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EROSION
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Erosionistheactinwhichearthiswornaway,oftenbywater,wind,orice.A
similarprocess,weathering,breaksdownordissolvesrock,weakeningitor
turningitintotinyfragments.Norockishardenoughtoresisttheforcesof
weatheringanderosion.Together,theyshapedthesharppeaksoftheHimalaya
MountainsinAsiaandsculptedthespectacularforestofrocktowersofBryce
Canyon,intheU.S.stateofUtah.
Theprocessoferosionmovesbitsofrockorsoilfromoneplacetoanother.
Mosterosionisperformedbywater,wind,orice(usuallyintheformofa
glacier).Theseforcescarrytherocksandsoilfromtheplaceswheretheywere
weathered.Ifwaterismuddy,itisasignthaterosionistakingplace.Thebrown
colorindicatesthatbitsofrockandsoilaresuspendedinthewaterandbeing
transportedfromoneplacetoanother.Thistransportedmaterialiscalled
sediment.
Whenwindorwaterslowsdown,oricemelts,sedimentisdepositedinanew
location.Asthesedimentbuildsup,itcreatesfertileland.Riverdeltasaremade
almostentirelyofsediment.Deltasedimentiserodedfromthebanksandbed
oftheriver.
ErosionbyWater
Movingwateristhemajoragentoferosion.Raincarriesawaybitsofsoiland
slowlywashesawayrockfragments.Rushingstreamsandriverswearaway
theirbanks,creatinglargerandlargervalleys.Inaspanofabout5million
years,theColoradoRivercutdeeperanddeeperintothelandinwhatisnow
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theU.S.stateofArizona.IteventuallyformedtheGrandCanyon,whichismore
than1,600meters(1mile)deepandasmuchas29kilometers(18miles)wide
insomeplaces.
Erosionbywaterchangestheshapeofcoastlines.Wavesconstantlycrash
againstshores.Theypoundrocksintopebblesandreducepebblestosand.
Watersometimestakessandawayfrombeaches.Thismovesthecoastline
fartherinland.
TheCapeHatterasLighthousewasbuiltin1870,ontheOuterBanks,aseriesof
islandsoffthecoastoftheU.S.stateofNorthCarolina.Atthetime,the
lighthousewasnearly1,000meters(3,300feet)fromtheocean.Overtime,
however,theoceanerodedmostofthebeachnearthelighthouse.By1999,the
surfendangeredthestructure.Manypeoplethoughtitwouldcollapseduringa
strongstorm.Thelighthousewasmoved880meters(2,900feet)inland.
Thebatteringofoceanwavesalsoerodesseasidecliffs.Itsometimesbores
holesthatformcaves.Whenwaterbreaksthroughthebackofthecave,it
createsanarch.Thecontinualpoundingofthewavescancausethetopofthe
archtofall,leavingnothingbutrockcolumns.Thesearecalledseastacks.Allof
thesefeaturesmakerockybeachesbeautiful,butalsodangerous.
ErosionbyWind
Windisalsoanagentoferosion.Itcarriesdust,sand,andvolcanicashfromone
placetoanother.Windcansometimesblowsandintotoweringdunes.Some
sanddunesintheBadainJaranareaoftheGobiDesertinChinareachmore
than400meters(1,300feet)high.
Indryareas,windblownsandblastsagainstrockwithtremendousforce,slowly
wearingawaythesoftrock.Italsopolishesrocksandcliffsuntiltheyare
smooth.
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WindisresponsibleforthedramaticarchesthatgiveArchesNationalPark,in
theU.S.stateofUtah,itsname.Windcanalsoerodematerialuntilnothing
remainsatall.Overmillionsofyears,windandwatererodedanentire
mountainrangeincentralAustralia.Uluru,alsoknownasAyersRock,istheonly
remnantofthosemountains.
ErosionbyIce
Icecanerodetheland.Infrigidareasandonsomemountaintops,glaciers
moveslowlydownhillandacrosstheland.Astheymove,theypickup
everythingintheirpath,fromtinygrainsofsandtohugeboulders.
Therockscarriedbyaglacierrubagainstthegroundbelow,erodingboththe
groundandtherocks.Glaciersgrinduprocksandscrapeawaythesoil.Moving
glaciersgougeoutbasinsandformsteep-sidedmountainvalleys.
SeveraltimesinEarth'shistory,vastglacierscoveredpartsoftheNorthern
Hemisphere.Theseglacialperiodsareknownasiceages.Glacierscarvedmuch
ofthenorthernNorthAmericanandEuropeanlandscape.Theyscouredthe
groundtoformthebottomofwhatarenowtheFingerLakesintheU.S.stateof
NewYork.Theyalsocarvedfjords,deepinletsalongthecoastofScandinavia.
Today,inplacessuchasGreenlandandAntarctica,glacierscontinuetoerode
theearth.Theseicesheets,sometimesmorethanamilethick,carryrocksand
otherdebrisdownhilltowardthesea.Erodedsedimentisoftenvisibleonand
aroundglaciers.Thismaterialiscalledmoraine.
ErosionandPeople
Erosionisanaturalprocess,buthumanactivitycanmakeithappenmore
quickly.Treesandplantsholdsoilinplace.Whenpeoplecutdownforestsor
plowupgrassesforagricultureordevelopment,thesoilwashesawayorblows
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awaymoreeasily.Landslidesbecomemorecommon.Wateralsorushesover
exposedsoilratherthansoakingintoit,causingflooding.
Erosioncontrolistheprocessofreducingerosionbywindandwater.Farmers
andengineersmustregularlypracticeerosioncontrol.Sometimes,engineers
simplyinstallstructurestophysicallypreventsoilfrombeingtransported.
Gabionsarehugewireframesthatholdbouldersinplace,forinstance.Gabions
areoftenplacednearcliffs.Thesecliffs,oftennearthecoast,havehomes,
businesses,andhighwaysnearthem.Whenerosionbywaterorwindthreatens
totumbletheboulderstowardbuildingsandcars,gabionsprotectlandowners
anddriversbyholdingtherocksinplace.
Erosioncontrolcanalsobedonebyphysicallychangingthelandscape.Living
shorelines,forexample,areaformoferosioncontrolforwetlandareas.Living
shorelinesareconstructedbyplacingnativeplants,stone,sand,andevenliving
organismssuchasoystersalongwetlandcoasts.Theseplantshelpanchorthe
soiltothearea,preventingerosion.Bysecuringtheland,livingshorelines
establishanaturalhabitat.Theyprotectcoastlinesfrompowerfulstormsurges
aswellaserosion.
Globalwarming,thelatestincreaseintemperaturearoundtheworld,is
speedingerosion.Thechangeinclimatehasbeenlinkedtomorefrequentand
moreseverestorms.Stormsurgesfollowinghurricanesandtyphoonsthreaten
toerodemilesofcoastlineandcoastalhabitat.Thesecoastalareashave
homes,businesses,andeconomicallyimportantindustries,suchasfisheries.
Theriseintemperatureisalsoquicklymeltingglaciers.Thisiscausingthesea
leveltorisefasterthanorganismscanadapttoit.Therisingseaerodes
beachesmorequickly.IntheChesapeakeBayareaintheeasternUnitedStates,
itisestimatedthatariseinsealevelof8to10centimeters(3to4inches)will
causeenougherosiontothreatenbuildings,sewersystems,roads,andtunnels.
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Vocabulary
Term
Partof
Definition
Speech
adapt
verb
agriculture
noun
anchor
verb
toholdfirmlyinplace.
arch
noun
shapethatlookslikeanupside-down"U."
basin
noun
batter
verb
bioerosion
noun
bore
verb
todrillortunnelintosomething.
boulder
noun
largerock.
Bryce
Canyon
cave
noun
noun
toadjusttonewsurroundingsoranewsituation.
theartandscienceofcultivatingthelandforgrowing
crops(farming)orraisinglivestock(ranching).
adipordepressioninthesurfaceofthelandorocean
floor.
tobeatandcausedamage.
theprocessinwhichalivingorganismwearsawayatrock
oranotherhardsubstance.
largerockformations(notacanyon)intheU.S.stateof
Utah.
undergroundchamberthatopenstothesurface.Cave
entrancescanbeonlandorinwater.
large,shallowestuaryoftheSusquehannaandother
Chesapeake
Bay
riversthatflowthroughtheU.S.statesofMaryland,
noun
Virginia,WestVirginia,Delaware,Pennsylvania,andNew
YorkandthecapitalofWashington,D.C.,beforeemptying
intheAtlanticOcean.
cliff
noun
climate
noun
coastline
noun
steepwallofrock,earth,orice.
allweatherconditionsforagivenlocationoveraperiodof
time.
outerboundaryofashore.
remainsofsomethingbrokenordestroyed;waste,or
debris
noun
garbage.
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Term
Partof
Definition
Speech
delta
noun
deposit
verb
theflat,low-lyingplainthatsometimesformsatthemouth
ofariverfromdepositsofsediments.
toplaceordeliveraniteminadifferentareathanit
originated.
developmentnoun
growth,orchangingfromoneconditiontoanother.
dissolve
verb
tobreakupordisintegrate.
dust
noun
earth
noun
economic
adjectivehavingtodowithmoney.
endanger
verb
tiny,dryparticlesofmaterialsolidenoughforwindto
carry.
soilordirt.
toputatrisk.
personwhoplansthebuildingofthings,suchasstructures
engineer
noun
(constructionengineer)orsubstances(chemical
engineer).
erode
verb
erosion
noun
erosion
control
noun
towearaway.
actinwhichearthiswornaway,oftenbywater,wind,or
ice.
processofpreventingorreducingerosionbywindand
water.
farmer
noun
fertile
adjectiveabletoproducecropsorsustainagriculture.
FingerLakesnoun
personwhocultivateslandandraisescrops.
seriesofthin,deeplakesintheU.S.stateofNewYork.
industryoroccupationofharvestingfish,eitherinthewild
fishery
noun
fjord
noun
long,narrowoceaninletbetweensteepslopes.
flood
noun
overflowofabodyofwaterontoland.
forest
noun
ecosystemfilledwithtreesandunderbrush.
frequent
adjectiveoften.
gabion
noun
orthroughaquaculture.
wireframefilledwithrock.
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Term
glacial
period
glacier
global
warming
Partof
Definition
Speech
noun
noun
noun
timeoflong-termloweringoftemperaturesonEarth.Also
knownasaniceage.
massoficethatmovesslowlyoverland.
increaseintheaveragetemperatureoftheEarth'sairand
oceans.
GobiDesert noun
largedesertinChinaandMongolia.
gouge
handtoolwithapartlycurvedblade,usedforcarving.
Grand
Canyon
noun
noun
largegorgemadebytheColoradoRiverintheU.S.state
ofArizona.
environmentwhereanorganismlivesthroughouttheyear
habitat
noun
highway
noun
largepublicroad.
noun
mountainrangebetweenIndiaandNepal.
Himalaya
Mountains
orforshorterperiodsoftime.
tropicalstormwithwindspeedsofatleast119kilometers
hurricane
noun
(74miles)perhour.Hurricanesarethesamethingas
typhoons,butusuallylocatedintheAtlanticOceanregion.
ice
noun
waterinitssolidform.
longperiodofcoldclimatewhereglacierscoverlarge
iceage
noun
partsoftheEarth.Thelasticeagepeakedabout20,000
yearsago.Alsocalledglacialage.
icesheet
noun
thicklayerofglacialicethatcoversalargeareaofland.
indicate
verb
todisplayorshow.
inlet
noun
smallindentationinashoreline.
island
noun
bodyoflandsurroundedbywater.
landslide
noun
lighthouse
noun
thefallofrocks,soil,andothermaterialsfroma
mountain,hill,orslope.
structuredisplayinglarge,brightlightstowarnandhelp
shipsnavigatecoastalwaters.
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Term
living
shoreline
moraine
mountain
range
Northern
Hemisphere
Partof
Definition
Speech
noun
noun
methodofcreatingcoastallandbyusingstonesand
marinegrassestotrapsoil,sand,andmud.
material,suchasearth,sand,andgravel,transportedbya
glacier.
noun
seriesorchainofmountainsthatareclosetogether.
noun
halfoftheEarthbetweentheNorthPoleandtheEquator.
OuterBanks noun
barrierislandsoffthecoastoftheU.S.stateofNorth
Carolina.
oyster
noun
typeofmarineanimal(mollusk).
peak
noun
theverytop.
noun,
toolusedforcutting,lifting,andturningthesoilin
verb
preparationforplanting.
polish
verb
tomakesmoothandshinybyrubbing.
reduce
verb
tolowerorlessen.
remnant
noun
somethingthatisleftover.
rock
noun
naturalsubstancecomposedofsolidmineralmatter.
sand
noun
small,loosegrainsofdisintegratedrocks.
sanddune
noun
moundofsandcreatedbythewind.
plow
Scandinavia noun
scour
verb
sealevel
noun
seastack
noun
sediment
noun
sewer
noun
regionandnameforsomecountriesinNorthernEurope:
Iceland,Norway,Sweden,Finland,andDenmark.
torubharshly,oftentopolish.
baselevelformeasuringelevations.Sealevelis
determinedbymeasurementstakenovera19-yearcycle.
column-shapedrockformationcreatedbywaveseroding
partsofcoastalcliffs.
solidmaterialtransportedanddepositedbywater,ice,
andwind.
passagewayorholdingtankforliquidwaste.
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Term
Partof
Definition
Speech
shore
noun
coast.
soil
noun
toplayeroftheEarth'ssurfacewhereplantscangrow.
spectacular adjectivedramaticandimpressive.
storm
noun
stormsurge noun
severeweatherindicatingadisturbedstateofthe
atmosphereresultingfromupliftedair.
abnormalriseinsealevelaccompanyingahurricaneor
otherintensestorm.Alsocalledastormtide.
stream
noun
bodyofflowingfluid.
surf
noun
wavesastheybreakontheshoreorreef.
suspend
verb
totemporarilystopanactivity.
temperature noun
degreeofhotnessorcoldnessmeasuredbya
thermometerwithanumericalscale.
tremendous adjectiveverylargeorimportant.
tropicalstormwithwindspeedsofatleast74miles(119
typhoon
noun
kilometers)perhour.Typhoonsarethesamethingas
hurricanes,butusuallylocatedinthePacificorIndian
Oceanregion.
largesandstonerockformationincentralAustralia.Also
Uluru
noun
valley
noun
vast
adjectivehugeandspreadout.
calledAyersRock.
depressionintheEarthbetweenhills.
volcanicash noun
fragmentsoflavalessthan2millimetersacross.
water
noun
chemicalcompoundthatisnecessaryforallformsoflife.
wave
noun
movingswellonthesurfaceofwater.
weathering noun
wetland
noun
thebreakingdownordissolvingoftheEarth'ssurface
rocksandminerals.
areaoflandcoveredbyshallowwaterorsaturatedby
water.
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Term
Partof
Definition
Speech
movementofair(fromahighpressurezonetoalow
wind
noun
pressurezone)causedbytheunevenheatingoftheEarth
bythesun.
Articles&Profiles
AssociationofBayAreaGovernments:WhatYouCanDotoControlErosion
andProtectYourProperty
Audio&Video
NationalGeographicVideo:AlaskaCoastErodingFast
Websites
NationalGeographicScience:ErosionandWeathering
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