S.M., 1987, Extinction, New York, Scientific American Library. Stanley, S.M., 1986, Earth and Life Through Time, New York, W.H. Freeman and Co.,

690 pp. Wyllie, P.J., 1980, The origin of kimberlite, Journal of Geophysical Research, 85, 6902–

6910. Nonprint Resources Dealing with Catastrophes and Disasters Videos: Asteroids: Deadly Impact, National Geographic Society, 1997, 60 minutes. The Death of the Dinosaur, Public Broadcasting System (PBS), 1990, 60 mins. The Doomsday Asteroid, NOVA/BBC, 1995, 60 minutes. Web sites: http://web.ukonline.co.uk/a.buckley/dino.htm Web site offers short summaries of some theories of dinosaur extinction, including meteorite impacts. Description of impact craters with pictures and illustrations of their known localities on Earth. Web site explains the possible iridium spike in Earth’s crust due to meteorite impacts, and the importance of the K-T boundary in supporting impact structure hypotheses. Frequency of such impacts on Earth are given in terms of years and size of impact. http://www.impact-structures.com/ This site offers information on the research of the geology, geophysics, and petrology of impacts structures. Pictures and links to local European impact structures can be found at this site. The site is maintained by Kord Ernston of the University of Wurzberg. http://personals.galaxyinternet.net/tunga/ Describes the effects of an impact of a comet with Earth, and what we might do to prevent or prepare for future disasters of this sort. http://www.solarviews.com/eng/asteroid.htm Views of the solar system, including the asteroid belt, a web site by Calvin J. Hamilton. http://www.stemnet.nf.ca/CITE/dinodisappear.htm


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This web site provides answers for the common questions of dinosaur extinction. The disappearance of the dinosaurs is correlated to catastrophic events that impacted Earth during their known existence. Such catastrophes such as celestial impacts, volcanoes, and sea level change are addressed as possible causes for the dinosaurs’ extinction. The dates of known catastrophic events are given as possible extinction causes. The web site is created and maintained by Jim Cornish. Organizations Dealing with Impact Catastrophes, Disasters, and Potential Impacts NASA NASA Near-Earth Object Program Jet Propulsion Laboratory 4800 Oak Grove Drive Pasadena, California 91109 818-354-4321 http://neo.jpl.nasa.gov/ In 1998 NASA initiated a program called the “Near-Earth Object Program,” whose aim is to catalog potentially hazardous asteroids that could present a hazard to Earth. This program uses five large telescopes to search the skies for asteroids that pose a threat to Earth, and to calculate their mass and orbits. So far, the largest potential threat known is from asteroid 99AN10, which has a mass of 2.2 billion tons and may pass within the orbit of the moon, at 7:10 a.m., August 7, in the year 2027. NASA has another related program called “Deep Impact,” which is designed to collect data on the composition of a comet, named Tempel 1, which will be passing beyond the orbit of Mars. The comet is roughly the size of mid-town Manhattan, and the spacecraft will be shooting an object at the comet to determine its density by observing the characteristics of the impact. http://impact.arc.nasa.gov// This web site from NASA’s Ames Research Center describes various hazards associated with asteroid and comet impacts with Earth. Includes related information on astrobiology and near-Earth objects. Governmental research and Congressional legislation regarding NASA policy on celestial impacts are provided and discussed. http://www.unb.ca/passc/ImpactDatabase/ The Geological Survey of Canada has compiled an Earth Impact database, available at the site above. The database is regularly maintained, and contains maps and images of various impact craters. For more information, contact: Dr. John Spray ([email protected]), Director, PASSC Planetary and Space Science Centre, Department of Geology, University of New Brunswick, 2 Bailey Drive, Fredericton, NB, Canada, phone: 506-453- 3550, e-mail: [email protected]. Lunar and Planetary Laboratory, University of Arizona http://seds.lpl.arizona.edu/nineplanets/nineplanets/meteorites.html Web site has extensive list of information about meteors, meteorites, impacts, and links to other sites. Site is run by the Students for the Exploration and Development of Space


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(SEDS). UA SEDS, Box 174 Space Sciences Building, The University of Arizona, Tucson, Arizona 85721, phone: 520-621-9790, fax: 520-621-4933, e-mail: [email protected].

instructor’s manual for e...natural processes such as volcanic eruptions, earthquakes, floods, and...

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