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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