托福听写答案讲解分享 托福阅读

下面小编跟大家一起了解托福听写答案讲解分享，希望对大家的学习有所帮助。

NARRATOR:ListentopartofthelectureinanEarthScienceclass.Theclasshasbeendiscussingvolcanoes.MALEPROFESSOR:Okay.WeknowtheEarth'ssurface,thecrust,ismadeupoftectonicplates,andthesehugeslabsofrockycrustareslowlyslidingoverorunderorpasteachother.Andwesaidthatmostoftheworld'svolcanoesoccurattheboundariesofthesetectonicplateswhereyouhavehotmoltenrocksqueezingupthroughgapsbetweentheplates.Butsomevolcanoesoccurnotattheedges,butinthemiddleofacontinentaloroceanicplate.TheHawaiianIslands,forexample,arethousandsofkilometersawayfromanyplateboundary.

Andyetyouhavevastamountsofmagma,moltenrockorlava,flowingupthroughtheearth'scrust,whichmeans,ofcourse,thatvolcanicactivitytherecan'tbeexplainedsimplybyplatetectonics.So,howdoweexplainthesevolcanicanomalies,theseexceptionstothegeneralrule?Well,backin1963,ageophysicistbythenameofWilsoncameupwithahot-spottheorytoexplainhowthisparticulartypeofvolcanicactivitycanoccur,andcangoonformaybetensorevenhundredsofmillionsofyears.Wilson'stheorywasthat:hotspotsexistbelowtectonicplates,andthey'rethecauseofthesevolcanoes.Butwhatcausesthehotspots?Hmm,well,themostpopulartheorythat'sbeenproposedistheplumehypothesis.

Accordingtothishypothesis,plumes,uh,basicallycolumnsofextremelyhotmagma,theseplumeswellupfromdeepinsidetheplanet'sinterior,maybeevenasdeepasitscore,andriseallthewayuptomeltthroughtheEarth'scrust.Imagineaburningcandle,andimaginemovingasheetofheavypaperslowlyovertheflameofthecandle.You'regonnagetaseriesofburnedspotsinthepaper.Well,that'sjustlikewhat'shappeningwiththeHawaiianIslands,butinsteadofasheetofpaper,you'vegotatectonicplate,andit'smovingoverthisplumeofintenselyhotmagma.Andratherthanaseriesofburnedspotsinthepaper,you’regettingachainofvolcanicislands...wherethehotplumemeltsthroughthecrustunderthePacificOceanatonepointafteranother—withactivevolcanoesontheyoungerislandsthat’renowjustabovetheplume,andtheotherislands…well,thefartherawayfromtheplumetheyarenow,theoldertheyareandthelongeragotheirvolcanoeswentdormantorextinct.Incidentally,

volcanicislandsmayseemsmall,buttheislandknownastheBigIslandHawaiiisoneofthetallesttopographicfeaturesontheplanet,morethanfivekilometersfromtheseafloortotheoceansurface,andalmostthatmuchagain,uptoitshighestpeak.That'snearlytenkilometersfromoceanfloortothehighestpointontheisland,whichmakesittallereventhanMountEverest.So,youcanimaginethehugeamountsofmagma,orlava,that'vefloweduptoformevenjustthisoneisland,muchlessthewholechainofislands.Now,thePlumeHypothesisprovidesaprettyelegantexplanationforavolcanicanomaly,liketheHawaiianIslands.But,whileit'shypotheticallyattractive,there'sverylittledirectevidencetosupportthetheory,