Aridlandformdevelopment
3.1.2.3Hotdesertsystemsandlandscapes
Whatyouneedtoknow
Originanddevelopmentoflandformsofmidandlowlatitudedeserts–formedbyaeolian
andwaterprocesses
Therelationshipbetweenprocess,time,landformsandlandscapesinmidandlowlatitude
desertsettings
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Originanddevelopmentoflandformsofmidandlowlatitudedeserts
Thehugescaleofdeserts,thelackofsurfacevegetationcloakingthelandscapeandtheremoval
offinesedimentsbytheactionofwindandwatercanproducespectaculardesertlandforms.
Aeolian(wind)erosionalfeatures
• Deflationhollows:Surfacedepressions,knownasdeflationhollows,haveformedin
someoftheworld’slargestdesertsbytheerosionalprocessofdeflation.Dewcollectsin
low-lyingbasins,providinganinputofmoisture.Thesurfacematerialisthenbroken
downbychemicalweatheringandtransportedawayonthewind.Someofthedeflation
hollowsintheSaharaDesertarehundredsofkilometreswide.ThelargestistheQattara
DepressioninEgyptwhich,atitsdeepestpoint,is134metresbelowsealevel.The
AmericanMid-WestDustBowlofthe1930swasformedasaconsequenceofdeflation,
followingaseveredroughtthatmadethesoildry,friableandpronetowinderosion.In
theexampleoferosionintheAmericanMid-West,thedynamicequilibrium(the
tendencytowardsanaturalstateofbalance)wasupsetbyanextremeevent,inthiscase
drought,butitcouldeasilybeastormorfloods.Humanactivitycanalsocause
disruptiontothedynamicequilibrium,suchasbymodifyingthedrainagebasin
• Desertpavements:Coveringhugeareas,desertpavementsor‘reg’areflat,stony
surfacesthatresembleacobbledstreet.Anysilt-sizedorsand-sizedparticleshavebeen
blownandtransportedelsewhere.Thedesertsurfacerepresentsalltheparticlesthat
aretoolargetobeliftedbythewindandcanbeameasureofwindstrength(thelarger
thedominantsedimentleftbehind–thestrongerthewind).
• Ventifacts:Individualrocksandbouldersareoftenthefocusforwinderosion.Sandin
suspensioncausesabrasionandpittingonthesidefacingtheprevailingwind.Abrasion
cancompletelysmoothonesideofarockandproduceirregularsandblastedshapes.
• Yardangs:Extensiveridgesofrockknownasyardangs,separatedbygrooves(troughs)
canforminalignmenttotheprevailingwinddirection.Theseridgesareusuallythreeto
fourtimeslongerthantheyarewide.Strongwindsblowinginonedirectionand
carryingsandinsuspensionerodethedesertsurfacebyabrasion.Softerrockserode
fasterthanharderrocks,soridgesofmoreresistantrocksremainupstanding.Inparts
oftheSaharan,ArabianandAtacamaDeserts,yardangsarelargeenoughtobevisibleon
satelliteimagery.
• Zeugen:thisisanotherlandformsculptedbywinderosion.Theyarelongtabular
(block-shaped)massesofresistantrockseparatedbytrenchesandareformedinareas
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Aridlandformdevelopment
3.1.2.3Hotdesertsystemsandlandscapes
wheremoreresistantrockoverlieslessresistantrocks.Theoverlyingrocksare
weatheredandthewindcutsverticallythroughthecapexposingtheunderlyingsofter
rock,whichisthenerodedmorerapidly.Zeugenscanbeanywherebetweenfiveand30
metresinheight.
•
Rockpedestals:Thesemushroom-shapedrocksformasaresultofsandblasting.Sand
particlesskipacrossthedesertsurfaceblownbystrongwindsandabradeanythingin
theirpath.Sandblastingismosteffectivewithinthefirst1.5metresoftheground
surfaceandthismeansthatthereissignificantundercuttingofthebaseofverticalrocks.
Continuederosionofthe‘stalk’canleadtotheeventualcollapseofthepedestal.
SpectacularrockpedestalsareseeninUtah,USAandtheWhiteDesertinEgypt.
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Aeoliandepositionalfeatures
Whensandgrainstransportedbysaltationaredeposited,theyformsanddunesasthewind
slowsdown.Windcanslowforanumberofreasons,butitisusuallyvegetation,rocksorother
sanddunescreatinganobstacle.Sanddunesforminanumberofshapesandlayoutsdependent
uponanumberoffactors:
• Thedirectionandspeedofthewind
• Thequantityofsandbeingtransported
• Thenatureofthedesertsurface
• Thepresenceofvegetation
• Erg:Alargeareaofsanddunesisknownasanerg(sandsea).Thesefeaturescanstretch
forhundredsofkilometresandcoverapproximatelyonequarterofallaridregions.Ergs
aremainlyconfinedtotheArabianandSaharaDeserts.Sandseasareanaptnamefora
largeareaofsanddunesduetothewaythatsanddunesappearlikeaslow-moving
waveastheymigratewiththewind.Fivebasicduneshapeshavebeenrecognised:
crescentic,linear,star,domeandparabolic.
• Barchandunes:Thebarchanisacrescent-shapeddunethatcanreach30mhighandis
movedbythewind.Saltationandsurfacecreeptakeplaceonthegentleupwind-facing
slopeofthedune(stossface)asthewindpushesmaterialupslope.Sedimentthen
continuallyavalanchesovertheridgeanddownthesteeperlee(slipface)ofthesand
dune,movingtheentiresandduneforwardatarateofupto30m/yr.Swirlingwind
currents(eddies)helptokeeptheleeslopesteep.Thehorns(edgesofthedune)move
fasterthanthecentreoftheduneasthereislesssandtomove.Thebarchandunebelow
isactuallyonMars!
• Seifdunes:thesearelongitudinaldunes(namedafteranArabcurvedsword)thatare
longridgesofsandwhichformparalleltotheprevailingwind.Theyaremuchlargerand
morecommonthanbarchandunes.Seif(linear)dunescanreach200minheightand
over100kminlength.Theyformfromlinkedbarchanduneswhenatemporary–but
repeated-changeinwinddirectionoccurs.Thiscausesoneofthehornsor‘arms’ofa
barchandunetoelongateandmergewithitsneighbouringdunetoformaseriesof
connecteddunes.ThesedunesaredominantinSouthEastLibyaandSouthWestAlgeria.
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Aridlandformdevelopment
3.1.2.3Hotdesertsystemsandlandscapes
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ImageofaMartianbarchandunetakenbytheMarsReconnaissanceOrbiter:NASA/JPL/UniofArizona
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Water(fluvial)landforms
Althoughstormsareinfrequentindesertareas,torrentialraincanbeveryerosivealteringthe
landscapedramatically,bringingsedimentdownfromdesertmountains,reshapingriverbeds
anddepositingdebrisinalluvialfans,bahadasandchotts.Theseareclassedasfluvialprocesses
andlandformsasdistinctfromaeolianor‘windblown’processesandfeatures.
Erosionalfeatures
• Inselbergs:Meaning‘islandhill’(German),inselbergsareisolatedsteep-sidedhills
includingmesasandbuttesthatareremnantsoftheerosionprocessuponextensivedesert
surfacesleavingmassesofmoreresistantrockaslegacyfeaturesinaloweredplain.Mesas
areplateau-likemountainsandbuttesareisolatedpillar-likeformations.Thereisgreat
debateabouttheconditionsunderwhichinselbergsform.Manygeomorphologistsnow
believethattheyarerelictuplandsofpastclimaticconditionswhenrainfallwashigherand
hadmuchmorepowertoerodethesofterrocksurroundinginselbergs,bywatererosion.
Uluru(AyersRock)isaninselberginAustralia.
• Wadis:Dryrivervalleysknownaswadisaredryformostoftheyearandonlyfillwith
waterflowinginephemeralstreamsaftertorrentialrain.Wadiscandevelopintodeep
ravinesandgorgesiftheyarerepeatedlyerodedbyfast-flowingtorrentsofwater.
Depositionalfeatures
Themaindepositionalfeaturescreatedbyflowingwaterindesertlandscapescanbefound
withinintermountainbasinsordesertpediment.
• Pediments:thesearegentleslopingterrainlocatedatthefootofdesertmountainranges
withalowslopeangle(between1°and7°)consistingeitherofsolidbaserock,depositional
accretions,oramixtureofthetwo.Theyrepresentthejunctionbetweenazoneofsteep
slopesanderosionalprocesses(uplands)andflat,depositionallowlands.Theyareformed
bytheabrasionofrockbythesedimentcarriedinsheetfloodsandareusuallycoveredina
thinlayerofsedimentrepresentingtheremainsofthelastflood.
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Aridlandformdevelopment
3.1.2.3Hotdesertsystemsandlandscapes
•
Bahadas(Bajadas–Spanishfor‘slope’):Whereanumberofparallelwadisconvergeata
mountainfrontincloseproximity,anumberofalluvialfanscoalescewiththoseadjacenton
eitherside,formingabahada/bajada.Thesebahadascancoverupmountainpediments,or
formatthefootofthemwherethegradientbecomesalmostflat.
Chotts:Chotts(NorthAfrica),sabkhahs(ArabianPeninsula)andplayas(NorthAmerica)or
pan(Australia)areallnamesforsaltlakesortheirevaporateddeposits.Thesefeaturesare
verycommonindesertsandhaveanumberofcommoncharacteristics:
§ Theyfeatureatthelowpointsofthedesertlandscape
§ Theyareusuallyveryflat
§ Theyhavenooutlettothesea
§ Ephemeralwatercollectsinthemafterheavyrain
§ Evaporationleadstotheformationofsaltpansorthickcrustsofsaltand
otherevaporatedeposits
§ Vegetationissparseduetothesaltleftbehindafterevaporationofthe
ephemeralwater
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Alluvialfans:thesearedelta-likedepositionallandformsthatdevelopwhereanephemeral
streamrunsoverabreakofslopetoashallowergradient,causingenergylossandthe
consequentialdepositionofthesedimentcarried.Thedepositedsedimentspreadsoutinto
afanshape,theheaviestbeingdroppedfirst.Alluvialfanscanbeanywherefrom20kmin
lengthand300minthickness.Thepedimentoftenformsthebreakinslopeuponwhichthe
depositionofdiscrete(individual)alluvialfanstakesplace.
ChottEchCherguialargeendorheicsaltlakeinSaïdaProvince,Algeriaandalthough
vegetationissparseithasbeendesignatedaRamsarwetlandofinternational
importanceforanumberofthreatenedandvulnerableanimalandplantspecies.
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Therelationshipbetweenprocess,time,landformsandlandscapesinmidandlow
latitudedesertsettings:characteristicdesertlandscapes.
Manyofourpresent-daydesertswereoncemuchwetter,fertilegrasslandsandforestsinthe
past.SomeoftheevidenceforthisincludesstoresofgroundwaterundertheSahara,oldsoil
horizonsandrelictlandformssuchasmesasandbuttesinUtah,USA.8,000yearsagothe
northernhemispherehadawetterclimate,monsoonsintensifiedandtheSaharaexperienced
humidconditions.DuringtheHoloceneClimateOptimum(9000-4000BC),Lake‘Mega-Chad’
washundredsofkilometreswidewithpeoplesettledonitsshores.InSudan,WadiHowar,a
oncemightyriver,sustainedfishandcrocodilesaswellasagricultureandhumansettlement
andinsouth-eastAlgeria,rockpaintingsshowsavannahanimalssuchaselephantsandzebus
(cattle).
ItisthoughtthatthedryingofSaharafromsavannahtodesertbeganaround5,500yearsago
andwascausedbyashiftintheEarth’sorbit.Thismeansthecurrentdesertlandscapeisan
accumulationofatime-seriesoflandformsandlandscapes,someofwhichwereformedunder
pastclimaticconditionsbutarestillevident,somethathavebeendevelopingoverrecent
millennia(thousandsofyears)butarepersistent,someoverthelastcentury,andothersthat
arequiteshort-livedfeaturesbutthatareinexistenceduringcontemporaryconditions.
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TheKavirDesertandthedevelopmentofhotdesertlandforms
Specificationtopic:Aridlandscapeandlandformdevelopment3.1.2.3
Casestudy:TheKavirDesert,Iran.
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TheKavirDesert(Dasht-eKavirliterally‘desertofsaltmarsh’),alsoknownastheGreatSalt
Desert,islocatedontheIranianplateauinabasinsoutheastoftheElburzMountainsand
Tehran.ItisthelargestdesertinIran,approximately800kmwideby320kminlengthand
stretchesfromtheAlborzmountainrangeinthenorth-westtotheDasht-eLutdesertinthe
south-east.Themainfeaturesofthedesertarehamadas(pebblysteppes),kavirs(salt
deserts)andsanddunes.
Saltdeposits
TensofmillionsofyearsagothisareawascoveredinasalineoceancalledtheParatethys
Sea,whichdriedupandleftalayerofsaltoversixkilometresthick.Inmorerecenttimes
layersofmudburiedthissalt.Assalthasalowerdensitythanmud,itpushedthroughthe
mudandformedsaltdomesordiapirs.Thesedomeshavealsobeensqueezedandfoldedby
recenttectonicupliftandthetopsofthesedomeshavebeenwornawaybywindandrain,
leavingthelayersexposedincross-section.NamakLakehasasurfaceareaofabout1800
km²,butwateronlycovers1km²andisonemetreatitsdeepest.Therestofitisdryandthe
salthasformedintosaltpolygons(hexagonaltooctagonalshapes).Theunderlyingmudand
saltlayerfindsitswaytothesurfaceunderhighpressureandtemperaturesandthe
polygonsform.Thelakeisaremnantofalargesalineocean,whichleftLakeUrmiaandthe
CaspianSeaasrelictfeaturesfurthertothenorth.
Saltmarshesandcrusts
Thedesertisincrediblyaridandhighevaporationrateshaveresultedintheformationof
manysaltlakes.Saltcrusts(duricrust)haveformedoverthesaltmarshesandtheycanbe
particularlydangerousifpeopletrytotravelacrossthem.Thelargestofthesaltmarshesis
KavirBuzurganditisover320kminlength.Withhazardoussaltmarshes,faultlinesthat
runthroughthisareaandextremelyhottemperaturesfewpeoplesettlehere.Althougha
fewanimalherderscalledtheYazd,livearoundtheoasesofMesr,FarahzadandAmirabad.
Althoughthetemperaturesregularlyreach50°C,frequentheavystormscausemany
erosionallandformsinthesedimentaryrocksoftheflathilltops.Thisresultsinthe
formationofshallow,widewadis,whereephemeralstreamsoccasionallyflow,inbetween
thesaltmarshes.
Sanddunes
Inthenorthernpartofthedesertliesanddunesandshiftingsands.Barchandunesinsingle
andcomplexformscanbefoundaroundMaranjabcaravanseraiandmayreachheightsof
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TheKavirDesertandthedevelopmentofhotdesertlandforms
5.8metres.WithintheKavirnationalparkregion,sword-shapedseifduneshaveformed
alongsidespectacularwind-blownripplemarks.Sanddunesmostlyconsistofparticlesof
quartz,feldsparandsomeotherminerals.Inbetweenduneswherethewatertableishigh
andplantsareabletogrow,sandgetstrappedinthevegetationandlowhillsgrow.These
nebkhasarearound1.8–3.0metresinheight
Desertpavements
Theseareformedbythewinderosionofsandandsilt,leavingbehindangularpebble-sized
rocksontheslopesofSiahKuh(BlackMountain).Sometimestheyhaveshiny,glossy,
opaqueandothersmoothsurfacesaccordingtohowhardtheyare.
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Examstylequestions
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1. Accountforthewiderangeoflandformsfoundinmidandlowlatitudedeserts. (6marks)
2. Examinetherelationshipbetweenprocess,time,landformsandlandscapesinmidandlow
latitudedeserts.(20marks)
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TheKavirDesertandthedevelopmentofhotdesertlandforms
1. Accountforthewiderangeoflandformsfoundinmidandlowlatitudedeserts.
(6marks)
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Responsesshouldcoveranumberofdifferentprocessesandtheresultantlandforms/landscapes.
Everydesertlandformorlandscapedoesnotneedtobecovered,butenoughincludedtoshowa
breadthofunderstandingaboutchemicalandmechanicalweatheringprocessesaswellaswind
(abrasionanddeflation)andwatererosion.
• Thereareawiderangeoflandscapesinmidandlowlatitudedeserts.Responsescould
includeadiscussionaboutanyofthefollowing-desertuplandsandmountains,desert
plateaus,stonydeserts,desertfloodplains/wadis,desertlakebasinsandsandydeserts
• Thereareawiderangeoflandformsinmidandlowlatitudedesertsbecauseofthewide
rangeofprocesses(waterandwinderosion,weathering,transportationanddeposition)that
takeplaceacrossanumberofdifferentlandscapes.
• Originanddevelopmentoflandformscanincludeaeolianfeaturessuchasdeflationhollows,
desertpavements,ventifacts,yardangs,zeugen,barchansandseifdunesandwaterfeatures
suchaswadis,bahadas,pediments,playas,inselbergs.
• Thereareawiderangeofprocesseswhichshapethedesertincludingweathering,windand
watererosion.
• Inaddition,theclimate,soilsandvegetationallinfluencethephysicalprocessestakingplace
inadesertandhelpshapethelandscapeandlandforms.
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TheKavirDesertandthedevelopmentofhotdesertlandforms
2. Examinetherelationshipbetweenprocess,time,landformsandlandscapesinmidandlow
latitudedeserts.(20marks)
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Therearecomplexrelationshipsbetweenprocess,time,landformsandlandscapes.Responses
shoulddevelopsomeoftheinter-relationships(linksbetweentwoormorephenomena,suchthat
changingoneleadstochangeintheother)betweenprocess,time,landformsandlandscapesinmid
andlowlatitudedeserts.Answersshouldincludethefollowing:
• Theconceptsoflandformandlandscapeandhowrelatedlandformscombinetoform
characteristiclandscapes.Thiscanincludesanddunesandothersandfeaturesdeveloped
undercontemporaryconditions.
• Wherelandformandlandscapefeaturesarenotrelatedtheywereprobablyformedunder
differentconditionsforexamplefindingsaltdomesnexttodesertpavements.
• Therelationshipbetweenlandforms,landscapesandlocation(midandlowlatitude)should
linktohigh-pressuresystems,lowrainfallandtheformationofdesertlandforms.However,
asthelandscapeisapalimpsest(superimpositionoffeaturesdevelopedatdifferentphases
overagiventimescale)ofpastlandformsandcurrentprocesses,thereisoftenamixtureof
landformsformedinrecentaridconditionsandthoseofthepast.Pastconditionscouldbe
warmer,wetter(givingrisetofossilaquiferreservesofwater)oritcouldhaveevenbeena
coastalormarineenvironment.
• Certainrelictlandformscouldhaveonlyformedunderdifferentclimaticconditions.For
example,saltdomesofover6kmmusthavedevelopedwhensealevelswererisingand
fallingandtheareawasunderwater.Saltmarsheswouldhavetakenmillionsofyearsto
formandwouldhaverequiredconditionstobewarm,sothatevaporationcouldmakethe
waterhighlysalineforthesalttobedeposited.
• Basedonthepresent-dayclimatedata,thereisalinkofdesertpedimentstoancienthumid
phases,whichprovidedhigh-energyrunofffortheformationoftheselandformsandwere
associatedwitherosionalfeaturesundermorehumidandcolderclimateduringthelast
glacialperiod.
• Foldingisevidenceoftectonicuplift,andsignificantancientearthmovementwererequired
totiltrockstratatoaverticalorientationforyardangstobecurrentlydevelopingstill.
• Deepravinesandwadisareoftenevidenceofapastenvironmentthatwaswetterand
experiencedmorerainfallwhereriversflowedforlongerandhadmoreerosivepower.
• Desertplainsandaeoliandunesaretherelatedproductsofcontemporaryclimate,suchas
smallerbarchansanddunes,havingbeenerodedandtransportedmorerecently.
• Differentpastconditionswouldhavegivenrisetodifferentprocesses,whichwouldhave
resultedindistinctivelandformsforthetime.Thesemaynowberelictfeatures.
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HotDeserts:Aridlandscapeandlandformdevelopment3.1.2.3
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Q1
TrueorFalse?
A
Desertpavements(reg)areflat,stonysurfacesmadeofstonestooheavytolift
B
Yardangsareformedwheremoreresistantrockoverlieslessresistantrocks.
C
Rockpedestalsaresandblastedlandforms,withwidestalkssupportingthem.
D
Theslopeontheleewardsideofabarchanduneisthesteepestside
E
Seifdunescanbeover200mhighandformatrightanglestotheprevailingwind Q2
Matchthecorrecttermtothecorrecterosionallandform
A
Isolatedsteep-sidedrelicthillsthatriseupfrompedimentse.g.Uluru,Australia B
Plateau-likemountainwheretheflatsurfaceiswiderthanthemountainistall
C
Isolatedpillar-likehills,tallerinheightthanthesurfaceiswide
D
Dryrivervalleysformostoftheyear,onlyfillingwithwateraftertorrentialrain E
Gentleslopingdesertplainsatthefootofmountainranges
Selectfrom:MesasWadisPedimentsButtesInselberg
Q3
Allocatethecorrectdescriptionalternativetothemostappropriatesanddunetype
Barchandunes
Seifdunes
Travelatarateofupto10mperyear/Travelatarateofupto30mperyear
Linearinshape/CrescentshapedCanreach30minheight/Canreach200minheight
Hornshapedends/Tuningforkshaped
Canreach100kminlength/Canreach400minlength
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HotDeserts:Aridlandscapeandlandformdevelopment3.1.2.3
Q4
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Comparingtwodistinctivedesertlandscapes,howmighteachofthevariables
affectthedevelopmentofthenamedfeatures
Thedevelopment Hotterthanusualtemperature:
ofchotts
Unusuallywetyear:
Theformationof Frequentrainfall:
alluvialfans
Largeamountofstreamsediment:
Q5 Explainallthewaysapreviouslywetterclimatemaystillbeinfluencingkeyfeaturesina
contemporarydesertlandscape
Apreviouslywetterclimatemaystillbeinfluencingkeyfeaturesinacontemporarydesert
landscapeincluding:
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HotDeserts:Aridlandscapeandlandformdevelopment3.1.2.3
ANSWERS
Q1
A
B
C
D
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TrueorFalse?
Desertpavements(reg)areflat,stonysurfacesmadeofstonestooheavytolift
Yardangsareformedwheremoreresistantrockoverlieslessresistantrocks.
Verticalalternatelayersofrockalongwhichwinderodessofterbandsfaster
Rockpedestalsaresandblastedlandforms,withwidestalkssupportingthem.
Narrowstalksarereducedduetoaeolianabrasionwithwiderplatformsabove
Theslopeontheleewardsideofabarchanduneisthesteepestside
Seifdunescanbeover200mhighandformatrightanglestotheprevailingwind
Formparalleltotheprevailingwindbutwherealternativewinddirectionoccurs
True
False
False
True
False
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Q2
Matchthecorrecttermtothecorrecterosionallandform
A
Isolatedsteep-sidedrelicthillsthatriseupfrompedimentse.g.Uluru,Australia Inselberg
B
Plateau-likemountainwheretheflatsurfaceiswiderthanthemountainistall
Mesas
C
Isolatedpillar-likehills,tallerinheightthanthesurfaceiswide
Buttes
D
Dryrivervalleysformostoftheyear,onlyfillingwithwateraftertorrentialrain Wadis
E
Gentleslopingdesertplainsatthefootofmountainranges
Pediments
Selectfrom:MesasWadisPedimentsButtesInselberg
Q3
Allocatethecorrectdescriptionalternativetothemostappropriatesanddunetype
Barchandunes
Seifdunes
Crescentshaped
Linearinshape
Canreach30minheight
Canreach200minheight
Canreach400minlength
Canreach100kminlength
Travelatarateofupto30mperyear
Travelatarateofupto10mperyear
Hornshapedends
Tuningforkshaped
Travelatarateofupto10mperyear/Travelatarateofupto30mperyear
Linearinshape/CrescentshapedCanreach30minheight/Canreach200minheight
Hornshapedends/Tuningforkshaped
Canreach100kminlength/Canreach400minlength
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HotDeserts:Aridlandscapeandlandformdevelopment3.1.2.3
ANSWERS
Q4
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Comparingtwodistinctivedesertlandscapes,howmighteachofthevariables
affectthedevelopmentofthenamedfeatures
Thedevelopment Hotterthanusualtemperature:
ofchotts
• Fasterthanusualevaporation,causingtherapidformationofsaltsanda
thickcrustonthelakesurface.
• Ephemeralwaterisavailableforshorterperiodsoftime.
Unusuallywetyear:
• Saltlakesexpandinsize,asthereisnooutlettothesea.
• Vegetationhasmorewateravailableandsogrowsmorethanusual.
• Therearemoresaltstobedeposited,asthereismorewateravailable.
Theformationof Frequentrainfall:
alluvialfans
• Frequentrainfallwilltransportmoresedimentanddeposititonthe
alluvialfanmakingthefanlarger.
• Largerstreamswillcarrylargermaterial.
Largeamountofstreamsediment:
• Moresedimentwillbedepositedatthetopofthealluvialfan,asthere
maynotbeenoughenergytocontinuetocarrythesediment.
• Greaterchancethatindividualalluvialfanswillcoalesceintoabahada
(bajada)
Q5 Explainallthewaysapreviouslywetterclimatemaystillbeinfluencingkeyfeaturesina
contemporarydesertlandscape
Apreviouslywetterclimatemaystillbeinfluencingkeyfeaturesinacontemporarydesert
landscapeincluding:
• Deeperravinesandwadisthancurrentwaterflowscanaccountfor,throughwatererosion
cuttingdownwards
• Widerravines,formedontheedgeoftheplateau
• Relictfeaturessuchasinselberg,mesaandbutteformationsthatwereleftremainingafter
rapidsurfaceloweringunderwetterconditions.
• Biggeralluvialfansasmoresedimentwastransportedbymorepowerfulrivers
• Steeperpediments,astherewasmoresedimentavailabletoerodethesurfacebyabrasion
• Largesaltdepositsexistasaresultofthedryingupofaninlandsea,formedunderwetter
conditions
• Moreextensivechotts/playasexistthancurrenttemporarylakevolumescanaccountfor.
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