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Design an Experiment This lab demonstrated the relationship between exposure time and weathering. Consider other factors that affect weathering. Design an experiment to measure the effects of those factors.

GeoLab 185

Matt Meadows

2 Study Guide

Download quizzes, key terms, and flash cards from glencoe.com.

BIG (Idea

Weathering and erosion are agents of change on Earth's surface.

Vocabulary

Weathering chemical weathering (p. 166) exfoliation (p. 165) frost wedging (p. 164) mechanical weathering (p. 164) oxidation (p. 166) weathering (p. 164)

Key Concepts

MAUWJdSa Weathering breaks down materials on or near Earth's surface.

• Mechanical weathering changes a rock's size and shape.

• Frost wedging and exfoliation are forms of mechanical weathering.

• Chemical weathering changes the composition of a rock.

• The rate of chemical weathering depends on the climate, rock type, surface area, and topography.

Section 7.2

Erosion and Deposition deposition (p. 171) erosion (p. 171) gully erosion (p. 172) rill erosion (p. 172)

Section 7.3 Soil

immn4BBB Erosion transports weathered materials across Earth's surface until they are deposited.

• The processes of erosion and deposition have shaped Earth's landscape in many ways.

• Gravity is the driving force behind major agents of erosion.

• Agents of erosion include running water, waves, glaciers, wind, and living things.

MAHEES Soil forms slowly as a result of mechanical and chemical processes.

• Soil consists of weathered rock and humus.

• Soil is either residual or transported.

• A typical soil profile has O-horizon, A-horizon, B-horizon, and C-horizon.

• Five factors influence soil formation: climate, topography, parent material, biological organisms, and time.

• Characteristics of soil include texture, fertility, and color.

Seieneqjr Vocabulary PuzzleMaker glencoe.com

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J Assessment

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^Vocabulary Review

^ Understand Key Concepts

Match the correct vocabulary term from the Study Guide to the following definitions.

1. the process of breaking down and changing rocks on or near Earth's surface

2. the removal of weathered materials from a location by water, wind, ice, or gravity

3. the fracturing of rock along curved lines that results when pressure is removed from bedrock

Each of the following sentences is false. Make each sentence true by replacing the italicized words with the correct vocabulary term from the Study Guide.

4. Weathering is caused by water flowing down the side of a slope.

5. The process by which eroded materials are left at a new location is called physical weathering.

6. Mechanical weathering is the process during which smaller eroded channels become deep and wide.

7. A soil horizon is formed from parent material that was moved away from its original source by water, wind, or a glacier.

8. A soil profile is a distinct layer or zone within a cross section of Earth's surface.

9. Humus is the loose covering of broken rock particles and decaying organic matter overlying the bedrock of Earth's surface.

Distinguish between the vocabulary terms in each pair.

10. weathering, erosion

11. chemical weathering, mechanical weathering

12. gully erosion, rill erosion

13. soil horizon, soil profile

14. erosion, deposition

15. residual soil, transported soil

Setone v Chapter Test glencoe.com

16. Approximately what percent of Earth's surface is presently covered by glaciers?

A. 5 percent

B. 10 percent

C. 20 percent

D. 50 percent

17. In which horizon is humus most concentrated?

A. A-horizon

B. B-horizon

C. C-horizon

D. O-horizon

18. Which is usually the primary factor that affects the rate of weathering?

A. topography

B. volume

C. climate

D. biological organisms

Use the figure below to answer Questions 19 and 20.

Factors Affecting Weathering Rate

19. Which process most likely produced the present appearance of this feature found in Arches National Park, Utah?

A. chemical weathering

B. mechanical weathering

C. earthquake activity

D. acid precipitation

20. Which erosional agent was most likely responsible for the appearance of this feature?

A. water

B. wind

C. glaciers

D. biological organisms

Chapter 7 • Assessment 187

Royalty-Free/CORBIS

Chapter J Assessment

21. Frost wedging primarily relies on which process(es)?

A. freezing and thawing

B. gravity

C. oxidation

D. depth

22. Which is not considered a factor of soil formation?

A. topography

B. parent material

C. time

D. chemistry

23. Which does not contribute to the rate of weathering?

A. rock type

B. rock composition

C. climate

D. fossils

Use the photo below to answer Questions 24 and 25.

Agents Mechanical Weathering Wind

24. Which agent of erosion is shown in the picture of Letchworth State Park, known as the Grand Canyon of the East, in central New York?

A. glaciers

B. wind

C. running water

D. earthquakes

25. Which is the underlying force behind the agent of erosion in Letchworth State Park?

A. pressure

B. gravity

C. temperature

D. light

188 Chapter 7 • Assessment

(l)Creatas/SuperStock, (r)Jim Reed/Photo Researchers, Inc.

26. Which describes a residual soil?

A. soil from sediment deposited by glaciers

B. sand that has collected in a floodplain

C. fine-grained sediment that was deposited by wind

D. layers of material that weathered from bedrock below

27. Which soil horizon is a zone of accumulation consisting of soluble minerals that have been carried by water from above?

A. A-horizon

B. B-horizon

C. C-horizon

D. O-horizon

28. A mature soil most likely possesses which characteristic?

A. thin B-horizons

B. thick B-horizons

C. fertility

D. dark color

Constructed Response

29. Analyze the relationship between surface area and rate of mechanical weathering of a rock.

30. Classify how different climates affect the way rocks weather.

Use the figure below to answer Question 31.

Use the figure below to answer Question 31.

Mechanical Weathering Colombia

31. Design a method that would have prevented the erosion occurring at this location.

Earth j.

flciMieqp rifi Chapter Test glencoe.com

32. List the factors that control the formation of soil, and give an example of the effects of each.

33. CAREERS IN EARTH SCIENCE A soil scientist stated that the soil in your area is acidic. Suggest a solution for the local gardeners.

Think Critically

34. Examine how the processes of erosion and deposition cause barrier islands to migrate.

Use the figure below to answer Question 35.

Gully Erosion Control Methods

35. Summarize how the processes of erosion and deposition have resulted in this landscape feature.

36. Create a poster that illustrates the effects of erosion and deposition in your community.

37. Draw and label a soil profile of a mature soil containing an O-horizon, A-horizon, B-horizon, C-horizon, and bedrock. Describe how each layer of the soil was developed.

Concept Mapping

38. Create a concept map using the following terms: weathering, erosion, deposition, chemical weathering, mechanical weathering, gully erosion, and rill erosion. Refer to the Skillbuilder Handbook for more information.

Challenge Question

39. Critique this statement: Weathering, erosion and deposition are all parts of the same process.

Chapter J Assessment

Additional Assessment

Mechanical Weathering Illustrations

40. Earth Science Imagine that you are a soil scientist studying a sample in the lab. Write a journal entry describing the soil sample. Include information about what you can infer from the soil sample.

Document-Based Questions

Data obtained from: United States Department of Agriculture, Natural Resources Conservation Service. Honeoye-New York State Soil, 2006.

Honeoye [HON ee yah] soils are exceptionally fertile soils that occur in New York. The word Honeoye is from the Iroquois Hay-e-a-yeah.

41. Using the photograph, create an illustration of the Honeoye soil and label the following layers: A-horizon, B-horizon, and C-horizon.

42. Describe the soil profile.

43. Is the soil pictured above undeveloped or mature? How can you tell?

Cumulative Review

44. What is the difference between latitude and longitude? (Chapter 2)

45. What is a mineral? (Chapter 4)

46. Which common chemical sedimentary rock consists of calcite? (Chapter 5)

Chapter Test glencoe.com

Chapter 7 • Assessment 189

(l)Annie Griffiths Belt/National Geographic Image Collection, (r)Dr. Ray Bryant, Will Hanna, Dr. John Galbralth USDA NRCS

Chapter 7 • Assessment 189

(l)Annie Griffiths Belt/National Geographic Image Collection, (r)Dr. Ray Bryant, Will Hanna, Dr. John Galbralth USDA NRCS

Standardized Test Practice

Multiple Choice

1. Which farming method is used to reduce wind erosion?

A. planting different crops

B. planting wind barriers

C. building earth mounds

D. building stone walls

Use the figure below to answer Questions 2-4.

2. Which image shows the erosional agent that was responsible for leaving behind U-shaped valleys, hanging valleys, lakes, and deposits of sediment in New England and New York State?

3. Which image shows the erosional agent responsible for dunes formed along the Gulf and Atlantic coasts of the United States?

4. What common factor is responsible for three of the four erosional processes pictured?

A. wind

B. heat

C. human intervention

D. gravity

5. What is the best-known feature of sedimentary rocks?

A. ripple marks

B. fossils

C. graded bedding

D. cross-bedding

6. How does granite differ from gabbro in coloring and silica content?

A. Granite is lighter colored with higher silica content.

B. Granite is darker colored with lower silica contents.

C. Granite is darker colored with higher silica contents.

D. Granite is lighter colored with lower silica contents.

7. Which is NOT an agent of chemical weathering?

A. water C. carbon dioxide

B. oxygen D. wind

Use the map below to answer Questions 8 and 9.

8. What can you infer about the location of the area shown in the road map?

A. It is largely uninhabited.

C. It is mostly impassable terrain.

D. It is a mountainous area.

9. Pikes Peak in Colorado is 4,300 m high. If a hiker wanted to climb an equivalent distance in the area located on this map, what two mountains should he climb?

A. Music Mountain and Mohon Peak

B. Music Mountain and Mount Tipton

C. Hualapai Peak and Mohon Peak

D. Mount Tipton and Mohon Peak

Earth

Topographic Maps Tipton

Earth

Short Answer

Use the graph below to answer Questions 10-12.

Line 1

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I Distance Traveled v. Time 1

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P Line 4

Line 2 Line 3

P Line 4

10. What was the average speed of the object represented by Line 1 during the 5 s its time was recorded?

11. Explain why Line 3 is horizontal.

12. What are the independent and dependent variables in this graph?

13. Describe how limestone forms.

14. Explain whether or not coal is a mineral.

15. When does regional metamorphism occur and what are its results?

Reading for Comprehension

Agricultural Land Use

Food production takes up almost half of Earth's land surface and threatens to consume the fertile land that still remains. The global impact of farming on the environment is revealed in new maps, which show that 40 percent of Earth's land is used for agriculture.

Navin Ramankutty, a land-use researcher with Wisconsin-Madison's Center for Sustainability and the Global Environment (SAGE), posed the following question: "How can we continue to produce food from the land while preventing negative environmental consequences, such as deforestation, water pollution, and soil erosion?" One potential solution could be "precision farming." This model uses new technology to improve productivity while reducing the use of water and the application of fertilizer and other potentially harmful chemicals. The precision system, currently being developed by NASA geoscientists, would use satellite data to help farmers decide how to use their resources with pinpoint accuracy based on the requirements of different areas of each field.

Article obtained from: Owen, J. Farming claims almost half of Earth's land, new maps show. National Geographic News. December 9, 2005.

16. According to this passage, which statement is false?

A. Farming can harm Earth.

B. Satellite data can improve farming.

C. Farming does not cause pollution.

D. "Precision farming" is a solution.

17. Which one is not a negative environmental consequence of farming listed in the passage?

A. deforestation

B. air pollution

C. water pollution

D. soil erosion

18. What can be inferred from this text?

A. There are solutions to improve farming and its effects on the land.

B. Wisconsin is the only state with farming problems.

C. People need to eat less so that less land is needed for food.

D. There is no fertile land left to cultivate.

NEED EXTRA HELP?

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Standardized Test Practice glencoe.com

Chapter 7 • Assessment 191

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Mass Movements, Wind, and Glaciers

Movements due to gravity, winds, and glaciers shape and change Earth's surface.

8.1 Mass Movements

H^Biaa Mass movements alter Earth's surface over time due to gravity moving sediment and rocks downslope.

8.2 Wind

IW<beh Wind modifies landscapes in all areas of the world by transporting sediment.

8.3 Glaciers

R^hbeh Glaciers modify landscapes by eroding and depositing rocks.

GeoFacts

More than 100,000 glaciers exist in Alaska, but ice covers only 5 percent of the state

Glaciers form when more snow falls in an area than melts in the same area.

Layers of snow on the glacier create pressure that changes the snow underneath to ice

Areas Significant Structural Geology

LAUNCH L

How does water affect sediments on slopes?

Water has a significant effect on sediments on slopes.

In this activity, you will demonstrate how the addition of water affects how sediments are held together.

Procedure t^

1. Read and complete the lab safety form.

2. Place 225 mL of sand in each of three separate containers, such as aluminum pie plates.

3. Add 20 mL of water to the first container of sand, and mix well. Add 100 mL of water to the second container of sand, and mix well. Add 200 mL of water to the third container of sand, and mix well.

4. Empty the three mixtures of sand and water onto a tray or piece of cardboard. Keep each mixture separate.

5. Test each mixture for its ability to be molded and retain its shape. Compare your results for the three samples.

Analysis

1. Describe how the addition of water affected the sand's ability to be molded in the three samples.

2. Explain why one mixture was better able to maintain its shape than the others.

3. Infer how water affects sediment on slopes.

External Processes that Shape Earth Make this Foldable to explain different processes that shape Earth's surface.

STEP 1 Fold the bottom of a horizontal sheet of paper up about 3 cm.

STEP 2 Fold in thirds.

STEP 3 Unfold and dot with glue or staple to make three pockets. Label as shown.

STEP 1 Fold the bottom of a horizontal sheet of paper up about 3 cm.

STEP 3 Unfold and dot with glue or staple to make three pockets. Label as shown.

IFfiMUIjl* Use this Foldable with Sections 8.1, 8.2, and 8.3. As you read, use index cards to summarize information in your own words and place them in the appropriate pockets.

Earth ^

Scienc^prilln

Visit glencoe.com to ^ study entire chapters online;

► explore h Mqjj^ animations:

• Interactive Time Lines

• Interactive Figures

• Interactive Tables

^ access Web Links for more information, projects, and activities;

► review content with the Interactive Tutor and take Self-Check Quizzes.

STEP 2 Fold in thirds.

Section 8.1

Objectives

I Analyze the relationship between gravity and mass movements. I Identify factors that affect mass movements. I Distinguish between types of mass movements. I Relate how mass movements affect people.

Review Vocabulary gravity: the force every object exerts on every other object due to their masses

New Vocabulary mass movement creep mudflow landslide slump avalanche

Mass Movements

N4TdHa Mass movements alter Earth's surface over time due to gravity moving sediment and rocks downslope.

Real-World Reading Link How fast can you travel on a waterslide? A number of factors might come into play, including the angle of the slide, the amount of water on the slide, the material of the slide, friction, and your own mass. These factors also affect mass movements on Earth's surface.

Mass Movements

How do landforms, such as mountains, hills, and plateaus, wear down and change? Landforms can change through processes involving wind, ice, and water, and sometimes through the force of gravity alone. The downslope movement of soil and weathered rock resulting from the force of gravity is called mass movement. Recall from Chapter 7 that weathering processes weaken and break rock into smaller pieces. Mass movements often carry the weathered debris downslope. Because climate has a major effect on the weathering activities that occur in a particular area, climatic conditions determine the extent of mass movement.

All mass movements, such as the one shown in Figure 8.1, occur on slopes. Because few places on Earth are completely flat, almost all of Earth's surface undergoes mass movement. Mass movements range from motions that are barely detectable to sudden slides, falls, and flows. The Earth materials that are moved range in size from fine-grained mud to large boulders.

^p Reading Check Describe how gravity causes a mass movement.

Figure 8.1 Mass movements can cause tree trunks to curve in order to continue growing opposite the pull of gravity, which is toward the center of Earth.

194 Chapter 8 • Mass Movements, Wind, and Glaciers

Dr. Marli Miller/Visuals Unlimited

Factors that Influence Mass Movements

Several factors influence the mass movements of Earth's material. One factor is the material's weight, which works to pull the material downslope. A second factor is the material's resistance to sliding or flowing, which depends on the amount of friction, how cohesive the material is, and whether it is anchored to the bedrock. A third factor is a trigger, such as an earthquake, that shakes material loose. Mass movement occurs when the forces pulling material downslope are stronger than the material's resistance to sliding, flowing, or falling.

Water is a fourth variable that influences mass movements. The landslide shown in Figure 8.2 occurred after days of heavy rains. Saturation by water greatly increases the weight of soils and sediments. In addition, as the water fills the tiny open spaces between grains, it acts as a lubricant between the grains, reducing the friction between them.

Types of Mass Movements

Mass movements are classified as creep, flows, slides, and rockfalls. Mass movements move different types of materials in various ways.

Creep The slow, steady, downhill flow of loose, weathered Earth materials, especially soils, is called creep. Because movement might be as little as a few centimeters per year, the effects of creep are usually noticeable only over long periods of time. One way to tell whether creep has occurred is to observe the positions of structures and objects. As illustrated in Figure 8.3, creep can cause once-vertical utility poles and fences to tilt, and trees and walls to break. Loose materials on almost all slopes undergo creep.

One type of creep that usually occurs in regions of permafrost, or permanently frozen soil, is called solifluction (SOH luh fluk shun). The material moved in solifluction is a mudlike liquid that is produced when water is released from melting permafrost during the warm season. The water saturates the surface layer of soil and is unable to move downward. As a result, the surface layer can slide slowly downslope.

Figure 8.2 Mass movements like the one shown here can significantly alter landscapes.

Summarize the factors that might have been involved in the mass movement.

Figure 8.2 Mass movements like the one shown here can significantly alter landscapes.

Summarize the factors that might have been involved in the mass movement.

Coastal Mass Movements Rock Falls

Section 1 • Mass Movements 195

(t)David McNew/Getty Images, (b)Ralph Lee Hopkins/Photo Researchers

Section 1 • Mass Movements 195

(t)David McNew/Getty Images, (b)Ralph Lee Hopkins/Photo Researchers

Lahar Armero

Figure 8.4 The city of Armero, in Colombia, was covered in mud and debris by a lahar that contained snowmelt and volcanic material.

Describe the effect of the lahar on the city shown above.

Figure 8.4 The city of Armero, in Colombia, was covered in mud and debris by a lahar that contained snowmelt and volcanic material.

Describe the effect of the lahar on the city shown above.

Figure 8.5 Mudflows can be extremely destructive and can result in severe property damage, road closures, and power outages.

Figure 8.5 Mudflows can be extremely destructive and can result in severe property damage, road closures, and power outages.

Extension Geology

196 Chapter 8 • Mass Movements, Wind, and Glaciers

(t)Steve Raymer/National Geographic Image Collection, (b)Gene Blevins/LA Daily News/CORBIS

Flows In some mass movements, Earth materials flow as if they were a thick liquid. The materials might move as slowly as a few centimeters per year or as rapidly as hundreds of kilometers per hour. Earth flows are moderately slow movements of soils, whereas mudflows are swiftly moving mixtures of mud and water. Mudflows can be triggered by earthquakes or similar vibrations and are common in volcanic regions where the heat from a volcano melts snow on nearby slopes that have fine sediment and little vegetation. The meltwater fills the spaces between the small particles of sediment and allows them to slide readily over one another and move downslope.

A lahar (LAH har) is a type of mudflow that occurs after a volcanic eruption. Often a lahar results when a snow-topped volcanic mountain erupts and melts the snow on top of a mountain. The melted snow mixes with ash and flows downslope. Figure 8.4 shows how a lahar that originated from Nevado del Ruiz, one of the volcanic mountains in the Andes, devastated a town. The Nevado del Ruiz is 5389 m high and covered with 25 km2 of snow and ice, which melted when it erupted. Four hours after Nevado del Ruiz erupted, lahars had traveled more than 100 km downslope. As a result of these lahars, which occurred in 1985, approximately 23,000 people were killed, 5000 were injured, and 5000 homes were destroyed.

^ Reading Check Determine what triggers a lahar.

Mudflows are also common in sloped, semiarid regions that experience intense, short-lived rainstorms. The Los Angeles Basin in Southern California is an example of an area where mud-flows are common. In such areas, periods of drought and forest fires leave the slopes with little protective vegetation. When heavy rains eventually fall in these areas, they can cause massive, destructive mudflows because there is little vegetation to anchor the soil. Mudflows are especially destructive in areas where urban development has spread to the bases of mountainous areas. These mudflows can burry homes, as shown in Figure 8.5.

196 Chapter 8 • Mass Movements, Wind, and Glaciers

(t)Steve Raymer/National Geographic Image Collection, (b)Gene Blevins/LA Daily News/CORBIS

Mass Movement Slide

Slides A rapid, downslope movement of Earth materials that occurs when a relatively thin block of soil, rock, and debris separates from the underlying bedrock is called a landslide, shown in Figure 8.6. The material rapidly slides downslope as one block, with little internal mixing. A landslide mass eventually stops and becomes a pile of debris at the bottom of a slope, sometimes damming rivers and causing flooding. Landslides are common on steep slopes, especially when soils and weathered bedrock are fully saturated by water. This destructive form of mass movement causes damage costing almost 2 billion dollars and 25 to 50 associated deaths per year in the United States alone. You will explore the movement of a landslide in the GeoLab at the end of this chapter.

A rockslide is a type of landslide that occurs when a sheet of rock moves downhill on a sliding surface. During a rockslide, some blocks of rock are broken into smaller blocks as they move downslope, as shown in Figure 8.7. Often triggered by earthquakes, rockslides can move large amounts of material.

Rockslides Caused Abrasion

Figure 8.7 During this rockslide, blocks of rock were broken into smaller blocks as they moved downslope.

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Interactive Figure To see an animation of a rockslide, visit glencoe.com.

Figure 8.7 During this rockslide, blocks of rock were broken into smaller blocks as they moved downslope.

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Interactive Figure To see an animation of a rockslide, visit glencoe.com.

Section 1 • Mass Movements 197

(t)Handout/Malacanang/Reuters/CORBIS, (b)Lloyd Cluff/CORBIS

Rysunek Horror

Figure 8.8 Slumps leave distinct crescent-shaped scars on hillsides as the soil rotates downward.

Figure 8.8 Slumps leave distinct crescent-shaped scars on hillsides as the soil rotates downward.

Slumps When the mass of material in a landslide moves along a curved surface, a slump results. Material at the top of the slump moves downhill, and slightly inward, while the material at the bottom of the slump moves outward. Slumps can occur in areas that have thick soils on moderate-to-steep slopes. Sometimes, slumps occur along highways where the slopes of soils are extremely steep. Slumps are common after rains, when water reduces the frictional contact between grains of soil and acts as a lubricant between surface materials and underlying layers. The weight of the additional water pulls material downhill. As with other types of mass movement, slumps can be triggered by earthquakes. Slumps leave crescent-shaped scars on slopes, as shown in Figure 8.8.

Reading Check Describe what conditions can cause a slump.

Avalanches Landslides that occur in mountainous areas with thick accumulations of snow are called avalanches. About 10,000 avalanches occur each year in the mountains of the western United States. Radiation from the Sun can melt surface snow, which then refreezes at night into an icy crust. Snow that falls on top of this crust can eventually build up, become heavy, slip off, and slide downslope as an avalanche. Avalanches can happen in early winter when snow accumulates on the warm ground. The snow in contact with the warm ground melts, then refreezes into a layer of jagged, slippery snow crystals.

Avalanches of dangerous size, like the one shown in Figure 8.9, occur on slope angles between 30° and 45°. When the angle of a slope is greater than 45°, enough snow cannot accumulate to create a large avalanche. At angles less than 30°, the slope is not steep enough for snow to begin sliding. A vibrating trigger, even from a single skier, can send this unstable layer sliding down a mountainside. Avalanches pose significant risks in places such as Switzerland, where more than 50 percent of the population lives in avalanche terrain.

Figure 8.9 Vibrations from a single skier can trigger an avalanche. Identify the conditions that make a landscape more vulnerable to avalanches.

Mass Movement Avalanche

198 Chapter 8 • Mass Movements, Wind, and Glaciers

(t)Dr. Marli Miller/Visuals Unlimited, (b)Mauritius/SuperStock

Figure 8.10 This rockfall in Topanga Canyon, California, was unusual in that it involved mainly one large rock.

Rockfalls On high cliffs, rocks are loosened by physical weathering processes, such as freezing and thawing, and by plant growth. As rocks break up and fall directly downward, they can bounce and roll, ultimately producing a cone-shaped pile of coarse debris, called talus, at the base of the slope. Rockfalls, such as the one shown in Figure 8.10, commonly occur at high elevations, in steep road cuts, and on rocky shorelines. Rockfalls are less likely to occur in humid regions where the rock is typically covered by a thick layer of soil, vegetation, and loose materials. On human-made rock walls, such as road cuts, rockfalls are particularly common.

Mass Movements Affect People

^ While mass movements are natural processes, human activities : often contribute to the factors that cause mass movements. Activities such as the construction of buildings, roads, and other structures can make slopes unstable. In addition, poor maintenance of septic systems, which often leak, can trigger slides. In the Philippines, mudslides, shown in Figure 8.11, were triggered after ten days of torrential rains delivered 200 cm of precipitation. A village estimated to have 3000 residents was totally destroyed.

Topanga Canyon Fossils

Figure 8.10 This rockfall in Topanga Canyon, California, was unusual in that it involved mainly one large rock.

Steel Nets Prevet Rock SlidesYann Arthus Bertrand Corbis
Figure 8.11 The mudflow on the island of Luzon occurred after days of rain.

Section 1 • Mass Movements 199

(t)Ted Soqui/CORBIS, (b)Yann Arthus-Bertrand/CORBIS

Yann Arthus Bertrand CorbisYann Arthus Bertrand Corbis
Figure 8.12 Covering hillsides with steel nets can reduce risks of mass movements and harm to humans. Identify the type of mass movement that these steel nets help prevent.

Reducing the risks Catastrophic mass move- f ments are most common on slopes greater than 25° als An that experience annual rainfall of over 90 cm. Risk | increases if that rainfall tends to occur in a short 1 period of time. Humans can minimize the destruc- chael tion caused by mass movements by not building Mi structures on or near the base of steep and unstable slopes.

Although preventing mass-movement disasters is not easy, some actions can help reduce the risks. For example, a series of trenches can be dug to divert running water around a slope and control its drainage. Landslides can be controlled by covering steep slopes with materials such as steel nets, shown in Figure 8.12, and constructing fences along highways in areas where rockslides are common. Other approaches involve the installation of retaining walls to support the bases of weakened slopes and prevent them from falling. Most of these efforts at slope stabilization and mass-movement prevention are only temporarily successful.

The best way to reduce the number of disasters related to mass movements is to educate people about the problems of building on steep slopes. For example, The United States Geological Survey (USGS) collects data about landslides in an effort to learn more about where and when landslides will occur. This information helps people decide where they can safely build homes or businesses. ^

Section 8.1 Assessment

Section Summary

I Mass movements are classified in part by how rapidly they occur.

I Factors involved in the mass movement of Earth materials include the material's weight, its resistance to sliding, the trigger, and the presence of water.

I Mass movements are natural processes that can affect human life and activities.

I Human activities can increase the potential for the occurrence of mass movements.

Understand Main Ideas

1. imandfffll Organize the following types of mass movements in order of increasing speed: slides, creep, flows, and rockfalls.

2. Identify the underlying force behind all forms of mass movement.

3. Analyze how water affects mass movements by using two examples of mass movement.

4. Appraise the effects of one type of mass movement on humans.

Think Critically

5. Generalize in which regions of the world mudflows are more common.

6. Evaluate how one particular human activity can increase the risk of mass movement and suggest a solution to the problem.

CZHZEZ^Earth Science

7. Make a poster that compares and contrasts solifluction and a slump. Consider the way soil moves and the role of water.

Solutions Wind Eroison
Figure 8.13 Wind erosion does not affect all areas of the United States equally. Observe which areas are subject to wind erosion.

Wind

N4TTHa Wind modifies landscapes in all areas of the world by transporting sediment.

Real-World Reading Link If you have ever been on a beach on a windy day, you might have felt the stinging of sand on your face. Sand travels in the wind if the wind is fast enough.

Wind Erosion and Transport

A current of rapidly moving air can pick up and carry sediment in the same way that water does. However, except for the extreme winds of hurricanes, tornadoes, and other strong storms, winds cannot generally carry particles as large as those transported by moving water. Regardless, wind is a powerful agent of erosion.

Winds transport materials by causing their particles to move in different ways. For example, wind can move sand on the ground in a rolling motion. A method of transport by which strong winds cause small particles to stay airborne for long distances is called suspension. Another method of wind transport, called saltation, causes a bouncing motion of larger particles. Saltation accounts for most sand transport by wind. Limited precipitation leads to an increase in the amount of wind erosion because precipitation holds down sediments and allows plants to grow. Thus, wind transport and erosion primarily occur in areas with little vegetative cover, such as deserts, semiarid areas, seashores, and some lakeshores. Wind erosion is a problem in many parts of the United States, as shown in Figure 8.13.

Wind Erosion in the United States

Wind Erosion in the United States

Wind Erosion Climate Factor Map
Areas of wind erosion

Figure 8.14 Through deflation, the wind can create a bowl-shaped blowout.

Figure 8.14 Through deflation, the wind can create a bowl-shaped blowout.

Blowouts Deflation Basins

Deflation The lowering of the land surface that results from the wind's removal of surface particles is called deflation. During the 1930s, portions of the Great Plains region, which stretches from Montana to Texas, experienced severe drought. The area was already suffering from the effects of poor agricultural practices, in which large areas of natural vegetation were removed to clear the land for farming. Strong winds readily picked up the dry surface particles, which lacked any protective vegetation. Severe dust storms resulted in daytime skies that were often darkened, and the region became known as the Dust Bowl.

Today, the Great Plains are characterized by thousands of shallow depressions known as deflation blowouts. Many are the result of the removal of surface sediment by wind erosion during the 1930s. The depressions range in size from a few meters to hundreds of meters in diameter. Deflation blowouts are also found in other areas that have sandy soil, as shown in Figure 8.14. Wind erosion continues today throughout the world, as shown by the sandstorm in Figure 8.15. ^p Reading Check Explain how deflation removes surface particles.

Figure 8.15 A sandstorm in a desert

region fills the air with dust.

V - J

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202 Chapter 8 • Mass Movements, Wind, and Glaciers

(t)Jerome Wyckoff/Animals Animals, (b)Remi Benali/CORBIS

202 Chapter 8 • Mass Movements, Wind, and Glaciers

(t)Jerome Wyckoff/Animals Animals, (b)Remi Benali/CORBIS

Deflation is a major problem in many agricultural areas of the world as well as in deserts, where wind has been consistently strong for thousands of years. In areas of intense wind erosion, coarse gravel and pebbles are usually left behind as the finer surface material is removed by winds. The coarse surface left behind is called desert pavement.

Abrasion Another process of erosion, called abrasion, occurs when particles such as sand rub against the surface of rocks or other materials. Abrasion occurs as part of the erosional activities of winds, streams, and glaciers. In wind abrasion, wind picks up materials such as sand particles and blows them against anything in their path. Because sand is often made of quartz, a hard mineral, wind abrasion can be an effective agent of erosion—windblown sand particles eventually wear away rocks. Structures, such as telephone poles, can also be worn away or undermined by wind abrasion, and paint and glass on homes and vehicles can be damaged by windblown sand.

Materials that are exposed to wind abrasion show unique characteristics. For example, windblown sand causes rocks to become pitted and grooved. With continued abrasion, rocks become polished on the windward side and develop smooth surfaces with sharp edges. In areas of shifting winds, abrasion patterns correspond to wind shifts, and different sides of rocks become polished and smooth. Rocks shaped by windblown sediments, such as those shown in Figure 8.16, are called ventifacts. Ventifacts are found in various shapes and sizes, and include arches and pillars.

^p Reading Check Identify the unique characteristics of materials shaped by abrasion.

Figure 8.16 Ventifacts form in different types of environments but most commonly in arid climates where wind can be a dominant erosional force.

Figure 8.16 Ventifacts form in different types of environments but most commonly in arid climates where wind can be a dominant erosional force.

Ventifacts Arch

(l)Robert Barber/Visuals Unlimited, (r)David Nunuk/Photo Researchers

(l)Robert Barber/Visuals Unlimited, (r)David Nunuk/Photo Researchers

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Responses

  • David
    What horizon is humus most concentrated?
    8 years ago
  • ellan
    Why can a heavy rain shower cause a large amount of erosion in a desert area?
    8 years ago
  • piia-noora
    What is the fracturing of rock along curved lines that result when pressure is removed from bedrock?
    8 years ago
  • samsa
    What is the underlying force behind the agent of erosion in letchworth, state park?
    8 years ago
  • merimac
    What agent oferosion os shown in the pictureof letchworth state park?
    8 years ago
  • Dina
    How does water affect mass movement glencoe?
    8 years ago
  • James
    What is the fracturing of rock along curved lines that results when pressure is removed from bedrock?
    8 years ago
  • Rebecca
    How to draw an avalanche?
    8 years ago
  • seren boyle
    Which is the underlying force behind the agent of erosion in letchwood state park?
    8 years ago
  • Diana
    Which erosional agent is responsible for colorado?
    8 years ago
  • markus
    What is the agent of erosion that is most likely acting on the surface?
    8 years ago
  • Pupa
    Is the soil in cny residual or transported?
    8 years ago
  • Shukornia Eyob
    Which erosional agent was most likely responsible for the feature found in arches?
    8 years ago
  • Ronald Villanueva
    How does mechanical weathering affect sandstorms in an arid climate?
    8 years ago
  • ramiro
    Which picture shows the erosional agent that was responsible for leaving behind?
    8 years ago
  • dimitri giordano
    What is the fracturing of rocks along curved lines that results when pressure is removed?
    7 years ago
  • thorsten
    How to draw chemical weathering?
    7 years ago
  • layton
    Which agent of erosion is shown in the picture of Letchworth State Park, known as the Grand Canyon?
    5 years ago
  • rowan
    How can mass movement affect people?
    4 months ago

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