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Erosional Forces
For Sale—Ocean ViewThis home, once perched on a hillside overlooking the water, hasbeen destroyed by landslides and flooding. In this chapter you willlearn how large amounts of soil, such as the soil that once sup-ported this house, can move from one place to another.
Name three major landforms around the world and explain whaterosional forces helped shape them.Science Journal
Erosion is a process thatwears away surface materi-als and moves them fromone place to another.
SECTION 1Erosion by GravityMain Idea Mass move-ment is a type of erosionthat happens as gravitymoves materials downslope.
SECTION 2GlaciersMain Idea As glaciers passover land, they erode it,changing features onEarth’s surface.
SECTION 3WindMain Idea When airmoves, it picks up loosematerial and transports it toother places.
Paul A. Souders/CORBIS
Erosion and Deposition Makethe following Foldable to helpyou identify the examples oferosion and deposition.
Fold one piece ofpaper widthwiseinto thirds.
Fold the paper lengthwise into fourths.
Unfold, lay thepaper lengthwise,and draw linesalong the folds.
Label your tableas shown.
Make a Table As you read the chapter, com-plete the table, listing specific examples of ero-sion and deposition for each erosional force.
STEP 4
STEP 3
STEP 2
STEP 1
1. Place a small pile of a sand-and-gravelmixture into a large shoe-box lid.
2. Move the sediment pile to the other endof the lid without touching the particleswith your hands. You can touch andmanipulate the box lid.
3. Try to move the mixture in a number ofdifferent ways.
4. Think Critically In your Science Journal,describe the methods you used to movethe sediment. Which method was mosteffective? Explain how your methodscompare with forces of nature that movesediment.
Demonstrate Sediment MovementCan you think of ways to move somethingwithout touching it? In nature, sediment ismoved from one location to another by avariety of forces. What are some of theseforces? In this lab, you will investigate tofind out the answers to these questions.
WARNING: Do not pour sand or gravel downthe drain.
Start-Up Activities
Preview this chapter’scontent and activities at earth.msscience.com
209
ErosionalForce
Erosion Deposition
Gravity
Glaciers
Wind
Paul A. Souders/CORBIS
210 A CHAPTER 8 Erosional Forces
Apply It! As you read thechapter, be aware of causes and effects ofgravity and ice. Find five causes and theireffects.
Learn It! A cause is the reason something happens. Theresult of what happens is called an effect. Learning to identify causes andeffects helps you understand why things happen. By using graphic organiz-ers, you can sort and analyze causes and effects as you read.
Practice It! Read the following paragraph. Then use thegraphic organizer below to show what happened when ice freezes in thecracks of rocks.
…Rockfalls happen when blocks of rock break loosefrom a steep slope and tumble through the air. Asthey fall, these rocks crash into other rocks andknock them loose. More and more rocks break looseand tumble to the bottom. The fall of a single, largerock down a steep slope can cause serious damage tostructures at the bottom. During the winter, when icefreezes in the cracks of rocks, the cracks expand andextend. In the spring, the pieces of rock break looseand fall down the mountainside…
—from page 212
Cause
Effect Effect Effect
210 B
Graphic organizers such as the
Cause-Effect organizer help
you organize what you are
reading so you can remember
it later.
Use this to focus on the main ideas as you read the chapter.
Before you read the chapter, respond to the statements
below on your worksheet or on a numbered sheet of paper.
• Write an A if you agree with the statement.
• Write a D if you disagree with the statement.
After you read the chapter, look back to this page to see if you’ve
changed your mind about any of the statements.
• If any of your answers changed, explain why.
• Change any false statements into true statements.
• Use your revised statements as a study guide.
Before You Read Statement After You ReadA or D A or D
1 Gravity, water, wind, and glaciers are commonagents of erosion.
2 Deposition occurs when agents of erosion loseenergy and drop the sediments they are carrying.
3 Mass movement is the slow process of changingrock into soil.
4 The two broad categories of glaciers are calledcontinental glaciers and valley glaciers.
5 During the most recent ice age, continental gla-ciers covered the entire Earth.
6 Valley glaciers carve deep, V-shaped valleys.
7 Abrasion can be caused by windblown sedimentstriking and wearing away the surface of rock.
8 Most dunes move, or migrate away from thedirection of the wind.
9 During sandstorms, large sand grains are oftencarried high into the atmosphere.
Print out a worksheetof this page at earth.msscience.com
210 CHAPTER 8 Erosional Forces
Erosion and DepositionDo you live in an area where landslides occur? As Figure 1
shows, large piles of sediment and rock can move downhill withdevastating results. Such events often are triggered by heavy rain-fall. The muddy debris at the lower end of the slide comes frommaterial that once was further up the hillside. The displaced soiland rock debris is a product of erosion (ih ROH zhun). Erosionis a process that wears away surface materials and moves themfrom one place to another.
What wears away sediments? How were you able tomove the pile of sediments in the Launch Lab? If you happenedto tilt the pan, you took advantage of an important erosionalforce—gravity. Gravity is the force of attraction that pulls allobjects toward Earth’s center. Other causes of erosion, alsocalled agents of erosion, are water, wind, and glaciers.
Water and wind erode materials only when they haveenough energy of motion to do work. For example, air can’tmove much sediment on a calm day, but a strong wind canmove dust and even larger particles. Glacial erosion works dif-ferently by slowly moving sediment that is trapped in solid ice.As the ice melts, sediment is deposited, or dropped. Sometimessediment is carried farther by moving meltwater.
■ Explain the differences betweenerosion and deposition.
■ Compare and contrast slumps,creep, rockfalls, rock slides, andmudflows.
■ Explain why building on steepslopes might not be wise.
Many natural features throughoutthe world were shaped by erosion.
Review Vocabularysediment: loose materials, suchas mineral grains and rock frag-ments, that have been moved byerosional forces
New Vocabulary
• erosion
• deposition
• mass movement
• slump
• creep
Erosion by Gravity
Figure 1 The jumbled sedimentat the base of a landslide is mate-rial that once was located fartheruphill.Define the force that moves mate-rials toward the center of Earth.
Robert L. Schuster/USGS
Dropping Sediments Agents of erosion drop the sedimentsthey are carrying as they lose energy. This is called deposition.When sediments are eroded, they are not lost from Earth—theyare just relocated.
Mass MovementThe greater an object’s mass is, the greater its gravitational
force is. Earth has such a great mass that gravity is a major forceof erosion and deposition. Rocks and other materials, especiallyon steep slopes, are pulled toward the center of Earth by gravity.
A mass movement is any type of erosion that happens asgravity moves materials downslope. Some mass movements areso slow that you hardly notice they’re happening. Others happenquickly—possibly causing catastrophes. Common types of massmovement include slump, creep, rockfalls, rock slides, and mud-flows. Landslides are mass movements that can be one of thesetypes or a combination of these types of mass movement.
What is a mass movement?
Slump When a mass of material slips down along a curved sur-face, the mass movement is called slump. Often, when a slopebecomes too steep, the base material no longer can support therock and sediment above it. The soil and rock slip downslope asone large mass or break into several sections.
Sometimes a slump happens when water moves to the baseof a slipping mass of sediment. This water weakens the slippingmass and can cause movement of material downhill. Or, if astrong rock layer lies on top of a weaker layer—commonlyclay—the clay can weaken further under the weight of the rock.The clay no longer can support the strong rock on the hillside.As shown in Figure 2, a curved scar is left where the slumpedmaterials originally rested.
SECTION 1 Erosion by Gravity 211
Original position
Modeling SlumpProcedureWARNING: Do not pour labmaterials down the drain.1. Place one end of a baking
pan on two bricks andposition the other end overa sink with a sealed drain.
2. Fill the bottom half of thepan with gelatin powderand the top half of the panwith aquarium gravel.Place a large, flat rock onthe gravel.
3. Using a watering can,sprinkle water on thematerials in the pan forseveral minutes. Recordyour observations in yourScience Journal.
Analysis1. What happened to the
different sediments in thepan?
2. Explain how yourexperiment models slump.
Figure 2 Slump occurs whenmaterial slips downslope as onelarge mass.Infer What might have caused thisslump to happen?
Martin G. Miller/Visuals Unlimited
Creep The next time you travel, look alongthe roadway or trail for slopes where trees andfence posts lean downhill. Leaning trees andhuman-built structures show another massmovement called creep. Creep occurs whensediments slowly shift their positions downhill,as Figure 3 illustrates. Creep is common in areasof frequent freezing and thawing.
Rockfalls and Rock Slides Signs alongmountainous roadways warn of another type ofmass movement called rockfalls. Rockfalls hap-pen when blocks of rock break loose from asteep slope and tumble through the air. As theyfall, these rocks crash into other rocks and
knock them loose. More and more rocks break loose and tum-ble to the bottom. The fall of a single, large rock down a steepslope can cause serious damage to structures at the bottom.During the winter, when ice freezes in the cracks of rocks, thecracks expand and extend. In the spring, the pieces of rock breakloose and fall down the mountainside, as shown in Figure 4.
Rock slides occur when layers of rock—usually steep layers—slip downslope suddenly. Rock slides, like rockfalls, are fast andcan be destructive in populated areas. They commonly occur inmountainous areas or in areas with steep cliffs, also as shown inFigure 5. Rock slides happen most often after heavy rains or dur-ing earthquakes, but they can happen on any rocky slope at anytime without warning.
Figure 4 Rockfalls, such as thisone, occur as material free fallsthrough the air.
Figure 5 Rock slides are common inregions where layers of rock are steep.
212
Figure 3 Over time, creep hascaused these tree trunks to leandownhill. The trees then curvedback toward the Sun.
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Mudflows What would happen if you tooka long trip and forgot to turn off the sprinklerin your hillside garden before you left? If thesoil is usually dry, the sprinkler water couldchange your yard into a muddy mass of mate-rial much like chocolate pudding. Part of yourgarden might slide downhill. You would havemade a mudflow, a thick mixture of sedimentsand water flowing down a slope. The mudflowin Figure 6 caused a lot of destruction.
Mudflows usually occur in areas that havethick layers of loose sediments. They oftenhappen after vegetation has been removed byfire. When heavy rains fall on these areas,water mixes with sediment, causing it to become thick andpasty. Gravity causes this mass to flow downhill. When a mud-flow finally reaches the bottom of a slope, it loses its energy ofmotion and deposits all the sediment and everything else it hasbeen carrying. These deposits often form a mass that spreadsout in a fan shape. Why might mudflows cause more damagethan floodwaters?
What conditions are favorable for triggeringmudflows?
Mudflows, rock slides, rockfalls, creep, and slump are similarin some ways. They all are most likely to occur on steep slopes,and they all depend on gravity to make them happen. Also, alltypes of mass movement occur more often after a heavy rain.The water adds mass and creates fluid pressure between grainsand layers of sediment. This makes the sediment expand—pos-sibly weakening it.
Consequences of ErosionPeople like to have a great view and live in scenic areas away
from noise and traffic. To live this way, they might build or moveinto houses and apartments on the sides of hills and mountains.When you consider gravity as an agent of erosion, do you thinksteep slopes are safe places to live?
Building on Steep Slopes When people build homes onsteep slopes, they constantly must battle naturally occurringerosion. Sometimes builders or residents make a slope steeper orremove vegetation. This speeds up the erosion process and cre-ates additional problems. Some steep slopes are prone to slumpsbecause of weak sediment layers underneath.
Figure 6 Mudflows, such asthese in the town of Sarno, Italy,have enough energy to movealmost anything in their paths.Explain how mudflows differ fromslumps, creep, and rock slides.
SECTION 1 Erosion by Gravity 213
Driving Force The forcethat drives most types oferosion is gravity. Water atan elevation has potential,or stored energy. Whenwater drops in elevationthis energy changes tokinetic energy, or energyof motion. Water may thenbecome a powerful agentof erosion. Find out howwater has shaped theregion in which you live.
AP/Wide World Photos
214 CHAPTER 8 Erosional Forces
Self Check1. Define the term erosion and name the forces that cause it.
2. Explain how deposition changes the surface of Earth.
3. Describe the characteristics that all types of massmovements have in common.
4. Describe ways to help slow erosion on steep slopes.
5. Think Critically When people build houses androads, they often pile up dirt or cut into the sidesof hills. Predict how this might affect sediment ona slope. Explain how to control the effects of suchactivities.
SummaryErosion and Deposition
• Gravity is the force that pulls all objectstoward Earth’s center.
• Water and wind erode materials only whenthey have enough energy of motion to do work.
• Agents of erosion drop sediment as they loseenergy.
Mass Movement
• The greater an object’s mass is, the greaterits gravitational force is.
• Gravity is a major force of erosion anddeposition.
• Common types of mass movement includeslump, creep, rockfalls, rock slides, andmudflows.
6. Compare and Contrast What are the similarities anddifferences between rock falls and rock slides?
Making Steep Slopes Safe Plants can bebeautiful or weedlike—but they all have root struc-tures that hold soil in place. One of the best ways toreduce erosion is to plant vegetation. Deep treeroots and fibrous grass roots bind soil together,reducing the risk of mass movement. Plants alsoabsorb large amounts of water. Drainage pipes ortiles inserted into slopes can prevent water frombuilding up, too. These materials help increase thestability of a slope by allowing excess water to flowout of a hillside more easily.
Walls made of concrete or boulders also canreduce erosion by holding soil in place, as shown inFigure 7. However, preventing mass movementson a slope is difficult because rain or earthquakescan weaken all types of Earth materials, eventuallycausing them to move downhill.
What can be done to slowerosion on steep slopes?
People who live in areas with erosion problems spend a lot oftime and money trying to preserve their land. Sometimes they’resuccessful in slowing down erosion, but they never can eliminateerosion and the danger of mass movement. Eventually, gravitywins. Sediment moves from place to place, constantly reducingelevation and changing the shape of the land.
Figure 7 Some slopes are stabi-lized by building walls made fromconcrete or stone.
earth.msscience.com/self_check_quizMartin G. Miller/Visuals Unlimited
SECTION 2 Glaciers 215
How Glaciers Form and Move If you’ve ever gone sledding, snowboarding, or skiing, you
might have noticed that after awhile, the snow starts to packdown under your weight. A snowy hillside can become icy if it iswell traveled. In much the same way, glaciers form in regionswhere snow accumulates. Some areas of the world, as shown inFigure 8, are so cold that snow remains on the ground year-round. When snow doesn’t melt, it piles up. As it accumulatesslowly, the increasing weight of the snow becomes great enoughto compress the lower layers into ice. Eventually, there can beenough pressure on the ice so that it becomes plasticlike. Themass slowly begins to flow in a thick, plasticlike lower layer, andice slowly moves away from its source. A large mass of ice andsnow moving on land under its own weight is a glacier.
Ice Eroding Rock Glaciers are agents of erosion. As glaciers pass over land, they
erode it, changing features on the surface. Glaciers then carryeroded material along and deposit it somewhere else. Glacial ero-sion and deposition change large areas of Earth’s surface. How isit possible that something as fragile as snow or ice can push asidetrees, drag rocks along, and slowly change the surface of Earth?
Glaciers
■ Explain how glaciers move.■ Describe evidence of glacial
erosion and deposition.■ Compare and contrast till and
outwash.
Glacial erosion and deposition createmany landforms on Earth.
Review Vocabularyplasticlike: not completely solidor liquid; capable of beingmolded or changing form
New Vocabulary
• glacier • moraine
• plucking • outwash
• till
Figure 8 The white regionson this map show areas thatare glaciated today.Antarctica
Australia
Europe
Asia
Africa
South America
NorthAmerica
Greenland
216 CHAPTER 8 Erosional Forces
Plucking Glaciers weather and erodesolid rock. When glacial ice melts, waterflows into cracks in rocks. Later, the waterrefreezes in these cracks, expands, andfractures the rock. Pieces of rock then arelifted out by the ice, as shown in Figure 9.This process, called plucking, results inboulders, gravel, and sand being added tothe bottom and sides of a glacier.
What is plucking?
Transporting and Scouring As it moves forward overland, a glacier can transport huge volumes of sediment androck. Plucked rock fragments and sand at its base scour andscrape the soil and bedrock like sandpaper against wood, erod-ing the ground below even more. When bedrock is gougeddeeply by rock fragments being dragged along, marks such asthose in Figure 10 are left behind. These marks, called grooves,are deep, long, parallel scars on rocks. Shallower marks arecalled striations (stri AY shunz). Grooves and striations indicatethe direction in which the glacier moved.
Ice Depositing Sediment When glaciers begin to melt, they are unable to carry much
sediment. The sediment drops, or is deposited, on the land.When a glacier melts and begins to shrink back, it is said toretreat. As it retreats, a jumble of boulders, sand, clay, and silt isleft behind. This mixture of different-sized sediments is called
till. Till deposits can coverhuge areas of land. Thousandsof years ago, huge ice sheets inthe northern United States leftenough till behind to fill val-leys completely and make theseareas appear flat. Till areasinclude the wide swath ofwhat are now wheat farmsrunning northwestward fromIowa to northern Montana.Some farmland in parts of Ohio,Indiana, and Illinois and therocky pastures of New Englandare also regions that contain tilldeposits.
Figure 9 Plucking is a processthat occurs when a moving glacierpicks up loosened rock particles.
Figure 10 When glaciers melt,striations or grooves can be foundon the rocks beneath. These glacialgrooves on Kelley’s Island, Ohio,give evidence of past glacial ero-sion and movement.
The rock is being draggedalong by the glacier.
IceWater at a glacier's base flows into cracks and freezes. Pieces of rock are plucked by the ice.
James N. Westwater
Moraine Deposits Till also is deposited at the end ofa glacier when it is not moving forward. Unlike the tillthat is left behind as a sheet of sediment over the land,this type of deposit doesn’t cover such a wide area. Rocksand soil are moved to the end of the glacier, much likeitems on a grocery store conveyor belt. Because of this, abig ridge of material piles up that looks as though it hasbeen pushed along by a bulldozer. Such a ridge is called amoraine. Moraines also are deposited along the sides ofa glacier, as shown in Figure 11.
Outwash Deposits When glacial ice starts to melt,the meltwater can deposit sediment that is different fromtill. Material deposited by the meltwater from a glacier,most often beyond the end of the glacier, is called outwash.Meltwater carries sediments and deposits them in layers.Heavier sediments drop first, so bigger pieces of rock aredeposited closer to the glacier. The outwash from a glacier alsocan form into a fan-shaped deposit when the stream of melt-water deposits sand and gravel in front of the glacier.
What is outwash?
Eskers Another type of outwash deposit looks like a long,winding ridge. This deposit forms in a melting glacier whenmeltwater forms a river within the ice, as shown in the diagramin Figure 12. This river carries sand and gravel and depositsthem within its channel. When the glacier melts, a winding ridgeof sand and gravel, called an esker (ES kur), is left behind. Anesker is shown in the photograph in Figure 12.
Figure 11 Moraines are form-ing along the sides of this glacier.Unlike the moraines that format the ends of glaciers, thesemoraines form as rock and sedi-ment fall from nearby slopes.
Figure 12 Eskers are glacialdeposits formed by meltwater.
217
Ice
IceTunnel
Meltwaterstream
Eskers form when sedimentdeposited in ice tunnels orby streams on top of the ice isleft behind on Earth’s surface.
The snake-like shapeof this esker in NorthDakota is characteristic ofthis type of glacial deposit.
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218 CHAPTER 8 Erosional Forces
Continental GlaciersThe two types of glaciers are continental
glaciers and valley glaciers. Today, continen-tal glaciers, like the one in Figure 13 coverten percent of Earth, mostly near the poles inAntarctica and Greenland. These continentalglaciers are huge masses of ice and snow.Continental glaciers are thicker than somemountain ranges. Glaciers make it impos-sible to see most of the land features inAntarctica and Greenland.
In what regions on Earthwould you expect to findcontinental glaciers?
Climate Changes In the past, continental glaciers covered asmuch as 28 percent of Earth. Figure 14 shows how much ofNorth America was covered by glaciers during the most recentice advance. These periods of widespread glaciation are knownas ice ages. Extensive glaciers have covered large portions ofEarth many times over the last 2 million to 3 million years.During this time, glaciers advanced and retreated many timesover much of North America. The average air temperature onEarth was about 5°C lower during these ice ages than it is today.The last major advance of ice reached its maximum extent about18,000 years ago. After this last advance of glaciers, the ends ofthe ice sheets began to recede, or move back, by melting.
CANADA
UNITED STATES
MEXICO 0 500 km
Figure 13 Continental glaciersand valley glaciers are agentsof erosion and deposition. Thiscontinental glacier covers a largearea in Antarctica.
Figure 14 This map shows howmuch of North America was cov-ered by continental glaciers about18,000 years ago. Observe Was your location cov-ered? If so, what evidence of gla-ciers does your area show?
John Gerlach/Visuals Unlimited
SECTION 2 Glaciers 219
Valley Glaciers Valley glaciers occur even in today’s warmer global climate. In
the high mountains where the average temperature is low enoughto prevent snow from melting during the summer, valley glaciersgrow and creep along. Figure 15 shows valley glaciers in Africa.
Evidence of Valley Glaciers If you visit the mountains,you can tell whether valley glaciers ever existed there. You mightlook for striations, then search for evidence of plucking. Glacialplucking often occurs near the top of a mountain where a gla-cier is mainly in contact with solid rock. Valley glaciers erodebowl-shaped basins, called cirques (SURKS), into the sides ofmountains. If two valley glaciers side by side erode a mountain,a long ridge called an arête (ah RAYT) forms between them. Ifvalley glaciers erode a mountain from several directions, asharpened peak called a horn might form. Figure 16 showssome features formed by valley glaciers.
Valley glaciers flow down mountain slopes and along valleys,eroding as they go. Valleys that have been eroded by glaciershave a different shape from those eroded by streams. Stream-eroded valleys are normally V-shaped. Glacially eroded valleysare U-shaped because a glacier plucks and scrapes soil and rockfrom the sides as well as from the bottom. A large U-shaped val-ley and smaller hanging valleys are illustrated in Figure 16.
Figure 15 Valley glaciers, likethese on Mount Kilimanjaro innorth Tanzania, Africa, formbetween mountain peaks that lieabove the snow line, where snowlasts all year.
Cirque
U-shaped valley
Hanging valleys
ArêtesHorn
Cirque
Valley glacier
Arêtes
Horn
Figure 16 Valley glaciers transform the mountainsover which they pass.
U-shaped valleys result when valley glaciers movethrough regions once occupied by streams. A tribu-tary glacial valley whose mouth is high above thefloor of the main valley is called a hanging valley.The discordance between the different valley floors isdue to the greater erosive power of the trunk glacier.
Bowl-shaped basins called cirques form by erosionat the start of a valley glacier. Arêtes form wheretwo adjacent valley glaciers meet and erode along, sharp ridge. Horns are sharpened peaksformed by glacial action in three or more cirques.
Gregory G. Dimijian/Photo Researchers
220 CHAPTER 8 Erosional Forces
Self Check1. Describe how glaciers move.
2. Identify two common ways in which a glacier cancause erosion.
3. Determine Till and outwash are glacial deposits.Explain how till and outwash are different.
4. Discuss How do moraines form? What are morainesmade of?
5. Think Critically Many rivers and lakes that receivewater from glacial meltwater often appear milky bluein color. What do you think might cause the milkappearance of these waters?
SummaryHow Glaciers Move and Form
• Glaciers form in regions where snow accumu-lates and remains year round.
• The weight of snow compresses the lowerlayers into ice and causes the ice to becomeplasticlike.
Ice Eroding Rock
• Glaciers are agents of erosion.
• Glacial erosion and deposition change largeareas of the Earth’s surface.
Ice Depositing Sediment
• Glaciers melt and retreat, leaving behindsediment.
• Forms of glacial deposits include till,moraines, outwash deposits and eskers.
Continental and Valley Glaciers
• Continental and valley glaciers are the twotypes of glaciers.
6. Recognize Cause and Effect Since 1900, theAlps have lost 50 percent of their ice caps, andNew Zealand’s glaciers have shrunk by 26 percent.Describe what you think some causes and effects of this glacial melting have been.
Importance of Glaciers Glaciers have had a profound effect on Earth’s surface. They
have eroded mountaintops and transformed valleys. Vast areasof the continents have sediments that were deposited by greatice sheets. Today, glaciers in polar regions and in mountainscontinue to change the surface features of Earth.
In addition to changing the appearance of Earth’s surface,glaciers leave behind sediments that are economically impor-tant, as illustrated in Figure 17. The sand and gravel depositsfrom glacial outwash and eskers are important resources. Thesedeposits are excellent starting materials for the construction ofroads and buildings.
Figure 17 Sand and graveldeposits left by glaciers are importantstarting materials for the construc-tion of roadways and buildings.
Topic: Glacial DepositsVisit for Weblinks to information about uses ofglacial deposits.
Activity List various uses of gla-cial deposits and name the methodsof removing this material.
earth.msscience.com
earth.msscience.com/self_check_quizMark E. Gibson/Visuals Unlimited
Throughout the world’s mountainous regions,200,000 valley glaciers are moving in responseto gravity.
Real-World QuestionHow is the land affected when a valley glaciermoves downslope?
Goals■ Compare stream and glacial valleys.
Materialssand *wood blocklarge plastic or metric ruler
metal tray overhead light source*stream table with reflectorice block *Alternate materials
books (2 or 3)
Safety Precautions
WARNINGS: Do not pour sand down the drain.Make sure source is plugged into a GFI electricaloutlet. Do not touch light source—it may be hot.
Procedure1. Set up the large tray of sand as shown
above. Place books under one end of thetray to make a slope.
2. Cut a narrow riverlike channel through thesand. Measure and record its width and depthin a table similar to the one shown. Draw asketch that includes these measurements.
3. Position the overhead light source to shineon the channel as shown.
4. Force the ice block into the channel at theupper end of the tray.
5. Gently push the ice along the channel untilit’s halfway between the top and bottom of the tray, and directly under the light.
6. Turn on the light and allow the ice to melt.Record what happens.
7. Record the width and depth of the ice chan-nel in the table. Make a scale drawing.
Conclude and Apply1. Explain how you can determine the direc-
tion that a glacier traveled from the locationof deposits.
2. Explain how you can determine the direc-tion of glacial movement from sedimentsdeposited by meltwater.
3. Describe how valley glaciers affect the sur-face over which they move.
LAB 221
Glacier Data
Sample Width Depth Observations
Data (cm) (cm)
Original 1–2 3 Stream channelchannel looked V-shaped
Glacierchannel
Meltwaterchannel
GLACIAL GROOVING
Timothy Fuller
Do not write inthis book.
Wind ErosionWhen air moves, it picks up loose material and transports it
to other places. Air differs from other erosional forces because itusually cannot pick up heavy sediments. Unlike rivers that movein confined places like channels and valleys, wind carries anddeposits sediments over large areas. For example, wind is capa-ble of picking up and carrying dust particles from fields or vol-canic ash high into the atmosphere and depositing themthousands of kilometers away.
Deflation Wind erodes Earth’s surface by deflation (dih FLAYshun) and abrasion (uh BRAY zhun). When wind erodes bydeflation, it blows across loose sediment, removing small parti-cles such as silt and sand. The heavier, coarser material is leftbehind.
Abrasion When windblown sediment strikes rock, the surfaceof the rock gets scraped and worn away by a process calledabrasion. Abrasion, shown in Figure 18, is similar to sandblast-ing. Workers use machines that spray a mixture of sand and waterunder high pressure against a building. The friction wears awaydirt from stone, concrete, or brick walls. It also polishes the wallsof buildings by breaking away small pieces and leaving an even,smooth finish. Wind acts like a sandblasting machine, bouncingand blowing sand grains along. These sand grains strike against
rocks and break off small fragments. The rocksbecome pitted and are worn down gradually.
How is wind abrasion similar tosandblasting?
Deflation and abrasion happen to all land sur-faces but occur mostly in deserts, beaches, andplowed fields. These areas have fewer plants to holdthe sediments in place. When winds blow overthem, they can be eroded rapidly. Grassland orpasture land have many plants that hold the soil inplace, therefore there is little soil erosion caused bythe wind.
■ Explain how wind causes defla-tion and abrasion.
■ Recognize how loess and dunesform.
Wind erosion and depositionchange landscapes, especially indry climates.
Review Vocabularyfriction: force that opposes themotion of an object when theobject is in contact with anotherobject or surface
New Vocabulary
• deflation • loess
• abrasion • dune
Wind
222
Figure 18 The odd shape ofthis boulder was produced bywind abrasion.
Gal
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Sandstorms Even when the wind blows strongly, it seldomcarries sand grains higher than 0.5 m from the ground.However, sandstorms do occur. When the wind blows forcefullyin the sandy parts of deserts, sand grains bounce along and hitother sand grains, causing more and more grains to rise into theair. These windblown sand grains form a low cloud just abovethe ground. Most sandstorms occur in deserts, but they canoccur in other arid regions.
Dust Storms When soil is moist, it stays packed on theground, but when it dries out, it can be eroded by wind. Soil iscomposed largely of silt- and clay-sized particles. Because thesesmall particles weigh less than sand-sized particles of the samematerial, wind can move them high into the air.
Silt and clay particles are small and stick together. A fasterwind is needed to lift these fine particles of soil than is neededto lift grains of sand. However, after they are airborne, the windcan carry them long distances. Where the land is dry, duststorms can cover hundreds of kilometers. These storms blowtopsoil from open fields, overgrazed areas, and places where veg-etation has disappeared. In the 1930s, silt and dust that waspicked up in Kansas fell in New England and in the NorthAtlantic Ocean. Dust blown from the Sahara has been traced asfar away as the West Indies—a distance of at least 6,000 km.
SECTION 3 Wind 223
Dust Bowl Poor agricul-tural practices and a longperiod of sustained droughtcaused the Dust Bowl ofthe 1930s. Research howthis affected the livelihoodof the people of the south-ern plains.
What factors affect wind erosion?
Many factors compoundthe effects of wind ero-
sion. But can anything bedone to minimize erosion?
Identifying the Problem Wind velocity and duration,
the size of sediment particles,the size of the area subjectedto the wind, and the amount ofvegetation present all affect howmuch soil is eroded by wind. The tableshows different combinations of thesefactors. It also includes an erosion ratingthat depends upon what factors pertainto an area.
Solving the Problem 1. Looking at the table, can you figure out
which factors increase and which factorsdecrease the amount of erosion?
2. From what you’ve discovered, canyou estimate the missing erosion rating?
Factors That Affect Wind Erosion
Factor Descriptions
Wind velocity high high low low low
Duration of wind long long short long long
Particle size coarse medium coarse coarse medium
Surface area large large small small large
Amount of vegetation high low high high high
Erosion rating some a lot a little some ?
Reducing Wind Erosion As you’ve learned, wind erosion is mostcommon where there are no plants to pro-
tect the soil. Therefore, one of the best ways to slow or stop winderosion is to plant vegetation. This practice helps conserve soiland protect valuable farmland.
Windbreaks People in many countries plant vegetation toreduce wind erosion. For centuries, farmers have planted treesalong their fields to act as windbreaks that prevent soil erosion.As the wind hits the trees, its energy of motion is reduced. It nolonger is able to lift particles.
In one study, a thin belt of cottonwood trees reduced theeffect of a 25-km/h wind to about 66 percent of its normalspeed, or to about 16.5 km/h. Tree belts also trap snow and holdit on land. This increases the moisture level of the soil, whichhelps prevent further erosion.
Roots Along many seacoasts and deserts, vegetation is plantedto reduce erosion. Plants with fibrous root systems, such asgrasses, work best at stopping wind erosion. Grass roots areshallow and slender with many fibers. They twist and turnbetween particles in the soil and hold it in place.
Planting vegetation is a good way to reduce the effects ofdeflation and abrasion. Even so, if the wind is strong and the soilis dry, nothing can stop erosion completely. Figure 19 shows aproject designed to decrease wind erosion.
Figure 19 Rows of grasses androcks were installed on thesedunes in Qinghai, China, to reducewind erosion.
Observing How SoilIs Held in Place
Procedure1. Obtain a piece of sod
(a chunk of soil about 5 cmthick with grass growingfrom it).
2. Carefully remove soil fromthe sod roots by hand.Examine the roots with amagnifying lens.
3. Wash hands thoroughlywith soap and water.
Analysis1. Draw several of these roots
in your Science Journal.2. What characteristics of
grass roots help hold soil inplace and thus reduceerosion?
224 CHAPTER 8 Erosional Forces
Topic: ConservationPracticesVisit for Weblinks to collect data on variousmethods of protecting soil fromwind erosion.
Activity List methods that con-serve soil. What is the most com-monly used method by farmers?
earth.msscience.com
Fletcher & Baylis/Photo Researchers
Deposition by Wind Sediments blown away by wind eventually are deposited.
Over time, these windblown deposits develop into landforms,such as dunes and accumulations of loess.
Loess Some examples of large deposits of windblown sedi-ments are found near the Mississippi and Missouri Rivers. Thesewind deposits of fine-grained sediments known as loess (LES)are shown in Figure 20. Strong winds that blew across glacialoutwash areas carried the sediments and deposited them. Thesediments settled on hilltops and in valleys. Once there, the par-ticles packed together, creating a thick, unlayered, yellowish-brown-colored deposit. Loess is as fine as talcum powder. Manyfarmlands of the midwestern United States have fertile soils thatdeveloped from loess deposits.
Dunes Do you notice what happens when wind blows sedi-ments against an obstacle such as a rock or a clump of vegeta-tion? The wind sweeps around or over the obstacle. Like a river,air drops sediment when its energy decreases. Sediment starts tobuild up behind the obstacle. The sediment itself then becomesan obstacle, trapping even more material. If the wind blows longenough, the mound will become a dune, as shown in Figure 21.A dune (DOON) is a mound of sediments drifted by the wind.
What is a dune?
Dunes are common in desert regions. You also can see sanddunes along the shores of oceans, seas, or lakes. If dry sedimentsexist in an area where prevailing winds or sea breezes blow daily,dunes build up. Sand or other sediment will continue to buildup and form a dune until the sand runs out or theobstruction is removed. Some desert sand dunes cangrow to 100 m high, but most are much shorter.
Moving Dunes A sand dune has two sides. Theside facing the wind has a gentler slope. The sideaway from the wind is steeper. Examining the shapeof a dune tells you the direction from which thewind usually blows.
Unless sand dunes are planted with grasses, mostdunes move, or migrate away from the direction ofthe wind. This process is shown in Figure 22. Somedunes are known as traveling dunes because theymove rapidly across desert areas. As they lose sandon one side, they build it up on the other.
Figure 20 This sedimentdeposit is composed partially ofwindblown loess.
Figure 21 Loose sediment ofany type can form a dune ifenough of it is present and anobstacle lies in the path of thewind.
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VISUALIZING HOW DUNES FORM AND MIGRATE
Dune migration
Sand grainsaccumulateand thencascadedown the steep face.
Sand grains blow andbounce up the dune.
226
Sand blown loose from dry desert soil often builds upinto dunes. A dune may
begin to form when windblownsand is deposited in the shelteredarea behind an obstacle, such as arock outcrop. The sand pile growsas more grains accumulate. Asshown in the diagram at right,dunes are mobile, graduallymoved along by wind.
A dune migrates as sand blows up its sloping side and then cas-cades down the steeper side. Gradually, a dune moves forward—inthe same direction that the wind is blowing—as sand, lost fromone side, piles up on the other side.
▼
The dunes at left are coastal dunes fromthe Laguna Madre region of South Texas onthe Gulf of Mexico. Note the vegetation in thephoto, which has served as an obstacle totrap sand.
▼
Dunes are made of sedimentseroded from local materials.Although many dunes are com-posed of quartz and feldspar, thebrilliant white dunes in WhiteSands National Park, New Mexico,are made of gypsum.
▼
Deserts may expand whenhumans move into the transitionzone between habitable land anddesert. Here, villagers in Mauritaniain northwestern Africa shovel thesand that encroaches on theirschoolhouse daily.
▼
226 CHAPTER 8 Erosional Forces
(tl)Stephen J. Krasemann/Photo Researchers, (tr)Steve McCurry, (b)Wyman P. Meinzer, (bkgd)Breck P. Kent/Earth Scenes
Self Check1. Compare and contrast abrasion and deflation. Describe
how they affect the surface of Earth.
2. Explain the differences between dust storms and sand-storms. Describe how energy of motion affects thedeposition of sand and dust by these storms.
3. Think Critically You notice that sand is piling upbehind a fence outside your apartment building.Explain why this occurs.
SummaryWind Erosion
• Air movement picks up loose material andtransports it to other places.
• Deflation and abrasion happen mainly indeserts, beaches, and plowed fields.
Reducing Wind Erosion
• Planting vegetation can reduce wind erosion.
• Farmers use windbreaks to protect their cropfields from wind erosion.
Deposition by Wind
• Windblown deposits develop into landforms,such as dunes and accumulation of loess.
• Many farmlands of the midwestern UnitedStates have fertile soils that developed fromloess deposits.
4. Solve One-Step Equations Between 1972 and 1992,the Sahara increased by nearly 700 km2 in Mali andthe Sudan. Calculate the average number of squarekilometers the desert increased each year between1972 and 1992.
Dune Shape The shape of a dune depends onthe amount of sand or other sediment available,the wind speed and direction, and the amountof vegetation present. One common dune shapeis a crescent-shaped dune known as a barchan(BAR kun) dune. The open side of a barchandune faces the direction that the wind is blowing.When viewed from above, the points of the cres-cent are directed downwind. This type of duneforms on hard surfaces where the sand supply islimited.
Another common type of dune, called atransverse dune, forms where sand is abundant.Transverse dunes are so named because the longdirections of these dunes are perpendicular tothe general wind direction. In regions where the wind directionchanges, star dunes, shown in Figure 23, form pointed struc-tures. Other dune forms also exist, some of which show a com-bination of features.
Shifting Sediments When dunes and loess form, the land-scape changes. Wind, like gravity, running water, and glaciers,shapes the land. New landforms created by these agents of erosionare themselves being eroded. Erosion and deposition are part of acycle of change that constantly shapes and reshapes the land.
Figure 23 Star dunes form inareas where the wind blows fromseveral different directions.
SECTION 3 Wind 227earth.msscience.com/self_check_quizJohn Giustina/FPG/Getty Images
Design Your OwnDesign Your Own
Goals■ Observe the effects of
soil moisture and windspeed on wind erosion.
■ Design and carry outexperiments that testthe effects of soil mois-ture and wind speed onwind erosion.
Possible Materialsflat pans (4)fine sand (400 mL)gravel (400 mL)hair dryersprinkling canwater28-cm � 35-cm cardboard
sheets (4)tapemixing bowlmetric rulerwind speed indicator
Safety Precautions
Wear your safety gogglesat all times when usingthe hair dryer on sedi-ments. Make sure thedryer is plugged into aGFI electrical outlet.
Blowing in the WindReal-World Question
Have you ever played a sport outside and suddenly had the wind blow dust into your eyes? What did you do? Turn your back? Cover your eyes? How does wind pick up sediment? Why does wind pick up some sediments and leave others on the ground? What factors affect wind erosion?
Form a HypothesisHow does moisture in sediment affect the ability of wind to erodesediments? Does the speed of the wind limit the size of sedimentsit can transport? Form a hypothesis about how sediment moistureaffects wind erosion. Form another hypothesis about how wind speed affects the size of the sediment the wind can transport.
Test Your HypothesisMake a Plan1. As a group, agree upon and write your hypothesis statements.
2. List the steps needed to test your first hypothesis. Plan specificsteps and vary only one factor at a time. Then, list the steps neededto test your second hypothesis. Test only one factor at a time.
228 CHAPTER 8 Erosional Forces(t)Greg Vaughn/Tom Stack & Assoc., (b)Matt Meadows
3. Mix the sediments in the pans. Plan how you will foldcardboard sheets and attach them to the pans to keepsediments contained.
4. Design data tables in your Science Journal. Use them asyour group collects data.
5. Identify all constants, variables, and controls of theexperiment. One example of a control is a pan of sedimentnot subjected to any wind.
Follow Your Plan1. Make sure your teacher approves your plan before you start.
2. Carry out the experiments as planned.
3. While doing the experiments, write any observations thatyou or other members of your group make. Summarizeyour data in the data tables you designed in your ScienceJournal.
Analyze Your Data1. Compare your results with those of other groups. Explain what might have
caused any differences among the groups.
2. Explain the relationship that exists between the speed of the wind and the sizeof the sediments it transports.
Conclude and Apply1. How does energy of motion of the wind influence sediment transport? What is
the general relationship between wind speed and erosion?
2. Explain the relationship between the sediment moisture and the amount ofsediment moved by the wind.
Sediment Movement
Sediment Wind Sediment
Speed Moved
Fine sand low(dry) high
Fine sand low(wet) high
Gravel low(dry) high
Gravel low(wet) high
Fine sand and lowgravel (dry) high
Fine sand and lowgravel (wet) high
Design a table that summarizes the resultsof your experiment, and use it to explainyour interpretations to others in the class.
LAB 229
Do notwrite inthis book.
Find Out About ItVisit to learn about landslides. When is a landslide
called a mudflow? In which U.S. states are mudflows most likely to occur?earth.msscience.com/science_stats
Losing Against ErosionDid you know...
230 CHAPTER 8 Erosional Forces
...Some sand dunes migrate asmuch as 30 m per year. In a coastal regionof France, traveling dunes have buriedfarms and villages. The dunes were haltedby anti-erosion practices, such as plantinggrass in the sand and growing a barrier oftrees between the dunes and farmland.
If a sand dune is travelingat 30 m per year, how many meters does it travel in onemonth?
...In 1959, an earthquaketriggered a mass movement in MadisonRiver Canyon, Montana. About 21 millionkm3 of rock and soil slid down the canyonat an estimated 160 km/h. This typeof mass movement of earth is calleda rock slide.
...Glaciers, one of nature’s mostpowerful erosional forces, canmove more than 30 m per day. In oneweek, a fast-moving glacier can travelthe length of almost two football fields.Glaciers such as these are unusual—mostmove less than 10 cm per day.
(t)World Class Images, (c)Yann Arthus-Bertrand/CORBIS, (b)AP/Wide World Photos
Copy and complete the following concept map on erosional forces. Use the following terms andphrases: striations, leaning trees and structures, curved scar on slope, deflation, and mudflows.
Erosion by Gravity
1. Erosion is the process that picks up andtransports sediment.
2. Deposition occurs when an agent oferosion loses its energy and can no longercarry its load of sediment.
3. Slump, creep, rock slides, and mudflows areall mass movements caused by gravity.
Glaciers
1. Glaciers are powerful agents of erosion. Aswater freezes and thaws in cracks, it breaksoff pieces of surrounding rock. These piecesthen are incorporated into glacial ice byplucking.
2. As sediment embedded in the base of aglacier moves across the land, grooves and striations form. Glaciers deposit two kindsof material—till and outwash.
Wind
1. Deflation occurs when wind erodes onlyfine-grained sediments, leaving coarsesediments behind.
2. The pitting and polishing of rocks andgrains of sediment by windblown sedimentis called abrasion.
3. Wind deposits include loess and dunes. Loessconsists of fine-grained particles such as siltand clay. Dunes form when windblownsediments accumulate behind an obstacle.
CHAPTER STUDY GUIDE 231
Abrasion
ErosionalForces
Slump CreepRock slides
and rockfalls
Destruction of structures
at base ofrocky slope
Fan-shaped deposit of sediments
U-shapedvalleys
Glaciers Wind
Gravity
earth.msscience.com/interactive_tutor
Each phrase below describes a vocabulary wordfrom the list. In your Science Journal, write theterm that matches each description.
1. loess, dunes, and moraines are examples
2. slowest mass movement
3. ice picking up pieces of rock
4. much like sandblasting
5. gravity transport of material downslope
6. sand and gravel deposited by meltwater
7. glacial deposit composed of sediment withmany sizes and shapes
Choose the word or phrase that best answers thequestion.
8. Which term is an example of a feature cre-ated by deposition?A) cirque C) striationB) abrasion D) dune
9. The best plants for reducing wind erosionhave what type of root system?A) taproot C) fibrous B) striated D) sheet
10. What does a valley glacier create at thepoint where it starts?A) esker C) tillB) moraine D) cirque
Use the photo below to answer question 11.
11. Which of the following is suggested byleaning trees curving upright on a hillside?A) abrasion C) slumpB) creep D) mudflow
12. What shape do glacier-created valleys have?A) V-shape C) U-shapeB) L-shape D) S-shape
13. Which is formed by glacial erosion?A) eskers C) morainesB) arêtes D) warmer climate
14. What type of wind erosion leaves pebblesand boulders behind?A) deflation C) abrasionB) loess D) sandblasting
15. What is a ridge formed by deposition oftill called?A) striation C) cirqueB) esker D) moraine
16. What is the material called that is depositedby meltwater beyond the end of a glacier?A) eskerB) cirqueC) outwashD) moraine
232 CHAPTER REVIEW
abrasion p. 222creep p. 212deflation p. 222deposition p. 211dune p. 225erosion p. 210glacier p. 215
loess p. 225mass movement p. 211moraine p. 217outwash p. 217plucking p. 216slump p. 211till p. 216
earth.msscience.com/vocabulary_puzzlemakerJohn D. Cunningham/Visuals Unlimited
CHAPTER REVIEW 233
29. Slope Gravity is a very powerful erosional force.This means the steeper a slope is, the more soilwill move. A person can calculate how steep aslope is by using the height (rise) divided by thelength (run). This answer is then multiplied by100 to get percent slope. If you had a slope15 m high and 50 m long, what would be thepercent slope?
30. Traveling Sand A sand dune can travel upto 30 m per year. How far does the sand dunemove per day?
17. Explain how striations can give informationabout the direction that a glacier moved.
18. Describe how effective a retaining wallmade of fine wire mesh would be againsterosion.
19. Determine what can be done to prevent themigration of beach dunes.
20. Recognize Cause and Effect A researcher findsevidence of movement of ice within a gla-cier. Explain how this movement couldoccur.
21. Think Critically The end of a valley glacier isat a lower elevation than its point of ori-gin is. How does this help explain meltingat its end while snow and ice still are accu-mulating where it originated?
22. Make and Use Tables Make a table to contrastcontinental and valley glaciers.
23. Concept Map Copy and complete the events-chain concept map below to show how asand dune forms. Use the terms andphrases: sand accumulates, dune, dry sand,and obstruction traps.
24. Form a Hypothesis Hypothesize why silt inloess deposits is transported farther thansand in dune deposits.
25. Test a Hypothesis Explain how to test theeffect of glacial thickness on a glacier’sability to erode.
26. Classify the following as erosional or depo-sitional features: loess, cirque, U-shapedvalley, sand dune, abraded rock, striation,and moraine.
27. Poster Make a poster with magazine photosshowing glacial features in North America.Add a map to locate each feature.
28. Design an experiment to see how the amountof moisture added to sediments affectsmass movement. Keep all variables con-stant except the amount of moisture in thesediment. Try your experiment.
Wind blows
15 m (rise)Slope
50 m (run)
earth.msscience.com/chapter_review
Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.
Use the illustration below to answer question 1.
1. Which type of mass movement is shownabove?A. slump C. rock slideB. creep D. mudflow
2. Which term refers to sediment that isdeposited by glacier ice?A. outwash C. loessB. till D. esker
3. During which process does wind pick upfine sediment?A. abrasionB. mass movementC. deflationD. deposition
4. On which of the following continents docontinental glaciers exist today?A. Antarctica C. AustraliaB. Africa D. Europe
5. Which forms when a rock in glacier iceslides over Earth’s surface?A. moraine C. hornB. esker D. groove
6. What causes sediment and rock to moveto lower elevations through time?A. sunlight C. gravityB. plant roots D. dust storms
7. Which can reduce wind erosion?A. windbreaks C. eskersB. dunes D. horns
8. Which consists of fine-grained, wind-blown sediment?A. moraine C. tillB. loess D. rock fall
Use the diagram below to answer questions 9–11.
9. Which term describes point X?A. horn C. cirqueB. arête D. hanging valley
10. Which term describes point Z?A. horn C. cirqueB. arête D. hanging valley
11. Which agent of erosion created the land-scape in the diagram?A. wind C. gravityB. water D. ice
Y
Z
W X
234 STANDARDIZED TEST PRACTICE
Take Your Time Stay focused during the test and don’t rush,even if you notice that other students are finishing the test early.
STANDARDIZED TEST PRACTICE 235
Record your answers on the answer sheet providedby your teacher or on a separate sheet of paper.
12. Give three examples of erosion? How doesit affect Earth’s surface?
13. What is deposition? Give three examplesof how it changes Earth’s surface.
14. How is a rock fall different from a rockslide? Use a labeled diagram to supportyour answer.
15. Explain how a glacier can erode the land,and then describe three forms of glacialdeposition.
The graph below shows data about how much water
flows through a stream. The stream is fed by glacial
meltwater. Use the graph to answer questions 16–18.
16. What were the lowest and highestamounts of stream flow on July 6th?
17. What were the lowest and highestamounts of stream flow on July 8th?
18. Notice that these data were obtained in July.Explain why the amount of stream flowfrom a glacier would vary each day. Givethree examples to support your reasoning.
Record your answers on a sheet of paper.
Use the diagram below to answer questions 19–22.
19. Describe the process that causes sand tomove up the less steep side of the dune. Usea labeled diagram to support your answer.
20. Why does sand move down the steeperside of the dune? Use a labeled diagram tosupport your answer.
21. Design three time-lapse illustrations toshow how sand dunes move across land.
22. Describe three ways to slow down themovement of sand dunes.
23. What types of damage are caused bylandslides? How are people affected bylandslides physically and economically?
24. Give three ways that damage from land-slides can be reduced.
25. What is a dust storm? Where would youexpect dust storms to occur? Give twosafety suggestions for people caught in adust storm.
26. Describe two ways that glacier ice canmove across the surface.
27. How is creep different from most othertypes of mass movement? Explain theforces that cause creep, as well as theeffect of creep.
28. Create a chart to show how continentalglaciers are different from valley glaciers.Include their causes, physical features, andgeological effects on the land.
Glacial Stream Flow
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earth.msscience.com/standardized_test
