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Weatheringand Erosionsections1 Weathering and SoilFormationLab Classifying Soils2 Erosion of Earth’s SurfaceLab Measuring Soil ErosionVirtual Lab How are Earth’smaterials broken down?What happened to his face?Well, how would you feel if wind, sand, andrain blew in your face for over 5,000 years?Don’t forget the blistering sun and nightlychill! Would you feel weathered and torn?Two processes help shape Earth’s surface—weathering and erosion.Science Journal Describe a place—a home, a park,river, or mountain. What would happen in a year, a hundredyears, even 5,000 years?314Carmen Redondo/CORBIS

Start-Up ActivitiesWater’s ForceThe Grand Canyon is 446 km long, up to 29km wide, and up to 1,829 m deep. The waterof the Colorado River carved the canyon outof rock by wearing away particles and carryingthem away for millions of years. Overtime, erosion has shaped and reshapedEarth’s surface many times. In this lab, youwill explore how running water formed theGrand Canyon.1. Fill a bread pan with packed sand andform a smooth, even surface.2. Place the bread pan in a plastic wash tub.Position one end of the washtub in a sinkunder the faucet.3. Place a brick or wood block under the endof the bread pan beneath the faucet.4. Turn on the water to form a steady trickleof water falling into the pan and observefor 10 min. The washtub should catch theeroded sand.5. Think Critically In your Science Journal,draw a top view picture of the erosionpattern formed in the sand by the runningwater. Write a paragraph describing whatthe sand would look like if you had leftthe water running overnight.STEP 1STEP 2STEP 3STEP 3Weathering and ErosionMake the following Foldableto compare and contrast weatheringand erosion.Fold one sheet of paper lengthwise.Fold into thirds.Unfold and draw overlapping ovals.Cut the top sheet along the folds.Label the ovals as shown.Weathering Both ErosionConstruct a Venn Diagram As you read thechapter, list the characteristics unique to weatheringunder the left tab, those unique to erosionunder the right tab, and those characteristicscommon to both under the middle tab.Preview this chapter’s contentand activities atred.msscience.com315

Weathering andSoil Formation■ Identify processes that breakrock apart.■ Describe processes that chemicallychange rock.■ Explain how soil evolves.Soil forms when rocks break apartand change chemically. Soil is hometo many organisms, and mostplants need soil in order to grow.Review Vocabularyacid rain: acidic moisture, with apH below 5.6New Vocabularyweatheringmechanical weatheringchemical weathering• soiltopographyWeatheringHave you noticed potholes in roadways and broken concretein sidewalks and curbs? When a car rolls over a pothole in theroad in late winter or when you step over a broken sidewalk, youknow things aren’t as solid or permanent as they look. Holes inroads and broken sidewalks show that solid materials can bechanged by nature. Weathering is a mechanical or chemical surfaceprocess that breaks rocks into smaller pieces. Freezing andthawing, oxygen in the air, and even plants and animals canaffect the stability of rock. These are some of the things thatcause rocks on Earth’s surface to weather, and in some cases, tobecome soils.Mechanical WeatheringWhen a sidewalk breaks apart, a large slab of concrete is brokeninto many small pieces. The concrete looks the same. It’s justbroken apart. This is similar to mechanical weathering of rocks.Mechanical weathering breaks rocks into smaller pieces withoutchanging them chemically. The small pieces are identical incomposition to the original rock, as shown in Figure 1. Two ofthe many causes of mechanical weathering are ice wedging andliving organisms.Figure 1 The forces of mechanicalweathering break apart rocks.Describe how you know that thesmaller pieces of granite were producedby mechanical weathering.316Jonathan Blair/CORBIS

Figure 2 Over time, freezing water can break apart rock.Water seeps into cracks.The deeper the cracks are, thedeeper water can seep in.The water freezes and expands,forcing the cracks to open further.The ice melts. If the temperaturefalls below freezing again, theprocess will repeat itself.Ice Wedging In some areas of the world, air temperaturedrops low enough to freeze water. Then, when the temperaturerises, the ice thaws. This freezing and thawing cycle breaks uprocks. How can this happen? When it rains or snow melts, waterseeps into cracks in rocks. If the temperature drops below freezing,ice crystals form. As the crystals grow, they take upmore space than the water did because when waterfreezes, its molecules move apart. This expansion exertspressure on the rocks. With enough force, the rocks willcrack further and eventually break apart, as shown inFigure 2. Ice wedging also causes potholes to form inroadways.Figure 3 Tree roots can breakrock apart.Explain how ice wedging canbreak rock apart.Plants and Animals Plants and animals also causemechanical weathering. As shown in Figure 3, plantscan grow in what seem to be the most inconvenientplaces. Their roots grow deep into cracks in rock wherewater collects. As they grow, roots become thicker andlonger, slowly exerting pressure and wedging rockapart.Gophers and prairie dogs also weather rock—as doother animals that burrow in the ground. As they burrowthrough sediment or soft sedimentary rock, animalsbreak rock apart. They also push some rock and sedimentto the surface where another kind of weathering,called chemical weathering, takes place more rapidly.SECTION 1 Weathering and Soil Formation 317R. & E. Thane/Earth Scenes

Figure 4 Chemical weatheringchanges the chemical compositionof minerals and rocks.Describe how kaolinite is differentfrom feldspar.Elements in Feldspar8%Aluminum8%23%PotassiumSilicon61%OxygenElements in Kaolinite12%Aluminum12%Silicon23%Hydrogen53%OxygenFeldspar crystals react withcarbonic acid.The mineral kaolinite isformed.Chemical WeatheringChemical weathering occurs when the chemical compositionof rock changes. This kind of weathering is rapid in tropicalregions where it’s moist and warm most of the time. Becausedesert areas have little rainfall and polar regions have low temperatures,chemical weathering occurs slowly in these areas.Table 1 summarizes the rates of chemical weathering for differentclimates. Two important causes of chemical weathering arenatural acids and oxygen.Why is chemical weathering rapid inthe tropics?Table 1 Rates of WeatheringClimateHot and dryHot and wetCold and dryCold and wetChemicalWeatheringSlowFastSlowSlowNatural Acids Some rocksreact chemically with naturalacids in the environment. When water mixes with carbondioxide in air or soil, for example, carbonic acidforms. Carbonic acid can change the chemical compositionof minerals in rocks, as shown in Figure 4.Although carbonic acid is weak, it reacts chemicallywith many rocks. Vinegar reacts with the calcium carbonatein chalk, dissolving it. In a similar way, whencarbonic acid comes in contact with rocks like limestone,dolomite, and marble, they dissolve. Other rocksalso weather when exposed to carbonic acid.318 CHAPTER 11 Weathering and ErosionDoug Martin

Plant Acids Plant roots also produceacid that reacts with rocks. Manyplants produce a substance called tannin.In solution, tannin forms tannicacid. This acid dissolves some mineralsin rocks. When minerals dissolve, theremaining rock is weakened, and it canbreak into smaller pieces. The nexttime you see moss or other plantsgrowing on rock, as shown in Figure 5,peel back the plant. You’ll likely see discolorationof the rock where plantacids are reacting chemically with someof the minerals in the rock.Effect of Oxygen When you see rusty cars, reddish soil, orreddish stains on rock, you are witnessing oxidation, the effectsof chemical changes caused by oxygen. When iron-containingmaterials such as steel are oxidized, a chemical reaction causesthe material to rust. Rocks chemically weather in a similar way.When some iron-containing minerals are exposed to oxygen,they can weather to minerals that are like rust. This leaves therock weakened, and it can break apart. As shown in Figure 6,some rocks also can be colored red or orange when iron-bearingminerals in them react with oxygen.Figure 6 Oxidation occurs in rocks and cars.Even a tiny amount of iron in rockcan combine with oxygen and forma reddish iron oxide.The iron contained in metal objectssuch as this truck also can combinewith oxygen and form a reddishiron oxide called rust.Figure 5 Moss growing on rockscan cause chemical weathering.Dissolving Rockwith AcidsProcedureWARNING: Do not removegoggles until lab cleanup andhandwashing are completed.1. Use an eyedropper to putseveral drops of vinegar onpieces of chalk and limestone.Observe the resultswith a magnifying lens.2. Put several drops of 5%hydrochloric acid on thechalk and limestone.Observe the results.Analysis1. Describe the effect of thehydrochloric acid and vinegaron chalk and limestone.2. Research what type of acidvinegar contains.SECTION 1 Weathering and Soil Formation 319(t)Aaron Haupt, (bl)Layne Kennedy/CORBIS, (br)Richard Cummins/CORBIS

Table 2 Factors that Affect Soil FormationParent Rock Slope of Land Climate Time OrganismsSoilIs soil merely dirt under your feet, or is it something moreimportant? Soil is a mixture of weathered rock, organic matter,water, and air that supports the growth of plant life. Organicmatter includes decomposed leaves, twigs, roots, and othermaterial. Many factors affect soil formation.Analyzing SoilsProcedure1. Obtain a sample of soilfrom near your home.2. Spread the soil out over apiece of newspaper.3. Carefully sort through thesoil. Separate out organicmatter from weatheredrock.4. Wash hands thoroughlyafter working with soils.Analysis1. Besides the organic materialsand the remains ofweathered rock, what elseis present in the soil?2. Is some of the soil toofine-grained to tell ifit is organic orweatheredrock?Parent Rock As listed in Table 2, one factor affecting soilformation is the kind of parent rock that is being weathered. Forexample, where limestone is chemically weathered, clayey soil iscommon because clay is left behind when the limestone dissolves.In areas where sandstone is weathered, sandy soil forms.The Slope of the Land The topography, or surface features,of an area also influence the types of soils that develop. You’veprobably noticed that on steep hillsides, soil has little chance ofdeveloping. This is because rock fragments move downhill constantly.However, in lowlands where the land is flat, wind andwater deposit fine sediments that help form thick soils.Climate Climate affects soil evolution, too. If rock weathersquickly, deep soils can develop rapidly. This is more likely to happenin tropical regions where the climate is warm and moist.Climate also affects the amount of organic material in soil. Soils indesert climates contain little organic material. However, in warm,humid climates, vegetation is lush and much organic material ispresent. When plants and animals die, decomposition by fungiand bacteria begins. The result is the formation of a dark-coloredmaterial called humus, as shown in the soil profile in Figure 7.Most of the organic matter in soil is humus. Humus helps soil holdwater and provides nutrients that plants need to grow.320 CHAPTER 11 Weathering and Erosion

Time It takes time for rocks to weather. It can takethousands of years for some soils to form. As soilsdevelop, they become less like the rock from whichthey formed. In young soils, the parent rock determinesthe soil characteristics. As weathering continues,however, the soil resembles the parent rock less andless. Thicker, well-developed soils often are found inareas where weathering has gone on undisturbed for along period of time. For this to happen, soil materialsmust not be eroded away and new sediment must notbe deposited over the land’s surface too quickly.Organisms Organisms influence soil development.Lichens are small organisms that consist of an alga anda fungus that live together for mutual benefit. You mayhave seen lichens in the form of multicolored patchesgrowing on tree branches or cliff faces. Interestingly,lichens can grow directly on rock. As they grow, theytake nutrients from the rock that they are starting tobreak down, forming a thin soil. After a soil hasformed, many types of plants such as grasses and treescan grow.The roots of these plants further break down the parent rock.Dead plant material such as leaves accumulates and adds organicmatter to the soil. Some plants contribute more organic matterto soil than others. For example, soil under grassy areas often isricher in organic matter than soil developing under forests. Thisis why some of the best farmland in the midwestern UnitedStates is where grasslands used to be.Humus-rich surface layer----------------------------------------------------------------Intermediate layer-----------------------------------------------------------------Slightly altered parent materialFigure 7 Soils contain layersthat are created by weathering,the flow of water and chemicals,and the activities of organisms.Explain what part microorganismsplay in soil development.SummaryMechanical Weathering•The freezing and thawing cycle breaks up rocks.Plants’ roots and burrowing animals canbreak rocks apart.•Chemical WeatheringSome rocks react chemically with naturalacids.•SoilA factor affecting soil formation is the kind ofparent rock that is being weathered.Self Check1. Describe how rocks are mechanically weathered.2. Name two agents of chemical weathering.3. Explain how carbonic acid weather rocks.4. Describe how soil forms. What factors are important?5. Think Critically How could climate affect rates ofmechanical weathering? What about chemical weathering?How are the two kinds of weathering related?6. Compare and contrast mechanical weathering causedby ice and growing roots.red.msscience.com/self_check_quizSECTION 1 Weathering and Soil Formation 321

Not all soils are the same. Geologists and soilscientists classify soils based on the amountsand kinds of particles they contain.Classifying SoilsReal-World QuestionHow is soil texture determined?Goals■ Classify a soil using an identification key.■ Observe soil with a stereomicroscope.Materialssoil samplestereomicroscope*magnifying lens*Alternate materialsSafety PrecautionsProcedure1. Place a small sample of moistened soilbetween your fingers. Then follow thedirections in the classification key below.a. Slide your fingers back and forth pasteach other. If your sample feels gritty, goto b. If it doesn’t feel gritty, go to c.b. If you can mold the soil into a firm ball,it’s sandy loam soil. If you cannot mold itinto a firm ball, it’s sandy soil.c. If your sample is sticky, go to d. If yoursample isn’t sticky, go to e.d. If your sample can be molded into a long,thin ribbon, it’s clay soil. If your soil can’tbe molded into a long, thin ribbon, it’sclay loam soil.e. If your sample is smooth, it’s silty loamsoil. If it isn’t smooth, it’s loam soil.2. After classifying your soil sample, examine itunder a microscope. Draw the particles andany other materials that you see.3. Wash your hands thoroughly after you arefinished working with soils.Conclude and Apply1. Determine the texture of your soilsample.2. Describe two characteristics of loam soil.3. Describe two features of sandy loam soil.4. Record Observations Based on yourobservations with the stereomicroscope,what types of particles and other materialsdid you see? Did you observe any evidenceof the activities of organisms?Compare your conclusions with those ofother students in your class. For more help,refer to the Science Skill Handbook.322 CHAPTER 11 Weathering and ErosionKS Studios

Erosion of Earth’s SurfaceAgents of ErosionImagine looking over the rim of the Grand Canyon at thewinding Colorado River below or watching the sunset overUtah’s famous arches. Features such as these are spectacularexamples of Earth’s natural beauty, but how can canyons andarches form in solid rock? These features and many other naturallandforms are a result of erosion of Earth’s surface. Erosion is thewearing away and removal of rock or sediment. Erosion occursbecause gravity, ice, wind, and water sculpt Earth’s surface.GravityGravity is a force that pulls every object toward every otherobject. Gravity pulls everything on Earth toward its center. As aresult, water flows downhill and rocks tumble down slopes.When gravity alone causes rock or sediment to move down aslope, the erosion is called mass movement. Mass movementscan occur anywhere there are hills or mountains. One placewhere they often occur is near volcanoes, as shown in Figure 8.Creep, slump, rock slides, and mudflows are four types of massmovements, as seen in Figure 9.■ Identify agents of erosion.■ Describe the effects of erosion.Erosion shapes Earth’s surface.Review Vocabularydeposition: dropping of sedimentsoccurs when an agent of erosioncan no longer carry its loadNew Vocabulary• erosionmassmovement• creepslumpdeflation• abrasionrunoffFigure 8 The town of Weed,California, was built on top of alandslide that moved down thevolcano known as Mount Shasta.LandslideYreka597MountShastaWeed0 15 km323USGS

VISUALIZING MASS MOVEMENTSFigure 9When the relentless tug of gravitycauses a large chunk of soil or rock tomove downhill—either gradually orwith sudden speed—the result is what geologistscall a mass movement. Weathering andwater often contribute to mass movements.Several kinds are shown here.A CREEP Whensoil on a slopemoves very slowlydownhill, a massmovement calledcreep occurs. Someof the trees at righthave been graduallybent becauseof creep’s pressureon their trunks.B SLUMP This cliff in North Dakotashows the effects of the mass movementknown as slump. Slumping oftenoccurs after earthquakes or heavy andprolonged rains.D MUDFLOWS A Japanese town shows the devastationthat a fourth type of mass movement—a mudflow—can bring. When heavy moisture saturates sediments,mudflows can develop, sending a pasty mix of waterand sediment downhill over the ground’s surface.C ROCK SLIDESWhen rocks breakfree from the sideof a cliff or amountain, theycrash down in whatis called a rock slide.Rock slides, likethe one at the left inYosemite NationalPark, can occur withlittle warning.324(tl)DP Schwert/ND State University, (tr)Martin Miller, (c)Jeff Foott/Bruce Coleman, Inc., (b)Roger Ressmeyer/CORBIS

Creep The process in whichsediments move slowly downhill,as shown in Figure 9A, is calledcreep. Creep is common wherefreezing and thawing occur. As iceexpands in soil, it pushes sedimentsup. Then as soil thaws, thesediments move farther downslope.Figure 10 shows how smallparticles of sediment can creepdownslope. Over time, creep canmove large amounts of sediment,possibly causing damage to somestructures. Do you live in an areawhere you can see the results ofcreep?CreepSoil or sedimentExpansion caused by freezingFalling caused by thawingTop of soilwhen frozenTop of soilwhen thawedSlump A slump occurs when a mass of rock or sedimentmoves downhill, leaving a curved scar, as shown in Figure 9B.Slumps are most common in thick layers of loose sediment, butthey also form in sedimentary rock. Slumps frequently occur onslopes that have been undercut by erosion, such as those abovethe bases of cliffs that have been eroded by waves. Slumping ofthis kind is common along the coast of Southern California,where it threatens to destroy houses and other buildings.Rock Slides Can you imagine millions of cubic meters ofrock roaring down a mountain at speeds greater than 250 km/h?This can happen when a rock slide occurs. During a rock slidelayers of rock break loose from slopes and slide to the bottom.The rock layers often bounce and break apart during movement.This produces a huge, jumbled pile of rocks at the bottom of theslope, as you can see in Figure 9C. Rock slides can be destructive,sometimes destroying entire villages or causing hazards onroads in mountainous areas.Mudflows Where heavy rains or melting snow and ice saturatesediments, mudflows, as shown in Figure 9D, can develop. Amudflow is a mass of wet sediment that flows downhill over theground surface. Some mudflows can be thick and flow slowlydownhill at rates of a few meters per day. Other mudflows can bemuch more fluid and move downslope at speeds approaching160 km/h. This type of mudflow is common on some volcanoes.Figure 10 When soil freezes,particles are lifted. When it thaws,the particles are pulled downhill bygravity. Eventually, large amountsof sediment are moved by thisprocess.Mass Movement Slumpsand rock slides often occurwhen sediment becomessaturated by rain. Waterbetween sediment grainshelps lift up overlying rockand sediment. This makesit easier for the sedimentto overcome the forcesholding it in place. Canyou think of a way someslopes might be protectedfrom slumps and rockslides? Explain.What is the slowest of the four kinds of massmovement?SECTION 2 Erosion of Earth’s Surface 325

Figure 11 Glaciers form in coldregions.Continental glaciersare located near thepoles, in Antarcticaand Greenland.Valley glaciers arefound at high elevationson manycontinents.Continental GlacierValley GlacierTopic: Glacial Erosion andDepositionVisit red.msscience.com for Weblinks to information about glacialerosion and deposition.Activity Research glacialerosion and describe how it hasaffected the topography in anarea.IceIn some parts of the world, ice is an agent of erosion. In coldregions, more snow might fall than melt. Over many years, thesnow can accumulate to form large, deep masses of ice called glaciers.When the ice in a glacier becomes thick enough, its ownweight causes it to flow downhill under the influence of gravity.As glaciers move over Earth’s surface, they erode materials fromsome areas and deposit sediment in other areas. Figure 11 showsthe two kinds of glaciers—continental glaciers and valley glaciers.Today, continental glaciers in polar regions cover about tenpercent of Earth. These glaciers are so large and thick that theycan bury mountain ranges. Valley glaciers are much smaller andare located in high mountains where the average temperatureisn’t warm enough to melt the ice sheets. The average flow rateof a valley glacier is 0.01 to 2.0 meters per day, but during asurge, they can flow up to 100 meters per day.Glacial Erosion Glaciers can erode rock in two different ways.If the underlying rock has cracks in it, the ice can pull out pieces ofrock. This causes the rock to erode slowly. Loose pieces of rockfreeze into the bottom of the glacier and are dragged along as theglacier moves. As these different-sized fragments of rock aredragged over Earth’s surface, they scratch the rock below like giantsheets of sandpaper. This scratching is the second way that glacierscan erode rock. Scratching produces large grooves or smaller striationsin the rock underneath. The scratching also can wear rockinto a fine powder called rock flour.326 CHAPTER 11 Weathering and Erosion(l)Chris Rainier/CORBIS, (r)Glenn M. Oliver/Visuals Unlimited

(l)John Lemker/Earth Scenes, (r)Francois Gohier/Photo Researchers, (b)Paul A. Souders/CORBISFigure 12 Many high-altitude areas owetheir distinctive appearance to glacial erosion.Mountain glaciers can carve bowl-shaped depressionscalled cirques.Glaciers can widen valleys, giving them a U-shapedprofile.Effects of Glacial Erosion Glacial erosion of rock can be apowerful force shaping Earth’s surface. In mountains, valley glacierscan remove rock from the mountaintops to form largebowls, called cirques (SURKS), and steep peaks. When a glaciermoves into a stream valley, it erodes rock along the valley sides,producing a wider, U-shaped valley. These features are shown inFigure 12. Continental glaciers also shape Earth’s surface. Theseglaciers can scour large lakes and completely remove rock layersfrom the land’s surface.Glacial Deposition Glaciers also can deposit sediments.When stagnant glacier ice melts or when ice melts at the bottomof a flowing glacier or along its edges, the sediment theice was carrying gets left behind on Earth’s surface. This sediment,deposited directly from glacier ice, is called till. Till is amixture of different-sized particles, ranging from clay to largeboulders.As you can imagine, a lot ofmelting occurs around glaciers,especially during summer. Somuch water can be producedthat streams often flow away fromthe glacier. These streams carryand deposit sediment. Sand andgravel deposits laid down by thesestreams, shown in Figure 13, arecalled outwash. Unlike till, outwashusually consists of particlesthat are all about the same size.Figure 13 This valley in NewZealand has been filled withoutwash.Explain how you could distinguishoutwash from till.327

WindIf you’ve had sand blow into your eyes, you’ve experiencedwind as an agent of erosion. When wind blows across loosesediments like silt and sand, it lifts and carries it. As shown inFigure 14, wind often leaves behind particles too heavy to move.This erosion of the land by wind is called deflation. Deflationcan lower the land’s surface by several meters.Wind that is carrying sediment can wear down, or abrade,other rocks just as a sandblasting machine would do. Abrasionis a form of erosion that can make pits in rocks and producesmooth, polished surfaces. Abrasion is common in some desertsand in some cold regions with strong winds.Figure 14 In a desert, wheresmall particles have been carriedaway by wind, larger sedimentscalled desert pavement remainbehind.Figure 15 Wind transportationof sand creates sand dunes.How does abrasion occur?When wind blows around some irregular feature on Earth’ssurface, such as a rock or clump of vegetation, it slows down.This causes sand carried by the wind to be deposited. If thissand deposit continues to grow, a sand dune like that shown inFigure 15 might form. Sand dunes move when wind carriessand up one side of the dune and it avalanches down the other,as shown in Figure 15.Sometimes, wind carries only fine sediment called silt. Whenthis sediment is deposited, an accumulation of silt called loess(LOOS) can blanket Earth’s surface. Loess is as fine as talcumpowder. Loess often is deposited downwind of large deserts anddeflated glacial outwash deposits.As wind blows over a sand dune, sand blows up thewindward side and tumbles down the other side. In thisway, a sand dune migrates across the land.DunemovementSand dunes do not remain in onelocation—they migrate.328 CHAPTER 11 Weathering and Erosion(t)Gerald & Buff Corsi/Visuals Unlimited, (b)Dean Conger/CORBIS

WaterYou probably have seen muddy water streamingdown a street after a heavy rain. You might evenhave taken off your shoes and waded through thewater. Water that flows over Earth’s surface is calledrunoff. Runoff is an important agent of erosion,especially if the water is moving fast. The morespeed water has, the more material it can carry withit. Water can flow over Earth’s surface in several differentways, as you will soon discover.Sheet Flow As raindrops land on Earth’s surface, they breakup clumps of soil and loosen small grains of sediment. If theseraindrops are falling on a sloped land surface, a thin sheet ofwater might begin to move downhill. You have observed somethingsimilar if you’ve ever washed a car and seen sheets of waterflowing over the hood, as shown in Figure 16. When water flowsdownhill as a thin sheet, it is called sheet flow. This thin sheet ofwater can carry loose sediment grains with it, causing erosion ofthe land. This erosion is called sheet erosion.Figure 16 Water flows overthe hood of a car as a thin sheet.Describe how this is similar tosheet flow on Earth’s surface.Can evidence of sheet erosion be seen in a farm field?If you’ve ever traveled through parts ofyour state where there are farms, youmight have seen bare, recently cultivatedfields. Perhaps the soil was prepared forplanting a crop of corn, oats, or soybeans.Do you think sheet erosion can visiblyaffect the soil in farm fields?Identifying the ProblemThe top layer of most soils is muchdarker than layers beneath because it containsmore organic matter. This layer isthe first to be removed from a slope bysheet flow. How does the photo show evidenceof sheet erosion?Solving the Problem1. Observe the photo and write a descriptionof it in your Science Journal.2. Infer why some areas of the field aredarker colored than others are. Wheredo you think the highest point(s) are inthis field?3. Make a generalization about the darkerareas of the field.SECTION 2 Erosion of Earth’s Surface 329(t)KS Studios, (b)Tess & David Young/Tom Stack & Assoc.

Figure 17 Gullies often form onvegetation-free slopes.(t)Gerard Lacz/Earth Scenes, (b)Vanessa Vick/Photo ResearchersTopic: Power of WaterVisit red.msscience.com for Weblinks to information about theerosional force of running water.Activity Research your watershedand see if the topographywas shaped by running water.Figure 18 Streams that flowdown steep slopes such as thisone in Yosemite National Parkoften have white-water rapidsand waterfalls.Rills and Gullies Where a sheet of water flows aroundobstacles and becomes deeper, rills can form. Rills are smallchannels cut into the sediment at Earth’s surface. These channelscarry more sediment than can be moved by sheet flow. In somecases, a network of rills can form on a slope after just one heavyrain. Large amounts of sediment can be picked up and carriedaway by rills.As runoff continues to flow through the rills, more sedimenterodes and the channel widens and deepens. When the channelsget to be about 0.5 m across, they are called gullies, as shown inFigure 17.Streams Gullies often connect to stream channels. Streamscan be so small that you could jump to the other side or largeenough for huge river barges to transport products along theircourse. Most streams have water flowing through them continually,but some have water only during part of the year.In mountainous and hilly regions, as in Figure 18, streamsflow down steep slopes. These streams have a lot of energy andoften cut into the rock beneaththeir valleys. This type of streamtypically has white-water rapidsand may have waterfalls. Asstreams move out of the mountainsand onto flatter land, theybegin to flow more smoothly. Thestreams might snake back andforth across their valley, erodingand depositing sediments alongtheir sides. All streams eventuallymust flow into the ocean or a largelake. The level of water in theocean or lake determines howdeeply a river can erode.330

Shaping Earth’s Surface In the LaunchLab, you saw a small model of erosion by astream. Streams are the most important agent oferosion on Earth. They shape more of Earth’ssurface than ice, wind, or gravity. Over long periodsof time, water moving in a stream can haveenough power to cut large canyons into solidrock. Many streams together can sculpt the landover a wide region, forming valleys and leavingsome rock as hills. Streams also shape the land bydepositing sediment. Rivers can deposit sandbarsalong their course, and can build up sheetsof sand across their valleys. When rivers enteroceans or lakes, the water slows and sediment is deposited. Thiscan form large accumulations of sediment called deltas, as inFigure 19. The city of New Orleans is built on the delta formed bythe Mississippi River.Effects of ErosionAll agents of erosion change Earth’s surface. Rock and sedimentare removed from some areas only to be deposited somewhereelse. Where material is removed, canyons, valleys, andmountain cirques can form. Where sediment accumulates, deltas,sandbars, sand dunes, and other features make up the land.Figure 19 A triangular area ofsediment near the mouth of a riveris called a delta. Ancient deltasthat are now dry land are oftenexcellent places to grow crops.SummaryGravity•Erosion of rock or sediment, moved down a•slope by gravity, is called mass movement.Creep, slump, rock slides, and mudflows arefour types of mass movement.•IceGlaciers move over Earth’s surface, erodingmaterials from some areas and depositingsediments in other areas.•WindDeflation and abrasion are two commonforms of wind erosion.Water•Runoff is water flowing over Earth’s surface.Water erosion can create sheet erosion, rills,gullies, streams, valleys, and canyons.Self Check1. Describe four agents of erosion. Which of these is thefastest? The slowest? Explain your answers.2. Explain the difference between deflation and abrasion.3. Describe how a cirque forms.4. Explain When do streams deposit sediments? When dostreams erode sediments?5. Think Critically Why might a river that was erodingand depositing sediment along its sides start to cut intoEarth to form a canyon?6. Solve One-Step Equations If wind is eroding an areaat a rate of 2 mm per year and depositing it in asmaller area at a rate of 7 mm per year, how muchlower will the first area be in meters after 2 thousandyears? How much higher will the second area be?red.msscience.com/self_check_quizSECTION 2 Erosion of Earth’s Surface 331Martin G. Miller/Visuals Unlimited

Design Your OwnMeasuryng Soil ErosionGoals■ Design an experimentto measure soil lossfrom grass-covered soiland from soil withoutgrass cover.■ Calculate the percentof soil loss with andwithout grass cover.Possible Materialsblocks of wood*bookspaint trays (2)soilgrass sodwaterpails (2)1,000-mL beakertriple-beam balancecalculatorwatch*Alternate materialsReal-World QuestionDuring urban highway construction,surface mining, forest harvesting, oragricultural cultivation, surface vegetationis removed from soil. Thesepractices expose soil to water andwind. Does vegetation significantlyreduce soil erosion? How much doesvegetation reduce soil erosion?Form a HypothesisBased on what you’ve read and observed, hypothesize abouthow a grassy field will have less erosion than a field that is bare soil.Safety PrecautionsWash your hands thoroughlywhen you arethrough working withsoils.332 CHAPTER 11 Weathering and Erosion(t)Matt Meadows, (b)Dominic Oldershaw

Test Your HypothesisMake a Plan1. As a group, agree upon the hypothesis and decide how you will test it. Identifywhich results challenge or confirm the hypothesis.2. List the steps you will need to take to test your hypothesis. Describe exactlywhat you will do in each step.3. Prepare a data table in your Science Journal to record your observations.4. Read over the entire experiment to make sure all steps are in logical order, andthat you have all necessary materials.5. Identify all constants and variables and the control of the experiment. A control isa standard for comparing the results of an experiment. One possible control for thisexperiment would be the results of the treatment of an uncovered soil sample.Follow Your Plan1. Make sure your teacher approvesyour plan before you start.2. Carry out the experiment step bystep as planned.3. While doing the experiment,record your observations andcomplete the data table in yourScience Journal.Vegetation and ErosionCoveredsoil sampleUncoveredsoil sampleAnalyze Your Data1. Compare the percent of soil loss from each soil sample.2. Compare your results with those of other groups.3. What was your control in this experiment? Why is it a control?4. Which were the variables you kept constant?Which did you vary?(A) Mass of (B) Mass of % of Soil LossSoil at Start Eroded Soil (B/A) 100Do not write in this book.Conclude and Apply1. Did the results support your hypothesis?Explain.2. Infer what effect other types of plants wouldhave in reducing soil erosion. Do you think thatgrass is better or worse than most other plantsat reducing erosion? Explain your answer.Write a letter to the editor of a newspaper.In your letter, summarize what you learnedin your experiment about the effect ofplants on soil erosion.LAB 333

SCIENCEANDHISTORYSCIENCECAN CHANGETHE COURSEOF HISTORY!Acid rain is destroyingsome of the world’s mostfamous monumentsThe Taj Mahal in India, the Acropolis inGreece, and the Colosseum in Italy havestood for centuries. They’ve survived wars,souvenir-hunters, and natural weathering fromwind and rain. But now, something far worsethreatens their existence—acidrain. Overthe last few decades,this form of pollutionhas eaten away at someof history’s greatestmonuments.Most of these structuresare made of sandstone,limestone, andmarble. Acid rain causesthe calcium in thesestones to form calciumsulfate, or gypsum.Gypsum’s powdery little blotches are sometimescalled “marble cancer.” When it rains, the gypsumwashes away, along with some of the surface of themonument.In Agra, India, the smooth, white marble mausoleumcalled the Taj Mahal has stood since theseventeenth century. But acid rain is making thesurface of the building yellow and flaky. The pollutionis caused by hundreds of factories surroundingAgra that emit damaging chemicals.Acid rain has not been kind tothis Mayan figure.What moisture, molds, and the roots of vegetationcouldn’t do in 1,500 years, acid rain is doing ina few decades. It is destroying the Mayan ruins ofMexico. Acid rain is causing statues to crumble andpaintings on walls to flake off.Acid rain is a hugeproblem affectingnational monuments andtreasures in just aboutevery urban location inthe world. These includethe Capitol building inWashington, D.C.,churches in Germany,and stained-glass windowsin Sweden. InLondon, acid rain hasforced workers to repairand replace so much ofWestminster Abbey that the structure is becominga mere copy of the original.Throughout the world, acid rain has weatheredmany structures more in the last 20 yearsthan in the 2,000 years before. This is one reasonsome steps have been taken in Europe and theUnited States to reduce emissions from theburning of fossil fuels. If these laws don’t work,many irreplaceable art treasures may be goneforever.Identify What are some famous monuments and buildings in theUnited States? Brainstorm a list with your class. Then choose amonument and, using your school’s media center or the Science Onlineaddress, learn more about it. Is acid rain affecting it in any way?For more information, visitred.msscience.com/time(t)Morton Beebe, SF/CORBIS, (b)Will & Deni McIntyre/Photo Researchers

Weathering and SoilFormation1. Weathering includes processes that breakdown rock.2. During mechanical weathering, physicalprocesses break rock into smaller pieces.3. During chemical weathering, the chemicalcomposition of rocks is changed.4. Soil evolves over time from weathered rock.Parent rock, topography, climate, andorganisms affect soil formation.Erosion of Earth’s Surface1. Erosion is the wearing away and removalof rock or sediment.2. Agents of erosion include gravity, ice, wind,and water. Downslope movement of a portionof the land’s surface is called massmovement.3. All agents of erosion move rock and sediment.When energy of motion decreases,sediment is deposited.4. Erosion and deposition determine theshape of the land.Copy and fill in the following table, which compares erosion and deposition by different agents.Erosion and DepositionErosional Agent Evidence of Erosion Evidence of DepositionGravityIceWindcirques, striations,U-shaped valleysmaterial piled at bottomof slopessand dunes, loessSurface Waterrills, gullies,stream valleysred.msscience.com/interactive_tutorCHAPTER STUDY GUIDE 335(l)Martin G. Miller/Visuals Unlimited, (r)James P. Rowan/DRK Photo

abrasion p. 328chemical weatheringp. 318creep p. 325deflation p. 328erosion p. 323mass movement p. 323mechanical weatheringp. 316runoff p. 329slump p. 325soil p. 320topography p. 320weathering p. 316Use each of the following pairs of terms in asentence.1. chemical weathering—mechanicalweathering2. erosion—weathering3. deflation—runoff4. mass movement—weathering5. soil—abrasion6. soil—erosion7. mass movement—mechanical weathering8. weathering—chemical weathering9. creep—slump10. topography—runoffChoose the word or phrase that best answers thequestion.11. Which of the following agents of erosionforms U-shaped valleys?A) gravity C) iceB) surface water D) wind12. In which of these places is chemicalweathering most rapid?A) desertsB) mountainsC) polar regionsD) tropical regions13. Which of the following forms when carbondioxide combines with water?A) calcium carbonateB) carbonic acidC) tannic acidD) dripstone14. Which process causes rocks to weather toa reddish color?A) oxidation C) carbon dioxideB) deflation D) frost action15. Which type of mass movement occurswhen sediments slowly move downhillbecause of freezing and thawing?A) creep C) slumpB) rock slide D) mudflow16. Which of the following helps form cirquesand U-shaped valleys?A) rill erosion C) deflationB) ice wedging D) till17. What is windblown, fine sediment called?A) till C) loessB) outwash D) delta18. Which of the following refers to water thatflows over Earth’s surface?A) runoff C) weatheringB) slump D) till19. Which of the following is an example ofchemical weathering?A) Plant roots grow in cracks in rock andbreak the rock apart.B) Freezing and thawing of water widenscracks in rocks.C) Wind blows sand into rock, scratchingthe rock.D) Oxygen causes iron-bearing minerals inrock to break down.20. Which one of the following erosionalagents creates desert pavement?A) wind C) waterB) gravity D) ice336 CHAPTER REVIEWred.msscience.com/vocabulary_puzzlemaker

21. Explain why mass movement is more commonafter a heavy rainfall.22. Describe how climate affects the developmentof soils.23. Explain how some mass movement could beprevented.24. Describe why chemical weathering wouldnot be rapid in Antarctica.25. Describe why caves form only in certaintypes of rock.26. Recognize Cause and Effect Explain how watercreates stream valleys.27. Form hypotheses about how deeply watercould erode and about how deeply glacierscould erode.28. Recognize Cause and Effect Explain how valleyglaciers create U-shaped valleys.29. Classify the following by the agent thatdeposits each: sand dune, delta, till, andloess.30. Concept Map Copy and complete the conceptmap showing the different types ofmass movements.31. Poster Use photographs from old magazinesto make a poster that illustrates differentkinds of weathering and erosion.Display your poster in your classroom.32. Model Use polystyrene, cardboard, and clayto make a model of a glacier. Include astream of meltwater leading away from theglacier. Use markers to label the areas oferosion and deposition. Show and labelareas where till and outwash sedimentscould be found. Display your model inyour classroom.Use the table below to answer questions 33–34.Loss and Formation of TopsoilYears SoilErodesTopsoil Lost (cm)Years to Re-createSoil Lost10 1 50015 1.520 2Do not write25 2.5in this book.30 340 4.5Soil particlesmove slowlydownhill.SlumpMass MovementWetsediment flowsdownhill.Rock slide33. Formation of Topsoil In a given region, it takes500 years to form 1 cm of topsoil. For the past20 years, the area has lost 1 cm of topsoil every10 years because of erosion. If erosion stopstoday, how long will it take to re-create the losttopsoil? How long will it take to re-create thetopsoil lost in 15, 25, and 30 years?34. Weather’s Affect In the 30th year, climatechanges and precipitation increases, causing anew erosion rate of 1.5 cm every 10 years. Howmany years will it now take to re-create thetopsoil lost at the end of 40 years?red.msscience.com/chapter_reviewCHAPTER REVIEW 337

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.Use the photo below to answer questions 7–8.1. Which is an example of mechanicalweathering?A. creepB. ice wedgingC. oxidationD. slump2. Which forms as a glacier moves into astream valley?A. cirqueB. outwashC. U-shaped valleyD. V-shaped valley3. Which factor in soil formation deals withthe slope of the land?A. climateB. parent rockC. timeD. topography4. Which is a mixture of weathered rock,organic matter, water, and air?A. humusB. organismsC. parent rockD. soil5. Which type of erosion occurs when a thinsheet of water flows downhill?A. creepB. gulley erosionC. runoffD. sheet erosion6. What causes potholes to form in roadways?A. creepB. ice wedgingC. oxidationD. slump7. Which form of mass movement is shownin this picture?A. creep C. rockslideB. mudflow D. slump8. Which agent of erosion causes this?A. gravity C. waterB. ice D. wind9. What form of mass movement occurswhen a pasty mix of water and sedimentmoves downhill?A. creep C. rockslideB. mudflow D. slump10. What type of erosion is similar to usingsandpaper to smooth the edges of wood?A. abrasionB. creepC. deflationD. runoffDouble Check For each question, double check that you arefilling in the correct bubble for the question number you areworking on.338 STANDARDIZED TEST PRACTICEJonathan Blair/CORBIS

Record your answers on the answers sheetprovided by your teacher or on a sheet of paper.Use the photo below to answer question 11.Record your answers on a sheet of paper.18. Compare and contrast chemical andmechanical weathering.19. How do freeze and thaw cycles contributeto both weathering and erosion?Use the photo below to answer question 20.11. How do lichens growing on rocks contributeto soil development?12. What is the difference between till andoutwash?Use the illustration below to answer question 13.Dunemovement20. Explain in detail what type of weatheringis taking place in this picture. Describethe type of environment where this weatheringwould take place the quickest.21. What types of glaciers are there and howdo they erode the land?Use to the photo below to answer question 22.13. Using the diagram, explain how a sanddune moves.14. What effect does climate have on the formationof humus?15. What type of mass movement causesproblems along the Southern Californiacoast? Why?16. What type of sediment is carried by thewind?17. Explain whether grasslands or forestsmake for better farmland.22. What type of erosion is pictured here?How can this type of erosion help to carryharmful chemicals that are deposited inthe soil to rivers, lakes and oceans?red.msscience.com/standardized_testSTANDARDIZED TEST PRACTICE 339(l)David Wrobel/Visuals Unlimited, (tr)Owen Franken/CORBIS, (br)David Muench/CORBIS