很多雅思考生在閱讀了雅思真題后，或許更了解了出題思路和解題方法，但不知大家有沒有做過有心人，發掘雅思閱讀真題的其它功能呢？其實，通過雅思閱讀真題也可以有的放矢地擴充雅思詞匯量。今天，環球雅思向大家推薦一篇地理類科普性的雅思閱讀真題文章SandDuner。閱讀本文后，大家在豐富知識面之余，雅思詞匯量也在不知覺中上漲哦。

雅思閱讀真題SandDune

Theaccumulationofwindblownsandmarksthebeginningofoneofnature'smostinterestingandbeautifulphenomena.Sanddunesoccurthroughouttheworld,fromcoastalandlakeshoreplainstoariddesertregions.Inadditiontotheremarkablestructureandpatternsofsanddunes,theyalsoprovidehabitatsforavarietyoflifewhichismarvelouslyadaptedtothisuniqueenvironment.Picturesquedunesagainstaskyofblueorafullmoon,withperfectlycontouredshadowsofripplesandundulatingcrests,havealwaysbeenafavoritesubjectofphotographers.Duneshavealsobeenthesubjectofmanydesertmovies,andhavehistoricallybeenaformidablebarriertovehicularandrailtravel.Dependinguponone'sparticularsituation,theycanbeoneofthemostincrediblybeautiful,thrilling,eerie,treacherousorjustplaininhospitableplacesonearth.

Theoriginofsanddunesisverycomplex,buttherearethreeessentialprerequisites:

(1)Anabundantsupplyofloosesandinaregiongenerallydevoidofvegetation(suchasanancientlakebedorriverdelta);

(2)awindenergysourcesufficienttomovethesandgrains;

(3)atopographywherebythesandparticleslosetheirmomentumandsettleout.Anynumberofobjects,suchasshrubs,rocksorfencepostscanobstructthewindforcecausingsandtopileupindriftsandultimatelylargedunes.Thereareevenreportsofanthillsformingthenucleusuponwhichsanddunesarebuilt.Thedirectionandvelocityofwinds,inadditiontothelocalsupplyofsand,resultinavarietyofduneshapesandsizes.Thewindmovesindividualgrainsalongtheinclinedwindwardsurfaceuntiltheyreachthecrestandcascadedownthesteepleewardsideor"slipface,"pilingupatthebaseandslowlyencroachingonnewterritory.SomeCaliforniaduneswithcrestsonly30feethighmayadvance50feetayear,posingaseriousthreattonearbyfarmsandroads.Ifthewinddirectionisfairlyuniformovertheyears,thedunesgraduallyshiftinthedirectionoftheprevailingwind.Vegetationmaystabilizeadune,thuspreventingitsmovementwiththeprevailingwind.AlongtheOregoncoast,entireforestsmaycoversandduneareas.Sometimesseverestormsorotherdisturbancescandestroytheforestcanopyallowingsandfromnearbydunestomoveintothedisturbedarea.Infact,Mr.Wolffiahasstoodatthecrestofashiftingdunewherethetipofasitkaspruce(Piceasitchensis)wasprotrudingfromthesand.

Thestructureandmineralcompositionofsandgrainsdependsonthegeologyofthemountainsthathavebeenerodedawaybywindandwater.Althoughmostdunesarecomposedofquartzandfeldspargrains,thebrilliantsnow-whitedunesofWhiteSands,NewMexicoarecomposedofgypsum.SpectacularblacksandbeachesofthetropicalSouthPacificislandsaremadeoffinevolcanicparticles.Gleamingwhitesandsoftropicalcoralbeachesandatollsarecomposedofaglistening,microscopicassortmentofreefanimalsandalgae,includingwave-wornfragmentsofbrightly-coloredcorals,minuteone-celledforaminiferans,fragmentsofseashells,star-shapedspongespiculesandfragmentsofjointedplatesfromacommoncalcareousgreenalga(Halimeda)thatgrowsamongsubmarineseagrassmeadowsandcoralreefs.

Evidenceofabrasiononsandblastedsurfacesoftelephonepolesandpostsrevealsthatsandgrainsseldomtravelmorethanafewfeetabovetheground.Myriadsofsandgrainsbouncingandrollingupthewindwardsurfaceofaduneoftenformaseriesofridgesandtroughscalledwindripples.Bouncingsandgrainstendtolandonthewindwardsideofeachripple,thusproducingalowridge.Withoutgettingtoocomplicated,thespacingofripplesisrelatedtotheaveragedistancegrainsjump.Thisinturn,isrelatedtothewindvelocityandsizeofthegrains.Windripplesareoftenveryspectacularandphotogenic,especiallywhenthethousandsoftinyridgescatchtheshadowsofearlymorningorlateafternoon.

Forcenturies,explorersandnaturaliststhroughouttheworldhavedescribedstrangesoundsemanatingfromsanddunes.Strangesqueakingsoundsarealsoproducedbybeachsandbysimplycompressingthesandwithyourfootorpokingitwitharod.Someoftheearliestreferencesabout"acoustical"dunesarefoundinChineseandMideasternchroniclesdatingbackmorethan1500years.MarcoPolodescribedweirdsoundsonajourneythroughtheGobiDesert,andCharlesDarwinmentioneditwhiletravelingthroughChile.Thesoundshavebeenvariouslydescribedassinging,whistling,squeaking,roaringandbooming.Someaccountscomparethesoundswithdistantkettledrums,artilleryfire,thunder,low-flyingpropelleraircraft,bassviolins,pipeorgansandhummingtelegraphwires.Lowfrequencysoundsareproducedwhencloselypackedsandgrainsslideovereachother,suchasanavalanchedowntheslipfaceofadune.Thestationarysandunderneathapparentlyactsasagiantsoundingboardoramplifiertoproducetheenormousvolumeofsound.Thesandmustbeverydryforsoundproduction,andunderamicroscopethegrainsappearmoreroundedandfinelypolishedcomparedwithordinary(silent)sand.AstronomersandgeologistshavespeculatedthatthisremarkablephenomenonmaybecommoninthewindyandnearlywaterlesssanddunesonMars.

雅思閱讀真題詞匯積累：

Dune沙丘

Arid干旱的

Picturesque風景如畫的，獨特的

Formidable強大的Eerie可怕的，奇異的

Treacherous背叛的

Inhospitable