英语六级巅峰阅读附详解-第70期-地理环境.docx

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英语六级巅峰阅读附详解第70期:地理环境

Scatteredaroundtheglobearemorethan100smallregionsofisolatedvolcanicactivityknowntogeologistsashotspots.Unlikemostoftheworld'svolcanoes.theyarenotalwaysfoundattheboundariesofthegreatdriftingplatesthatmakeuptheearth'ssurface;onthecontrary,manyofchemliedeepintheinteriorofaplate.Mostofthehotspotsmoveonlyslowly,andinsomecasesthemovementoftheplatespastthemhaslefttrailsofdeadvolcanoes.Thebotspotsandtheirvolcanictrailsaremilestonesthatmarkthepassageoftheplates.Thattheplatesaremovingisnowbeyonddispute.AfricaandSouthAmerica.forexample.aremovingawayfromeachotherasnewmaterialisinjectedintotheseafloorbetweenthem.Thecomplementarycoastlinesandcertaingeologicalfeaturesthatseemtospantheoceanareremindersofwherethetwocontinentswereoncejoined.Therelativemotionoftheplatescarryingthesecontinentshasbeenconstructedindetail,butthemotionofoneplatewithrespecttoanothercannotreadilybetranslatedintomotionwithrespecttotheearth’sinterior.Itisnotpossibletodeterminewhetherbothcontinentsaremovinginoppositedirectionsorwhetheronecontinentisstationaryandtheotherisdriftingawayfromit.Hotspots.anchoredinthedeeperlayersoftheearth,providethemeasuringinstrumentsneededtoresolvethequestion.Fromananalysisofthehot-spotpopulationitappearsthattheAfricanplateisstationaryandthatithasnotmovedduringthepast30millionyears.Thesignificanceofhotspotsisnotconfinedlotheirroleasaframeofreference.Itnowappearsthattheyalsohaveanimportantinfluenceonthegeophysicalprocesseschatpropeltheplatesacrosstheglobe.Whenacontinentalplatecomestorestoverahotspot.thematerialrisingfromdeeperlayercreatesabroaddome.Asthedomegrows,itdevelopsdeepfissures(cracks);inatleastafewcasesthecontinentmaybreakentirelyalongsomeofthesefissures,sothatthehocspotinitiatestheformationofanewocean.Thusjustasearliertheorieshaveexplainedthemobilityofthecontinents,sohotspotsmayexplaintheirmutability(inconstancy).地球上散布着100多个互不相连的发生火山运动的小地区，地质学家称之为热点。同世界上绝大多数火山不同，它们通常并不位于构成地表的各个大漂移板块的交接地带。相反，其中很多位于