Chapter 8: Mass Movements, Wind, and Glaciers EARTH SCIENCE Geology, the Environment and the...

Chapter 8: Mass Movements, Wind, and Glaciers

Chapter 8: Mass Movements, Wind, and Glaciers

EARTH SCIENCEGeology, the Environment and the Universe

Section 8.1 Mass Movements

Section 8.2 Wind

Section 8.3 Glaciers

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CHAPTER

8 Table Of Contents

Essential Questions

• What is the relationship between gravity and mass movements?

• What factors affect mass movements?

• What are the different types of mass movements and how are they described?

• How do mass movements affect people?

SECTION8.1

Mass Movements

Review Vocabulary• gravity: the force every object exerts on every

other object due to their masses

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

SECTION8.1

Mass Movements

New Vocabulary

mass movement

creep

mudflow

landslide

slump

avalanche

SECTION8.1

Mass Movements

Mass Movements• The downslope movement of soil and weathered

rock resulting from the force of gravity is called mass movement.

• Because climate has a major effect on the weathering activities that occur in a particular area, climatic conditions determine the extent of mass movement.

SECTION8.1

Mass Movements

Mass Movements• All mass movements occur on slopes. Because

few places on Earth are completely flat, almost all of Earth’s surface undergoes some degree of mass movement.

SECTION8.1

Mass Movements

Factors that Influence Mass Movements• Several factors influence the mass movements of

Earth’s material: the material’s weight, the material’s resistance to sliding or flowing, triggers that shake material loose, and the presence of water.

SECTION8.1

Mass Movements

• The slow, steady, downhill flow of loose, weathered Earth materials, especially soils, is called creep.

• The effects of creep are usually noticeable only over long periods of time.

Types of Mass MovementsCreep

SECTION8.1

Mass Movements

• One way to way to tell whether creep has occurred is to observe the positions of structures and objects.

Types of Mass MovementsCreep

SECTION8.1

Mass Movements

Types of Mass MovementsFlows

• Earth flows are moderately slow movements of soils, whereas mudflows are swiftly moving mixtures of mud and water.

SECTION8.1

Mass Movements

Types of Mass Movements Mudflows

SECTION8.1

Mass Movements

Types of Mass Movements Mudflows

SECTION8.1

Mass Movements

Types of Mass Movements Mudflows

SECTION8.1

Mass Movements

Types of Mass MovementsFlows

• Mudflows are also common in sloped, semi-arid regions that experience intense, short-lived rainstorms.

SECTION8.1

Mass Movements

Types of Mass MovementsFlows

• Mudflows can be triggered by earthquakes or similar vibrations.

• Lahars are mudflows that occur in volcanic regions where the heat from a volcano melts snow on nearby slopes that have fine sediment and little vegetation.

SECTION8.1

Mass Movements

Types of Mass Movements Lahar - Flows

SECTION8.1

Mass Movements

Types of Mass Movements Lahar - Flows

SECTION8.1

Mass Movements

Types of Mass Movements Lahar - Flows

SECTION8.1

Mass Movements

Types of Mass Movements Lahar - Flows

SECTION8.1

Mass Movements

Types of Mass MovementsSlides

• 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.

SECTION8.1

Mass Movements

Types of Mass MovementsSlides

• Landslides are common on steep slopes, especially when soils and weathered bedrock are fully saturated by water.

• A rockslide is a type of landslide that occurs when a sheet of rock moves downhill on a sliding surface. Rockslides are often triggered by earthquakes.

SECTION8.1

Mass Movements

Types of Mass Movements

Slides

• Landslides

SECTION8.1

Mass Movements

Types of Mass Movements

Slides

• Landslides

SECTION8.1

Mass Movements

Types of Mass Movements

Slides

• rockslides

SECTION8.1

Mass Movements

Types of Mass Movements

Slides

• rockslides

SECTION8.1

Mass Movements

Types of Mass MovementsSlides

• 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.

SECTION8.1

Mass Movements

Please click the image above to view the video.

SECTION8.1

Mass Movements

SECTION8.1

Mass Movements

slump

Stop here

Types of Mass MovementsSlides

• Landslides that occur in mountainous areas with thick accumulations of snow are called avalanches.

• Avalanches occur when snow that falls on an icy crust builds up, becomes heavy, slips off, and slides downslope.

SECTION8.1

Mass Movements

Types of Mass MovementsRockfalls

• On high cliffs, rocks that are loosened by physical weathering processes or by plant growth can break up and fall directly downward. Rockfalls commonly occur at high elevations, in steep road cuts, and on rocky shorelines.

SECTION8.1

Mass Movements

Mass Movements Affect People

• Human activities such as construction of buildings, roads, and other structures can make slopes unstable, contributing to the factors that cause mass movements.

SECTION8.1

Mass Movements

Mass Movements Affect PeopleReducing the risks

• 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.

SECTION8.1

Mass Movements

By adhering to sediment grains and rock layers, water reduces the risk of landslides.

a. true

b. false

SECTION8.1

Section Check

The effects of gravity increase with the steepness of the slope.

a. true

b. false

SECTION8.1

Section Check

In which type of mass movement does a section of rock or sediment move downhill along a curved surface?

a. rockslide

b. rockfall

c. slump

d. mudflow

SECTION8.1

Section Check

Essential Questions

• What are the conditions that contribute to the likelihood that an area will experience wind erosion ?

• What features are characteristic of wind erosion and deposition ?

• How do dunes form and migrate ?

SECTION8.2

Wind

• velocity: the speed of an object and its direction of motion

Review Vocabulary

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

SECTION8.2

Wind

New Vocabulary

deflation

abrasion

ventifact

dune

loess

SECTION8.2

Wind

Wind Erosion and Transport• Limited precipitation leads to an increase in the

amount of wind erosion because precipitation holds down sediments and allows plants to grow.

SECTION8.2

Wind

Wind Erosion and Transport

• Wind transport and erosion primarily occur in areas with little vegetative cover, such as deserts, semiarid areas, seashores, and some lakeshores.

SECTION8.2

Wind

Wind Erosion and Transport

• The lowering of the land surface that results from the wind’s removal of surface particles is called deflation.

Deflation

SECTION8.2

Wind

Wind Erosion and Transport

• During the 1930s, portions of the Great Plains region experienced severe drought. Because large areas of natural vegetation had been removed, strong winds readily picked up the dry surface particles. The region became known as the Dust Bowl.

Deflation

SECTION8.2

Wind

Wind Erosion and Transport

• Another process of erosion, called abrasion, occurs when particles such as sand rub against the surface of rocks or other materials.

Abrasion

SECTION8.2

Wind

Wind Erosion and Transport

• 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.

Abrasion

SECTION8.2

Wind

Wind Erosion and Transport

• Rocks shaped by windblown sediments are called ventifacts.

Abrasion

SECTION8.2

Wind

• In windblown environments, sand particles tend to accumulate where an object, such as a rock, landform, or piece of vegetation, blocks the forward movement of the particles. Over time, the pile of windblown sand develops into a dune.

Dunes

Wind Deposition

SECTION8.2

Wind

Wind Deposition

• The conditions under which a dune forms determine its shape and include the availability of sand, wind velocity, wind direction, and the amount of vegetation present.

Dunes

SECTION8.2

Wind

Wind Deposition

• Dune migration is caused when prevailing winds continue to move sand from the windward side of a dune to its leeward side, causing the dune to move slowly over time.

Dunes

SECTION8.2

Wind

Please click the image above to view the interactive table.

SECTION8.2

Wind

Wind Deposition

• Thick, windblown silt deposits are known as loess.

• Loess soils are some of the most fertile soils because they contain abundant minerals and nutrients.

Loess

SECTION8.2

Wind

• This map shows the location of loess deposits in the continental United States.

Wind DepositionLoess

SECTION8.2

Wind

Most of the sand that is blown by wind moves along the ground with a bouncing motion.

a. true

b. false

SECTION8.2

Section Check

Which feature forms as a result of deflation?

a. dunes

b. blowouts

c. ventifacts

d. pillars

SECTION8.2

Section Check

How do sand dunes migrate? Possible answer: Sand that is blown by wind from the windward side of the dune accumulates at the crest until it is carried down the leeward side. As long as the wind blows, this process continues, moving sand from one side of the dune to the other and causing the dune to advance.

SECTION8.2

Section Check

Essential Questions• How do glaciers form?

• What are the similarities and differences between valley glaciers and continental glaciers?

• How do glaciers modify landscapes?

• What features are characteristic of glacial erosion and deposition?

SECTION8.3

Glaciers

• latitude: distance in degrees north and south of the equator

Review Vocabulary

• Glaciers modify landscapes by eroding and depositing rocks.

SECTION8.3

Glaciers

New Vocabulary

glacier

valley glacier

continental glacier

cirque

moraine

outwash plain

drumlin

esker

kame

kettle

SECTION8.3

Glaciers

Moving Masses of Ice• A large mass of

moving ice is called a glacier.

• Glaciers form near Earth’s poles and in mountainous areas at high elevations. They cover about 10 percent of Earth’s surface.

SECTION8.3

Glaciers

Moving Masses of Ice

• Glaciers that form in valleys in high, mountainous areas are called valley glaciers.

• As valley glaciers flow downslope, they carve V-shaped stream valleys into U-shaped glacial valleys.

Valley glaciers

SECTION8.3

Glaciers

Valley Glaciers

 Bylot Island, Canada

Moving Masses of Ice

• Glaciers that cover broad, continent-sized areas are called continental glaciers.

• These glaciers form in cold climates where snow accumulates over many years.

Continental glaciers

SECTION8.3

Glaciers

Moving Masses of IceGlacial movement

• Both valley glaciers and continental glaciers move outward when snow gathers at the zone of accumulation, a location in which more snow falls than melts, evaporates, or sublimates.

SECTION8.3

Glaciers

• Of all the erosional agents, glaciers are the most powerful because of their great size and weight.

Glacial Erosion

SECTION8.3

Glaciers

• When a valley glacier moves, it breaks off pieces of rock through a process called plucking.

• When glaciers with embedded rocks move over bedrock, they act like grains on a piece of sandpaper, grinding parallel scratches into the bedrock.

Glacial Erosion

SECTION8.3

Glaciers

• At the high elevations where snow accumulates, valley glaciers scoop out deep, bowl-shaped depressions, called cirques.

Glacial Erosion

SECTION8.3

Glaciers

• When there are glaciers on three or more sides of a mountaintop, the carving action creates a steep, pyramid-shaped peak, called a horn.

Glacial Erosion

SECTION8.3

Glaciers

Glacial Erosion

• Hanging valleys are formed by valley glaciers when higher tributary glaciers converge with the lower primary glaciers and later retreat. A valley is left hanging high above the primary valley floor.

SECTION8.3

Glaciers

Glacial Deposition• Glacial till is the unsorted rock, gravel, sand, and

clay that glaciers carry embedded in their ice and on their tops, sides, and front edges.

• Glaciers deposit unsorted ridges of till called moraines when the glacier retreats.

SECTION8.3

Glaciers

Glacial DepositionOutwash

• When the farthest ends of a glacier melt, meltwater floods the valley below. Outwash is the gravel, sand, and fine silt sediment that is deposited by meltwater carried away from the glacier.

SECTION8.3

Glaciers

Glacial DepositionOutwash

• The area at the leading edge of a glacier where meltwater flows and deposits outwash is called an outwash plain.

SECTION8.3

Glaciers

Glacial DepositionDrumlins, eskers, and kames

• Continental glaciers that move over older moraines form the material into elongated landforms called drumlins.

SECTION8.3

Glaciers

Glacial DepositionDrumlins, eskers, and kames

• Streams flowing under melting glaciers leave long, winding ridges of layered sediments called eskers.

• A kame is a mound of layered sediment that forms when till gets washed into depressions or openings in the melting ice.

SECTION8.3

Glaciers

Visualizing Continental Glacial Features

• Continental glaciers carve out vast regions of landscape, leaving behind distinctive features such as kames, eskers, drumlins, and moraines.

SECTION8.3

Glaciers

SECTION8.3

Glaciers

Please click the image above to view the video.

Glacial Deposition

• Kettles, or kettle lakes, form when water from runoff or precipitation fills a hole that formed when a large block of ice broke off a continental glacier and melted.

Glacial lakes

SECTION8.3

Glaciers

Glacial Deposition

• With valley glaciers, cirques can also fill with water and become cirque lakes.

• When a terminal moraine blocks off a valley, the valley fills with water to form a moraine-dammed lake.

Glacial lakes

SECTION8.3

Glaciers

About how much of Earth’s surface is currently covered by glaciers ?

a. 10 percent

b. 20 percent

c. 30 percent

d. 40 percent

SECTION8.3

Section Check

Which glacial feature forms from sediments deposited by a stream flowing beneath a glacier?

a. esker

b. cirque

c. kettle

d. moraine

SECTION8.3

Section Check

Which glacial feature forms as a result of deposition of sediment?

a. horn

b. arête

c. cirque

d. moraine

SECTION8.3

Section Check

CHAPTER

8 Mass Movements, Wind, and Glaciers

Resources

Chapter Assessment Questions

Standardized Test Practice

Click on a hyperlink to view the corresponding feature.

Study Guide

Earth Science Online

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

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

SECTION8.1

Mass Movements

Study Guide

• 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.

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

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

SECTION8.1

Mass Movements

Study Guide

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

• Wind is a powerful agent of erosion.

• Wind can transport sediment in several ways, including suspension and saltation.

SECTION8.2

Wind

Study Guide

• Dunes form when wind velocity slows down and windblown sand is deposited.

• Dunes migrate as long as winds continue to blow.

SECTION8.2

Wind

Study Guide

• Glaciers modify landscapes by eroding and depositing rocks.

• Glaciers are large moving masses of ice that form near Earth’s poles and in mountain areas.

• Glaciers can be classified as valley glaciers or continental glaciers.

SECTION8.3

Glaciers

Study Guide

• Glaciers modify the landscape by erosion and deposition.

• Features formed by glaciers include U-shaped valleys, hanging valleys, moraines, drumlins, and kettles.

SECTION8.3

Glaciers

Study Guide

Which sediment grain size is most abundant in loess?

a. clay

b. silt

c. sand

d. gravel

CHAPTER

8 Mass Movements, Wind, and Glaciers

Chapter Assessment

Which observation provides evidence that material has moved by the process of creep?

a. scattered large boulders

b. steep scarps in hills

c. tilted trees or posts

d. piles of rock talus

CHAPTER

8 Mass Movements, Wind, and Glaciers

Chapter Assessment

By what agent is glacial outwash deposited?

a. ice

b. wind

c. water

d. gravity

CHAPTER

8 Mass Movements, Wind, and Glaciers

Chapter Assessment

What is a lahar?

Answer: A lahar is a mudflow that forms on a volcano, often just after an eruption. The presence of loose volcanic ash and snow that can melt rapidly contributes to conditions favorable for the formation of lahars.

CHAPTER

8 Mass Movements, Wind, and Glaciers

Chapter Assessment

How do valley glaciers and continental glaciers differ?

Possible answer: Valley glaciers form in mountains at high altitudes and are comparatively small. Continental glaciers are much larger and form at high latitudes. Continental glaciers have, however, extended into midlatitudes during ice ages.

CHAPTER

8 Mass Movements, Wind, and Glaciers

Chapter Assessment

Which landmass has the most glacier ice?

a. Greenland

b. North America

c. South America

d. Antarctica

CHAPTER

8 Mass Movements, Wind, and Glaciers

Standardized Test Practice

Which type of sand dune has a horseshoe shape with arms that point downwind?

a. transverse

b. barchan

c. parabolic

d. longitudinal

CHAPTER

8 Mass Movements, Wind, and Glaciers

Standardized Test Practice

By which process does a ventifact form?

a. abrasion by windblown sand

b. erosion of kame gravel

c. tumbling in a landslide

d. scraping beneath a glacier

CHAPTER

8 Mass Movements, Wind, and Glaciers

Standardized Test Practice

How does a kettle lake form?

Answer: As a glacier recedes, blocks of glacier ice are sometimes left in front of the receding ice margin. When an ice block melts, a depression remains. A kettle lake forms if the depression remains filled with water.

CHAPTER

8 Mass Movements, Wind, and Glaciers

Standardized Test Practice

Flows and slides are basic types of mass movements. How is a flow different from a slide?

Possible answer: A flow moves like a liquid. Some flows are stiff and move relatively slowly; others are thin and flow like water. A slide is a mass of rock or sediment that rapidly slides over a surface of weakness. The mass sometimes breaks apart as it moves downhill.

CHAPTER

8 Mass Movements, Wind, and Glaciers

Standardized Test Practice