geoscenario resources—glaciers: geologist · 2019-04-11 · reflectivity of earth’s...

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Glaciers— of 8Version date November 20, 2018

Geoscenario Resources—Glaciers: GeologistTaskNow that you have explored as a team the general story of how glaciers shaped the midwestern and northeastern United States, it is time for each of you to dive into more specialized information. The geologist focuses on regional features shaped by glaciers and how they formed. Add helpful details to your notes for Geoscenario Team Questions. Then work together and combine all the information to successfully present your story of glaciers.

Questions for the Geologist to Consider• What geological features in this region were formed by glaciers?• What is the geological story of how the features were formed?

InformationOver a period of 10,000 years (100,000–110,000 years ago), the temperature dropped about 17°C, and the most recent glacial period began (evidence from oxygen ratios and foraminifera data). Around 20,000–35,000 years ago, the Laurentide (or Wisconsin) Ice Sheet covered most of Canada and a large portion of the northern United States.

The massive ice sheet scraped away layers of earth materials as it pushed southward. Geologists look for clues today that help them determine the path and rate of glacial movement. The Great Lakes fill basins that the glaciers carved. In other areas, exposed rock displays scrape marks created by advancing ice carrying rocks and debris, called glacial till. Piles of glacial till form landmarks like moraines. Even huge boulders can be carried by glaciers. When geologists spot a boulder in an unexpected place, called an erratic, they often suspect a glacier carried it there.

A glacier pushing poorly sorted glacial till in front of it. The glacial till forms a moraine. © iStockphoto/cotesebastien

Glacial till being carried along by a glacier as it moves down the valley. As the glacier melts (near bottom of the picture), it deposits till that forms moraines along the sides and in the middle of the glacier. © Bruce Molnia, Terra Photographics

A glacier moved over this bedrock. Rocks embedded in the glacier dug these grooves, or striations, in the bedrock. The grooves show which way the glacier was moving. Courtesy of US Geological Society



14,000 Years Ago

I C E

I C E

9,000 Years Ago

Early LakeOntarioEarly Lake Erie

LakeAlgonquin

Lake Chicago

Lake Maumee

Here are some things to think about that should be part of your story of this region.

• Look at the images above. Why didn’t the meltwater flow out the St. Lawrence River 14,000 years ago, as it does today?

• Look at the rock column to the right. What happened to the rock in the Great Lakes basin that was less than 400 million years old?

Events25,000–20,000 years ago: Glaciers advancing from the Laurentide Ice Sheet carve out the Great Lake basins.

21,000–18,000 years ago: Terminal moraines deposit at the southern edge of the glaciers in northeastern and midwestern United States.

18,000 years ago: Oldest seashells on Long Island and Cape Cod.

11,000 years ago: Glaciers retreat to just north of the St. Lawrence River. Water flows out of the St. Lawrence River. Water levels in Lake Ontario and Lake Erie suddenly drop to about the level they are today.

Vocabularyerratic boulder out-of-place boulder composed of rock that is different from the bedrock or other area rock

glacial till poorly sorted earth materials that are carried and deposited by glaciers

A rock column from a Great Lakes basin. The top layer is glacial till (a few thousand years old) directly on top of Silurian rock, which is over 400 million years old. (Undifferentiated layers cannot be precisely aged.)Courtesy US Geological Survey.

These maps show the retreat of the Laurentide Ice Sheet. The meltwater level in the Great Lake basins 14,000 years ago was much higher than it is today.Courtesy National Oceanic Atmospheric Administration.

St. Lawrence River

moraine a mound of glacial till that is deposited around at the edges of an advancing glacier

terminal moraine a mound of glacial till that is deposited at the front end of a glacier

St. Lawrence River



Geoscenario Resources—Glaciers: GlaciologistTaskNow that you have explored as a team the general story of how glaciers shaped the midwestern and northeastern United States, it is time for each of you to dive into more specialized information. The glaciologist notes focus on how glaciers form, advance and retreat, and what information glaciers can provide about past environments. Add helpful details to your notes for the Geoscenario Team Questions. Then work together and combine all the information to successfully present your story of glaciers.

InformationGlaciers store about 69 percent of the world’s fresh water. Almost 10 percent of the world’s landmass is currently covered with glaciers, mostly in Greenland and Antarctica.

Glacier FormationGlaciers can form when more snow falls in the winter than melts during the summer. Snow accumulates and stays year-round at high altitudes and high latitudes. After enough layers of snow accumulate, there is so much weight pushing down on the lower layers of snow that they are transformed into extremely dense layers of glacial ice. If the ice is in a mountain valley, gravity slowly pulls the dense, massive ice toward lower elevations. If it is on flat land, the weight of the ice where it is the thickest will cause the ice on the bottom to flow outward, as seen in the diagram below.

Water from glaciers is constantly melting and refreezing. The water runs into cracks in the bedrock and refreezes and expands, breaking off pieces of the rock. The rocks, boulders, and other earth materials that have frozen in the ice become part of the glacier and are carried along with the glacier as it moves.

Questions for the Glaciologist to Consider• How do glaciers form, advance, and retreat?

• What information do glaciers provide about past environments?

This map shows how much of North America the Laurentide (or Wisconsin) Ice Sheet covered during the last glacial period. The arrows show the flow direction of the ice sheet. Courtesy USGS.

A glaciologist in an ice cave in the Mendenhall Glacier in Alaska. Glacial ice is so dense that only the blue-spectrum light can escape. © Bruce Molina, Terra Photographics

Glaciers are always moving forward. A receding glacier is not moving backward; it is simply melting faster than it is moving forward. A glacier that is building and moving forward faster than it is melting is called an advancing glacier.



Other Interesting Facts • When the climate warmed and the glaciers

began to melt, they produced millions of cubic kilometers of very cold meltwater.

• Moraines from retreating glaciers formed dams that kept the meltwater from flowing south.

• Towering, retreating glaciers formed ice dams that kept the meltwater from flowing north.

• Snow that formed the estimated 70 million cubic kilometers of ice-age glaciers in North America came from water that evaporated from the ocean. This lowered the ocean level worldwide by 130–150 meters.

Stories in the Ice• Each year, snow forms a layer of ice in a glacier.

Ice cores can be drilled and removed from the glacier in order to study the layers.

• Each layer of ice can be analyzed to determine what was happening during the year that the ice accumulated.

• Air bubbles trapped in the ice can hold stories of air temperature and atmospheric concentration of carbon dioxide (CO

2 ),

methane, and sulfur dioxide from volcanic eruptions.

• Ice layers can also tell stories about atmospheric concentrations of volcanic ash and pollen.

• Some ice cores from Antarctica provide a record of over 400,000 years.

Events 20,000 years ago: Glacial ice cores indicate the beginning of a gradual warming trend.

15,000-11,000 years ago: The Laurentide Ice Sheet retreats from the northern United States.

1300-1850: Glacial ice cores show temperatures are 3–8°C (6–14°F) cooler during the 550-year period in North America and Europe.

1815-1816: Volcanic ash and sulfur dioxide gas bubbles are found in glaciers around the globe.

1850 (beginning of the industrial age): Ice-core data show that CO2 in the atmosphere begins to increase.

1950: Direct measurement of the CO2 level in the atmosphere shows a more rapid increase, which continues to the present time.

A glaciologist taking a sample of an ice core.

Courtesy of National Oceanic and Atmospheric

Administration

Notice the layers within the glacier. Courtesy US Geological Survey

Boulders in a small pond of meltwater being carried along on top of a glacier. When the glacier melts, the boulders will be deposited in an area far from where they originated. © iStockphoto/Roman Krochuk

Vocabularyatmospheric CO2 concentration of carbon dioxide gas in the atmosphere

ice cores cylinders of ice that have been drilled out of a glacier

meltwater water from the melting glaciers



Geoscenario Resources—Glaciers: PaleoclimatologistTaskNow that you have explored as a team the general story of how glaciers shaped the midwestern and northeastern United States, it is time for each of you to dive into more specialized information. The paleoclimatologist focuses on how scientists gather clues about past environments and climate, then uses that information to make predictions. Add helpful details to your notes for Geoscenario Team Questions. Then work together and combine all the information to successfully present your story of glaciers.

InformationExtensive research by scientists has established some basic information about the relationship between environmental changes and climate. In the list of factors below, the arrows indicate changes to global temperatures: decrease, increase.

Greenhouse gases, such as Carbon Dioxide (CO2), absorb sunlight and retain heat within the atmosphere, causing an overall warming of the atmosphere. This can have dramatic effects on global weather patterns.

Reflectivity of Earth’s surface—more clouds and glaciers reflect more solar energy back into space and have a cooling effect.

Variations in Earth’s tilt, wobble, and orbit can cause gradual warming or cooling over thousands of years.

Clouds can either warm or cool Earth, depending on their density and altitude. Cloud variability is a source of uncertainty in predictions.

Urban environments create islands of heat from industry, buildings, automobiles, and the absorption of solar energy by dark-colored surfaces.

Reforestation and other habitat restorations can create carbon sinks in which photosynthesis converts CO2 to oxygen gas. Also, forests absorb less surface heat compared to urban areas, grasslands, and deserts.

Interpreting Ice Cores Taken from Glaciers See the glaciologist in your group for more details.• Volcanic ash and sulfur dioxide gas in a layer

indicates a volcanic eruption.

Questions for the Paleoclimatologist to Consider• What factors affect climate and climate change?

• How do scientists gather clues about past climates and use that information to predict future climates?

A drill dome. Courtesy NOAA.

Storing the ice cores in Colorado.Courtesy of USGS.

• Bubbles of gas in each ice layer can be analyzed to determine the greenhouse and volcanic gases that were in the atmosphere when the snow fell.

• The thickness of the layer tells how much snow fell that year.

• The ratio of different oxygen isotopes in the ice indicates the air temperature when the snow formed.

Additional Climate Information• Since the last ice age started (2 mya), there have

been about 18–20 glacial periods (with ice sheets covering much of North America) with warmer interglacial periods in between.

• Since the burning of fossil fuels began in earnest in the 1800s with the Industrial Revolution, atmospheric CO2 levels have increased more rapidly.

• Climate warming usually takes place slowly, at a rate of 1–2 °C every thousand years. However, it can take place over a few years.

• Earth has warmed 1ºC over the last 100 years. It is now warmer than it has been in the past 1,000 years.



August 13, 1941 August 4, 1950 August 31, 2005

These three photographs taken from the same spot show how much Muir Glacier in Glacier Bay, Alaska, has thinned and retreated during 64 years. Most glaciers worldwide have done the same thing. Even the glaciers in Glacier National Park in Montana will probably be gone by the year 2050. Courtesy of US Geological Survey.

• Climate cooling normally takes thousands of years. However, catastrophic events, such as volcanic eruptions and meteor strikes, can cause major global changes in only a few years.

• Chemicals in fossilized coral reefs and fossilized foraminifera shells indicate the water temperature when the coral and forams were living.

• Pollen grains found in seabed cores provide a record of when warm- or cold-weather plants were growing in the area.

Using Computers to Model and Predict Climates• Climatologists develop computer programs that

factor in dozens of variables to model climate.• Data about paleoclimates are fed into

supercomputers to see if the computers can accurately predict future climates.

• As more is learned about factors affecting climates, the computer models have become more accurate.

• Computer models indicate that the rapid warming is due to the increased CO2 in the atmosphere, which is caused in part by increased burning of fossil fuels.

Events2 mya: Seabed cores and foraminifera data indicate a cooling trend and the start of the Ice Age.

100,000 years ago: Over a period of 10,000 years, the temperature drops about 17ºC, and the most recent glacial period begins (oxygen–isotope ratios and forminifera data).

20,000 years ago: Sea level is about 130–150 meters lower than it is now. Most of the continental shelf is exposed.

15,000 years ago: Oxygen-isotope ratios in ice cores, pollen grains in Mexico lakebed core, and ocean cores all indicate the start of a gradual warming trend, with the ice sheet retreating

900-1300: Medieval warm period, with global temperatures similar to today’s temperatures.

1300–1850: The Little Ice Age, with temperatures 3–8ºC cooler.

1816: The average temperature per year in Europe and North America drops an additional 0.4–0.8°C.

1850 (the beginning of the industrial age): Ice-core data shows CO2 in the atmosphere begins to increase.

1950: Direct measurement of CO2 level shows rapid increase, which continues to the present time.

1973–present: The growing season (from the last freeze in the spring to the first killing freeze in the fall) lengthens by 3–4 weeks in temperate regions.

Vocabularyforaminifera microscopic marine animals with a calcareous shell

glacial period a cold period when ice sheets covered much of North America

greenhouse gas a gas in the atmosphere that will absorb and reradiate heat energy

interglacial period warmer periods between glacial periods when the ice sheets retreat

isotope atoms of the same element that have a different atomic weight

mya million years ago

seabed core a cylindrical sample of seabed that is removed with a special drill



Geoscenario Resources—Glaciers: Climate Policy AdviserTaskNow that you have explored as a team the general story of how glaciers shaped the midwestern and northeastern United States, it is time for each of you to dive into more specialized information. The climate policy adviser notes focus on how climate changes have affected the environment and people in the past and how to use that information to make predictions about the future. Add helpful details to your notes for Geoscenario Team Questions. Then work together and combine all the information to successfully present your story of glaciers.

InformationPolicy advisers work with people in various agencies to develop plans to reduce the negative effects of climate change. Policy advisers study • historical data about how weather and climate

changes have affected people;• climate data and predictions to determine how

best to serve the needs of people now and prepare for future climate change.

• Computer-climate models indicate that the increased greenhouse gases are creating a warmer climate. Small changes in temperature cause significant changes in weather patterns.

• Results of increasing global temperatures are causing

• Precipitation patterns become drier or wetter).

• Sea level increases 3 millimeters per year because of water expansion.

• Sea level rises faster as ice sheets in Greenland and Antarctica melt.

• Warmer summer temperatures, put extra stress on people, other animals, food crops, and other plants.

• The growing season is 2–4 weeks longer than it was in 1970.

• Severe storms (tornadoes, floods, hurricanes with storm surges, hail, high winds) are more frequent.

• storm surges destroy coastal wetland habitats and flood low-lying coastal areas.

• Population increases for many insects that carry disease (for humans, plants, and animals, feed on crops, and trees).

• Tropical insect-borne and waterborne diseases (for humans and wildlife) become more widespread.

• Dead trees; dry grass; more wind and lightening; and hotter, dryer summers—all create extreme fire danger.

• Animals and plants go extinct, due to habitat loss from melting ice caps, dying forests, dying coral reefs, and spread of diseases.

• Corals around the world to die from warmer water and acidification. The acidification also prevents plankton and shellfish from forming shells and reduces the survival rate of many young fish.

Future Planning NeedsPublic-awareness campaigns can inform people of the climate changes that are already taking place. These campaigns could also inform people how to reduce activities that produce greenhouse gases, such as implementing policies that encourage the use of alternative-energy sources and conservation of fossil fuels; planting more trees to take in and store more carbon dioxide (CO2); and encouraging the use of more energy-efficient forms of transportation, building, manufacturing, and food production. This is especially important in the United States, which produces more greenhouse gases than any other country on Earth. These measures might prevent some of the consequences of more frequent severe weather, flooding, and storm surges (in coastal areas). • Building seawalls and levees and relocating structures and roads.

Questions for the Climate Policy Advisor to Consider• How have climate changes affected the environment and people in the past?

• How can this information help us plan for the future?

During a hurricane, most damage and loss of life is caused by the storm surge. Courtesy NASA.



Scientists create computer models, using many variables (such as human fossil-fuel use, cultural changes, price of oil or gasoline, car production, and alternative-energy development) predict how our behavior will impact future atmospheric CO2 levels. This graph shows the predicted temperature increases, depending on various levels of CO2 increase. Courtesy of National Oceanic and Atmospheric Administration

If the sea level rose 1.5 meters, the red areas would be flooded. Blue areas would flood if the sea level rose 1.5–3.5 meters. Courtesy of Environmental Protection Agency.

• Changing building codes so that buildings will withstand stronger storms

• Creating zoning laws so that future buildings will not be built in areas that are likely to flood

• Establishing emergency procedures for evacua-tion routes; rescue operations; and community shelters for water, food, medical supplies (to treat injuries and waterborne illnesses), and other basic services.

Climate-change policy should also address• planning for food storage and distribution, in

case of crop failures;• implementing practices that reduce the severity

of wildfires;• training medical personnel to be more familiar

with the diagnoses and treatment of insect-borne and tropical diseases and heat stroke.

Events900–1300: Norse voyagers settle Greenland and parts of North America.

1300–1850 (Little Ice Age): Several famines occur when crops do not survive.Millions in Europe and North America die from epidemics of the bubonic plague, typhoid, and other diseases associated with malnutrition.

1380: Norse settlers abandon most of Greenland. Crops and livestock freeze.

1790–1815: Coal extraction and use of coal increases from 6 to 16 million tons.

1816: A drop of only 0.4–0.8°C in average temperature causes a “year without a summer” in the northern United States and Canada.

Livestock and wildlife starve or freeze, and there is no food to hunt. Thousands of people starve.

1850: Burning coal to power factories and trains begins to increase significantly. The CO2 level in the atmosphere also begins to rise.

1950: Fossil-fuel use begins to rise dramatically, as does the CO2 in the atmosphere.

1995: Rapid expansion of manufacturing and transportation in developing countries, such as China and India, increases CO2 levels even faster.

2009: The Intergovernmental Panel on Climate Change issues a report stating that the climate change taking place is almost certainly being caused by greenhouse gases. However, some people still don’t believe that human activity can cause climate change.

Vocabularyalternative energy usually a nonfossil-fuel form of energy, such as wind, solar, geothermal, or hydroelectric, that does not use fossil fuel.

insect-borne disease a disease carried by an insect (such as malaria, which is carried by a mosquito).

policy an agreed-upon procedure for dealing with a question or issue

storm surge high winds pushing on the ocean’s surface, which push water inland in floods. Most of the fatalities and destruction during a hurricane occur during a storm surge.

waterborne disease a disease carried by an organism that lives in the water.

Global Average Temperature 1900-2100

geoscenario resources—glaciers: geologist · 2019-04-11 · reflectivity of earth’s...

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