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EncyclopedicEntry

waterfallcascade

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Awaterfallisariverorotherbodyofwater'ssteepfalloverarockyledgeintoaplungepoolbelow.Waterfallsarealsocalledcascades.Theprocessoferosion,thewearingawayofearth,playsanimportantpartintheformationofwaterfalls.Waterfallsthemselvesalsocontributetoerosion.Often,waterfallsformasstreamsflowfromsoftrocktohardrock.Thishappensbothlaterally(asastreamflowsacrosstheearth)andvertically(asthestreamdropsinawaterfall).Inbothcases,thesoftrockerodes,leavingahardledgeoverwhichthestreamfalls.Afalllineistheimaginarylinealongwhichparallelriversplungeastheyflowfromuplandstolowlands.Manywaterfallsinanareahelpgeologistsandhydrologistsdeterminearegion'sfalllineandunderlyingrockstructure.Asastreamflows,itcarriessediment.Thesedimentcanbemicroscopicsilt,pebbles,orevenboulders.Sedimentcanerodestreambedsmadeofsoftrock,suchassandstoneorlimestone.Eventually,thestream'schannelcutssodeepintothestreambedthatonlyaharderrock,suchasgranite,remains.Waterfallsdevelopasthesegraniteformationsformcliffsandledges.Astream'svelocityincreasesasitnearsawaterfall,increasingtheamountoferosiontakingplace.Themovementofwateratthetopofawaterfallcaneroderockstobeveryflatandsmooth.Rushingwaterandsedimenttoppleoverthewaterfall,erodingtheplungepoolatthebase.Thecrashingflowofthewatermayalsocreatepowerfulwhirlpoolsthaterodetherockoftheplungepoolbeneaththem.Theresultingerosionatthebaseofawaterfallcanbeverydramatic,andcausethewaterfallto"recede."Theareabehindthewaterfalliswornaway,creatingahollow,cave-likestructurecalleda"rockshelter."Eventually,therockyledge(calledtheoutcropping)maytumbledown,sendingbouldersintothestreambedandplungepoolbelow.Thiscausesthewaterfallto"recede"manymetersupstream.Thewaterfallerosionprocessstartsagain,breakingdownthebouldersoftheformeroutcropping.Erosionisjustoneprocessthatcanformwaterfalls.Awaterfallmayformacrossafault,orcrackintheEarth’ssurface.Anearthquake,landslide,glacier,orvolcanomayalsodisruptstreambedsandhelpcreatewaterfalls.ClassifyingWaterfallsThereisnotastandardwaytoclassifywaterfalls.Somescientistsclassifywaterfallsbasedontheaveragevolumeofwaterinthewaterfall.AClass10waterfallusingthisscaleisIngaFalls,DemocraticRepublicofCongo,wheretheCongoRivertwistsinaseriesofrapids.TheestimatedvolumeofwaterdischargedfromIngaFallsis25,768cubicmeterspersecond(910,000cubicfeetpersecond).Anotherpopularwayofclassifyingwaterfallsisbywidth.OneofthewidestwaterfallsisKhonePhaphengFalls,Laos.Atthe

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KhonePhaphengFalls,theMekongRiverflowsthroughasuccessionofrelativelyshallowrapids.ThewidthoftheKhonePhaphengFallsisabout10,783meters(35,376feet).Waterfallsarealsoclassifiedbyheight.AngelFalls,theworld’stallestwaterfall,plummets979meters(3,212feet)intoaremotecanyoninarainforestinVenezuela.Thewater,fromtheGaujaRiver,oftendoesnotreachthebottom.Thefallissolong,andsosteep,thatairpressureisstrongeroftenthanthewaterpressureofthefalls.Thewateristurnedtomistbeforeitreachesthesmalltributarybelow.TypesofWaterfallsOneofthemostpopular,ifleastscientific,waystoclassifywaterfallsisbytype.Awaterfall'stypeissimplythewaythedescends.Mostwaterfallsfitmorethanonecategory.Ablockwaterfalldescendsfromawidestream.NiagaraFalls,intheU.S.andCanada,isablockwaterfallontheNiagaraRiver.Acascadeisawaterfallthatdescendsoveraseriesofrocksteps.MonkeyFalls,intheIndiraGandhiWildlifeSanctuaryandNationalParkinTamilNadu,India,isagentlyslopingcascade.Thewaterfallissafeenoughforchildrentoplayinthewater.Acataractisapowerful,evendangerous,waterfall.AmongthewidestandwildestofcataractsarethethunderingwatersoftheIguazuRiverontheborderbetweenBrazilandArgentina.Achuteisawaterfallinwhichthestreampassageisverynarrow,forcingwaterthroughatunusuallyhighpressure.ThreeChuteFallsisnamedforthethree"chutes"throughwhichtheTenayaCreekfallsinYosemiteNationalPark,California.Fanwaterfallsarenamedfortheirshape.Waterspreadsouthorizontallyasitdescends.VirginFallsisastrikingfanwaterfallonTofinoCreek,onVancouverIsland,BritishColumbia,Canada.Frozenwaterfallsarejustwhattheysoundlike.Foratleastpartoftheyear,thewaterfallfreezes.Mountaineersoftenclimbfrozenwaterfallsasachallengingtestoftheirskill.TheFangisasinglepillaroficeinVail,Coloradothatverticallyplungesmorethan30meters(100feet).Horsetailwaterfallsmaintaincontactwiththehardrockthatunderliesthem.ReichenbachFalls,afallontheReichenbachStreaminSwitzerland,isahorsetailwaterfallwherelegendarydetectiveSherlockHolmesallegedlyfelltohisdoom.Multi-stepwaterfallsareaseriesofconnectedwaterfalls,eachwiththeirownplungepool.Thebreathtaking"fallinglakes"ofPlitviceLakesNationalPark,Croatia,areaseriesofmulti-stepwaterfalls.Plungewaterfalls,unlikehorsetailfalls,losecontactwiththehardrock.ThetallestwaterfallinJapan,HannokiFalls,isaplungewaterfallthatstands497meters(1,640feet).HannokiFallsisseasonallyfedbysnowmeltfromtheTateyamaMountains.Punchbowlwaterfallsarecharacterizedbywidepoolsattheirbase.WailuaFallsisapunchbowlwaterfallontheislandofKauai,Hawaii.Althoughtheplungepoolistranquilandpopularforswimming,theareaaroundWailuaFallsitselfisdangerous.Thewaterflowingoversegmentedwaterfallsseparateasdistinctstreams.HugeoutcroppingsofhardrockseparatethestreamsofNigrettaFalls,asegmentedwaterfallinVictoria,Australia,beforetheymeetinalargeplungepool.CaseStudy:NiagaraFallsTheNiagaraRiverhastwofalls,oneintheU.S.stateofNewYorkandoneintheprovinceofOntario,Canada.Eachwaterfallislessthan60meters(200feet)tall,buttogethertheyaremorethanakilometer(.62miles)wide.Niagaraandmanyotherfallswithlargevolumesofwaterareusedtogeneratehydroelectricpower.AtremendousvolumeofwaterflowsoverNiagaraFalls,asmuchas5,525cubicmeters(195,000cubicfeet)persecond.Powerstationsupstreamfromthefallsconverthydroelectricenergyintoelectricityforresidentialandcommercialuse.

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VOCABULARY

airpressure noun forcepressedonanobjectbyairoratmosphere.

base noun bottomlayerofastructure.

canal noun artificialwaterway.

canyon noun deep,narrowvalleywithsteepsides.

cascade noun shallowwaterfalloverrocks.

channel noun deepestpartofashallowbodyofwater,oftenapassagewayforships.

classify verb toidentifyorarrangebyspecifictypeorcharacteristic.

commercial adjective havingtodowiththebuyingandsellingofgoodsandservices.

decrease verb tolower.

divert verb todirectawayfromafamiliarpath.

earthquake noun thesuddenshakingofEarth'scrustcausedbythereleaseofenergyalongfaultlinesorfromvolcanicactivity.

electricity noun setofphysicalphenomenaassociatedwiththepresenceandflowofelectriccharge.

elevation noun heightaboveorbelowsealevel.

engineer noun personwhoplansthebuildingofthings,suchasstructures(constructionengineer)orsubstances(chemicalengineer).

erosion noun actinwhichearthiswornaway,oftenbywater,wind,orice.

fallline noun imaginarylinealongwhichparallelriversplunge,orfall.

fault noun acrackintheEarth'scrustwheretherehasbeenmovement.

geologist noun personwhostudiesthephysicalformationsoftheEarth.

glacier noun massoficethatmovesslowlyoverland.

GreatLakes noun largestfreshwaterbodiesintheworld,locatedintheUnitedStatesandCanada.LakeHuron,LakeOntario,LakeMichigan,LakeErie,andLakeSuperiormakeuptheGreatLakes.

hydroelectricenergy

noun energygeneratedbymovingwaterconvertedtoelectricity.Alsoknownashydroelectricity.

hydroelectricpower

noun usableenergygeneratedbymovingwaterconvertedtoelectricity.

TheU.S.andCanadiangovernmentsmanagetheNiagaraRiversocarefullythatitispossibleforeithercountryto"turnoff"thefalls.Thisisdoneatnight,soasnottodisturbthetourismindustry,andthefallsareneveractuallyturnedoff,justsloweddown.Waterisdivertedtocanalsandreservoirs,andthedecreasedflowallowsengineerstocheckforerosionandotherdamageonthefalls.U.S.andCanadianauthoritiesalsoworktogethertoensureNiagaraFallsdoesn’tfreezeinthewinter,whichwouldthreatenpowerproduction.Becausewaterfallsarebarrierstonavigation,canalsaresometimesbuilttogetaroundthem.NiagaraFallspreventspassagebetweenLakeErieandLakeOntarioontheNiagaraRiver.Inthe19thcentury,theWellandCanalwasbuilttomakepassagebetweenthetwoGreatLakespossible.

Term PartofSpeech Definition

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hydrologist noun personwhostudiesthedistribution,circulation,andpropertiesofwater.

landslide noun thefallofrocks,soil,andothermaterialsfromamountain,hill,orslope.

mist noun cloudsatground-level,butwithgreatervisibilitythanfog.

mountaineer noun someonewhoclimbsmountains.

navigation noun artandscienceofdetermininganobject'sposition,course,anddistancetraveled.

outcropping noun layerofrockvisibleabovethesurfaceoftheEarth.

parallel adjective equaldistanceapart,andnevermeeting.

pebble noun verysmall,roundedrock.

plummet verb tofallsharply.

plungepool noun relativelydeeppoolofwaterbeneathawaterfall.

rainforest noun areaoftall,mostlyevergreentreesandahighamountofrainfall.

rapids noun areasoffast-flowingwaterinariverorstreamthatismakingaslightdescent.

recede verb togobackwardorwithdraw.

reservoir noun naturalorman-madelake.

sediment noun solidmaterialtransportedanddepositedbywater,ice,andwind.

silt noun smallsedimentparticles.

tourism noun theindustry(includingfood,hotels,andentertainment)oftravelingforpleasure.

tranquil adjective peacefulandcalm.

tributary noun streamthatfeeds,orflows,intoalargerstream.

velocity noun measurementoftherateanddirectionofchangeinthepositionofanobject.

volcano noun anopeningintheEarth'scrust,throughwhichlava,ash,andgaseserupt,andalsotheconebuiltbyeruptions.

volume noun spaceanobjectoccupies.

waterfall noun flowofwaterdescendingsteeplyoveracliff.Alsocalledacascade.

waterfall noun flowofwaterdescendingsteeplyoveracliff.Alsocalledacascade.

whirlpool noun llquidflowingquicklyinacircularmotion,pullingmaterialdownwardintoitscenter.

ForFurtherExploration

Articles&ProfilesNationalGeographicNews:"Lost"GiantWaterfallDiscoveredinCalifornia

InteractivesNationalGeographicKids:Puzzler—Waterfalls

WebsitesWorldWaterfallDatabase

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