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雅思阅读真题.docx

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TheSpectacularEruptionofMountSt.Helens ATheeruptioninMay1980ofMountSt.Helens,WashingtonState,astoundedtheworldwith itsviolence.Agiganticexplosiontoremuchofthevolcano'ssummittofragments;theenergy releasedwasequaltothatof500ofthenuclearbombsthatdestroyedHiroshimain1945. BTheeventoccurredalongtheboundaryoftwoofthemovingplatesthatmakeuptheEarth's crust.TheymeetatthejunctionoftheNorthAmericancontinentandthePacificOcean.One edgeofthecontinentalNorthAmericanplateover-ridestheoceanicJuandeFucamicro-plate, producingthevolcanicCascaderangethatincludesMountsBaker,RainierandHood,andLassen PeakaswellasMountSt.Helens. CUntilMountSt.Helensbegantostir,onlyMountBakerandLassenPeakhadshownsignsof lifeduringthe20thcentury.AccordingtogeologicalevidencefoundbytheUnitedStates GeologicalSurvey,therehadbeentwomajoreruptionsofMountSt.Helensintherecent (geologicallyspeaking)past:around1900B.C.,andaboutA.D.1500.Sincethearrivalof Europeansintheregion,ithadexperiencedasingleperiodofspasmodicactivity,between1831 and1857.Then,formorethanacentury,MountSt.Helenslaydormant. DBy1979,theGeologicalSurvey,alertedbysignsofrenewedactivity,hadbeenmonitoring thevolcanofor18months.Itwarnedthelocalpopulationagainstbeingdeceivedbythe mountain'soutwardcalm,andforecastthataneruptionwouldtakeplacebeforetheendofthe century.Theinhabitantsoftheareadidnothavetowaitthatlong.OnMarch27,1980,afew cloudsofsmokeformedabovethesummit,andslighttremorswerefelt.Onthe28th,largerand darkerclouds,.consistingofgasandashes,.emergedandclimbedashighas20,000feet.InApril aslightlullensued,butthevolcanologistsremainedpessimistic.The,inearlyMay,thenorthern flankofthemountainbulged,andthesummitroseby500feet. EStepsweretakentoevacuatethepopulation.Most-campers,hikers,timbercuttersleftthe slopesofthemountain.Eighty-four-year-oldHarryTruman,aholidaylodgeownerwhohadlived thereformorethan50years,refusedtobeevacuated,inspiteofofficialandpublic,includingan entireclassofschoolchildren,wrotetohim,begginghimtoleave.Heneverdid. FOnMay18,at8.32int