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The Good Earth/Chapter 10: Landslides and Slope Failure

“The term ‘natural disaster’

has become an increasingly

anachronistic misnomer. In

reality, human behavior

transforms natural hazards

into what would really be

called unnatural disasters.”

- Kofi Annan,

Secretary General of the United

Nations

Would you live

here?1

ESC1000 • Earth Science • Summer 2016Chapters 6-10

Announcements• Office hours this week:

– Today 3-4 pm

– Friday 4-5 pm

• Exam 2 on Monday

– Again, 25 multiple-choice, true-false; 45 minutes; reference sheet that

I’ll provide -- with different precautions to protect honesty.

– Material emphasized on exam will be announced tomorrow on the

website (depends on what we cover today).

• To start:

– Review study guide and work on one or two questions from Chapters

6, 7, and 9; and list one or two questions that you want to review from

Chapters 8, 10, and 11.

– I will return your activities and course grades so far, while you do this.

– One Plate Tectonics Activity does not have names on it – please

identify yourselves.2

Room 3348

Building 3, 3rd floor

Shared adjunct faculty office

(aka “Idea Center”)

Mont Pelée, Martinique

https://www.youtube.com/watch?

v=B58V2ZEsMVI&list=PLsR2Pq

V04jSqBL1ZaBx65YrUMRYkY0p

PS&index=6

https://www.youtube.com/watch?v=-

XejSECLqVQ&list=PLsR2PqV04jSqBL1ZaBx65YrUMRYkY0pPS&index=2

https://www.youtube.com/watch?v=9kFtXXuoR1U&list=PLsR2PqV04jSq

BL1ZaBx65YrUMRYkY0pPS&index=3

Before 1902 eruption:

After 1902 eruption:

Documentary (intro is from 1991 eruption in Japan that killed volcanologists

Maurice and Katia Krafft)

https://www.youtube.com/watch?v=c5CAyaRIW8s 3

https://www.youtube.com/watch?v=B58V2ZEsMVI&list=PLsR2PqV04jSqBL1ZaBx65YrUMRYkY0pPS&index=6

https://www.youtube.com/watch?v=-XejSECLqVQ&list=PLsR2PqV04jSqBL1ZaBx65YrUMRYkY0pPS&index=2

https://www.youtube.com/watch?v=9kFtXXuoR1U&list=PLsR2PqV04jSqBL1ZaBx65YrUMRYkY0pPS&index=3

https://www.youtube.com/watch?v=c5CAyaRIW8s

Different plate locations make magma from melting different rocks.

The Good Earth/Chapter 6: Volcanoes and Other Mountains

Types of Magma:

1. Basaltic

2. Rhyolitic

3. Andesitic

3

12

Types of magma:

Basalt: oceanic mantle rocks melt

Rhyolite: continental crust melts

Andesite: mantle rocks melt4

Examples of different magma types,at different volcanoes.

The Good Earth/Chapter 6: Volcanoes and Other Mountains

Oceanic Hot spotBasaltic magma

Divergent Boundary

Continental RiftBasaltic & Rhyolitic

magma

Convergent Boundary

Oceanic Trench/

Subduction ZoneAndesitic magma

5

Review – Volcanoes ActivityKilauea Nyiragongo Pelée St. Helens

Volcano

Type

Shield

volcano

Stratovolcano

Cinder cone

Stratovolcano Stratovolcano

Type of

Magma

Basaltic, low

viscosity

52% silica,

0.5% water

Andesitic

Basaltic Andesite and

basaltic

Pyroclastic

rocks

Pyroclastic?

Basaltic

Layers of basalt

and andesite,

also rhyolitic;

64% silica; 4%

water

Plate

boundary

or hot

spot

Hot spot Hot spot?

(Future)

divergent

boundary

Convergent:

North American

& Caribbean

plates

Convergent

(Ring of Fire);

Triple plate

junction of

Pacific, N. Amer,

Juan de Fuca

6

In-Class Activity 3, Part B

Evaluate the scientific evidence (if any) presented

in the video about the Yellowstone Super Volcano:

https://www.youtube.com/watch?v=ePn4LLrNqrY

1. What does this video tell you about how

volcanoes erupt?

2. Do you think that a super volcano is likely to

erupt in Yellowstone National Park, in your

lifetime? Why or why not?

3. How does the “Yellowstone Super Volcano”

compare to one of the other volcanoes you learned

about today?

?7

https://www.youtube.com/watch?v=ePn4LLrNqrY

Checkpoint 6.6, p. 146

Venn Diagram: Magma Composition and Magma Sources

Use the Venn diagram provided to compare and contrast the compositions and sources of the 3 principal

types of magma. Write the numbers corresponding to features unique to either group in the larger areas

of each circle; note features that they share in the overlap areas.

1. Low silica content

2. From a mantle source

3. Example: Aleutian Island volcanoes

4. High silica rock (Rhyolitic)

5. Intermediate silica rock (Andesitic)

6. Example: Hawaiian Islands (Basaltic)

7. High melting temperature (Basaltic)

8. Lowest melting temperature (Rhyolitic)

9. Most common at convergent plate boundaries (Andesitic)

10. Contains silica (all three)

11.Produced by most active volcanoes (Andesitic)

12.Formed due to plate tectonic processes (All)

13.Most commonly formed at divergent plate boundaries (Basaltic)

14.Produced by decompression melting (Basaltic)

15.Magma source rock--mantle (Basaltic)

16.Melting occurs due to addition of water (Andesitic)

17.Magma source rock--oceanic lithosphere (Andesitic)

18.Magma source rock--continental crust (Rhyolitic)

19.Produced by addition of heat (Rhyolitic)

20.Example: Yellowstone (Rhyolitic)

5, 9, 11, 16,

17

6, 7, 13, 14,

15

10

12

4, 8, 18,19,

20

Magma Composition and Magma Sources

Weathering Checkpoints-

from Study GuideImagine that you have been appointed to a team of researchers charged with

determining which of the five World Heritage sites in Figure 9.1 is at greatest

risk from physical, chemical, and biological weathering. For each type of

weathering, identify at least three general questions you will ask as you begin

to gather data for your study.

The Good Earth/Chapter 9: Weathering and Soils

9

Weathering Rates of World Heritage Sites

The Good Earth, Chapter 9: Weathering and Soils

Evaluate how these different factors make structures more, or less, resistant to

weathering.

For example, rock type:

Granite = most resistant

Sandstone = less resistant

Limestone = weak rock 10

Review – Weathering QuestionsPhysical Chemical Biological

Is there a source of

pressure?

How acidic is the

precipitation?

What types of vegetation

would break rocks?

Do cold climates cause

rocks to break?

Why do rocks near the

ocean have a slippery

surface? (also biological)

Under which conditions

would moss grow?

If water seeps into porous

rocks, does this cause them

to expand?

What does the specific

rock type react with,

chemically?

(ex: limestone + acid)

Is most life in the area

macroscopic or

microscopic?

How does altitude influence

physical changes?

How fast does pollution

damage structures?

How many tourists visit

each day? (and are they

well-behaved?)

How much exposure to

sunlight occurs here?

(sun = heating)

How does oxygen

chemically alter rocks?

(and does altitude

matter?)

11

Other good questions

• How is weathering different from erosion?

• How can a tree be strong enough to break a rock?

• Why is there more chemical weathering in warm and wet

climates?

• How are biological and chemical weathering related?

• How do people cause biological weathering?

– Ex: coral reefs in the Keys and Cuba

(Local NPR piece, 7/12)

12

Weathering Rates


What controls how quickly a rock weathers?

Rock composition

Rock properties

Climate

In these low porosity rocks, weathering is

restricted to the outer rind.

Weathering concentrated along fractures.

The degree of weathering decreases

downward. Why?

13

Weathering Rates


Composition as a variable

1. Weathering is faster in rocks composed of weaker material

or material that is easily converted to weaker material (such

as feldspars)

2. Weathering is faster in rocks made up of minerals that

dissolve in water (salt, gypsum)

3. Weathering is slower in rocks made of resistant materials

(quartz)

Rock property as a variable

1. Weathering is faster in rocks that allow air and water in

(porous, fractured)

2. Fractures are natural weathering surfaces

3. Igneous and metamorphic rocks generally have low porosity

– do you think they are particularly susceptible to

weathering?14

Weathering Rates


Climate as a variable

(Climate = a region’s average annual temperature,

precipitation, and vegetation)

1. Chemical weathering is faster in warmer climates

2. More water (rain, humidity) = more dissolution and hydrolysis

reactions

3. More shade provided by vegetation can impede evaporation

and allow more water to find its way into cracks thereby

increasing rates of weathering

4. Carbon dioxide released from plants can combine with water

to make carbonic acid

5. Higher elevations may have more freeze/thaw cycles,

increasing rates of physical weathering

6. Extremely cold regions don’t have much thawing, therefore

not much wedging occurs 15

Chapter 8: Geologic Time

Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

1.

2.

3.

4.

5.

Thinking About Time

The History of (Relative) Time

Geologic Time

Numerical Time

Rates of Change

The following slides are from my

Oceanography course.

See the study guide for the relevant

questions from your textbook.

16

As Earth continued to cool,

volcanic activity caused “outgassing”

of many substances, especially

water vapor.

Outgassed water vapor eventually

condensed to liquid.

The first oceans were born …

about 4.5 billion years ago.

The Earth is approximately

4.55 billion years old.

17

Comet impacts may have also added water and organic compounds to ocean.18

Life on Earth originated about

3.5 billion years ago.

The first life forms were likely

anaerobic – they survived without

oxygen (and perhaps in the dark).

Cyanobacteria:

Early life forms

(Later) produced oxygen

- aerobic

Now dominate the ocean

Microbial mats

(living)

formed

stromatolites

(fossils)

19

Did life originate at

hydrothermal vents?

• All life depends on salty

water within its cells to

dissolve and transport

chemicals.

• Water holds heat.

• Water moderates

temperatures.

• Water suspends

nutrients and wastes.

We believe that life began in the oceans.

20

Earth’s atmosphere responded to this life.21

Geological Time

First

life form

Bacteria began to

produce oxygen

“Oxygen revolution” 22

See study guide for

more information…

Exam question on geologic time

Adriana Ocampo

Her research led to the

discovery of the site

where the dinosaur-killing

asteroid hit Earth

(Chicxulub, MX). 23

Chapter 10: Landslides and Slope Failure

Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

1. Mass Wasting: The Human

Impact

2. Factors Influencing Slope

Failure

3. Slope Failure Processes

24

Mass Wasting: The Human Impact


If there is no human impact caused by a natural phenomenon, there is no disaster.

Jan 10, 2005 – in a matter of seconds a 330 foot portion of the slope mobilized,

flowed down, and buried homes and killed ten people.

“It came down like lava down the mountains. It was explosive, like there was a stick

of dynamite in there.” (A resident of La Conchita)

25



Mass Wasting = the downslope movement of

material under the influence of gravity.

Thicker regolith is more

likely to fail

Mass wasting is key in

modifying landscapes in

areas with significant

topography

Beartooth Mountains, southern Montana

Similar terms:

Landslide

Mass wasting

Slope failure

26



Where do

you see the

areas of

highest risk

for slope

failure? What

do those

areas have in

common?

Orange and brown = high to moderate incidence

Gold = high susceptibility but moderate incidence27

Mass Wasting: The Human Impact Self Reflection Survey

Answer the following questions as a means

of uncovering what you already know about

landslides and slope failure.

A. Are there places in your community that

are characterized by steep slopes? Have

landslides occurred there?


28

Factors Influencing Slope Failure

The Good Earth/Chapter 10: Factors Influencing Slope Failure

Gravity moves materials

down a slope

Friction acts to prevent or

slow the movement of

material down a slope

• Steeper slopes are more likely

to fail

• Analogy – a slide on a

playground

− The steeper and smoother the

slide, the faster you go

Steep slopes in Sierra de Avila

(Venezuela) allow material to wash

into narrow canyons that funnel

debris toward coastal cities. The

bare patches are locations where

landslides have occurred.

29



Water: A small amount of water holds grains together

(cohesion)

Dry sand slopes

will fail above

angles of about 35

degrees

Too

much

water

forces

grains

apart30



Too much water promotes instability

• Very wet sediment flows like a liquid

• Excess water reduces cohesion between grains and

allows them to move more freely

• Adds weight to a slope

Example: Higher risk for landslides in the Appalachian Mountains

than in the western states where slopes are steeper. Why?

More precipitation in the eastern U.S. Addition of water to slopes

with loose materials increases the likelihood of failure.

31



Venezuelan Landslides

• The view from the Caribbean Sea

− The mountains of the Sierra de

Avila with the city of

Caraballeda in the foreground

View up a canyon from

Caraballeda showing narrow

canyon floor and steep sides32

Landslides and Slope Failure


• What happened in Venezuela in 1999?

− Unseasonable storms – 36 inches of rain on steep mountain slopes

− A series of floods and landslides devastated communities along the

coast and killed ~19,000 people

− The 3-day rainfall total equaled the average annual rainfall in

midwestern U.S.

− Vegetation had shallow roots in the 10 ft thick soil/regolith

− Cities were located on the only flat patches of ground – at the

mouths of the narrow canyons, where material was funneled

− Slurries of dirt, rocks, and water flowed at velocities of 6-30 mph

− Flows were fast enough to carry bus-sized particles

33



• 16 ft thick deposits on canyon floor

• Caraballeda

− Single story buildings were buried

− About 10% of the population of the

Vargas State died in this event (also

called the Vargas Tragedy)

− Apartments partially collapsed

− Over 140,000 people homeless

− Burial of main road impeded

evacuation

− Poor city planning, construction

standards, building inspections

− Cost of damage $2 billion

34



• Human influence

− Venezuela – very little urban planning

− La Conchita – earlier slide blamed on overwatering of crops

above the bluff

List as many factors as you can that contributed to the debris

flows in Venezuela in December 1999.

35

Factors Influencing Slope Failure Checkpoint 10.3

The Good Earth, Chapter 10: Landslides and Slope Failure

1. Caused by excessive rainfall

2. Happened in an area with strict

planning and construction

standards

3.

4.

5.

6.

7.

8.

La Conchita Caraballeda

Venn Diagram: La Conchita vs. Caraballeda

LandslidesUse the Venn diagram to compare and contrast

mass wasting events at La Conchita and

Caraballeda. Write the features in the list at left,

and place their corresponding numbers in either of

the circles (depending on which landslide they refer

to) or in the overlap (if they refer to both).

1

2

36



Can we minimize slope failures? How?

• Improve slope

drainage

• Attach the

slope material

to bedrock with

physical

restraints

37

Slope Failure Processes


38



Mass Wasting is characterized by type of

material involved (rock versus regolith) and

manner of movement.Rockfall – The dislodging of a rock from a steep slope.

39



Rockslides – Large-scale movements of rock traveling rapidly down a

slope along a surface

40



Slump – The movement of

material down a slope on a

curved slip surface

Debris Flow – Material flowing

downhill as a chaotic mixture of

soil, rock, and water

41

Slope Failure Processes Checkpoint 10.6

Examine the following diagram and answer the following questions. Assume

that this diagram is from an area in the midwest (Illinois or Indiana).

1. The road cut in this diagram is likely

to experience mass wasting by

which process?

a. Rockfall c. Slump

b. Rockslide d. Debris flow


42

Slope Failure Processes Checkpoint 10.6

Examine the following diagram and answer the following questions. Assume

that this diagram is from an area in the midwest (Illinois or Indiana).

2. If the swimming pool on the right side of

the diagram leaks, the underlying dirt

fill is likely to experience mass

wasting by which process?

a. Rockfall c. Slump

b. Rockslided. D. Debris flow


43

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