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Volcanoes
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AvolcanoisanopeninginEarth’scrustthatallowsmoltenrockfrombeneaththe
crusttoreachthesurface.Thismoltenrockiscalledmagmawhenitisbeneath
thesurfaceandlavawheniteruptsorflowsfromavolcano.Alongwithlava,
volcanoesalsoreleasegases,ash,androck.It’sasuperhotmixthatcanbeboth
incrediblydestructiveandcreative.
VolcanoesformattheedgesofEarth’stectonicplates.Thesehugeslabsof
Earth’scrusttravelatopthepartlymoltenmantle,thelayerbeneaththecrust.If
youcouldseetheplates,youmightthinktheylooklikepiecesofapuzzlebecause
theedgesfittogether.Butthesepuzzlepiecesmove,usuallyattheunnoticeable
paceofonlyafewincheseveryyear.Sometimes,though,platescollidewithone
anotherorpullapart,andit’sattheseactivezoneswherevolcanoesform.
Volcanoesmayalsoeruptinareascalledhotspotswherethecrustisthin.
Volcanoeseruptindifferentways,producingdifferentlandforms.Steep,coneshapedvolcanoesformwhenplatescollide.Allthepressureandheatofthe
collisionmakeforaviolenteruption.Theconeformswhenlavaandothermaterial
ejectandbuilduparoundtheopening.Thistypeofvolcanoisknownasa
stratovolcano,andMt.Rainierisagoodexample.Sometimesaneruptionisso
violentthatthetopofthevolcanocollapses,leavingahugepitorcaldera.Youcan
seecalderasinYellowstoneNationalParkandCraterLake.Whenplatespullapart,
lavaescapesthroughtherift.Thismoregentleflowcreatesnewcrustonthe
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seafloorandwide,roundedvolcanoesonthesurfacecalledshieldvolcanoes.
Hawaii’sKilaueaisashieldvolcano.Itisalsoanexampleofavolcanothatformed
overahotspot.
Volcaniceruptionscanbedeadly.EruptionsofKrakatauandTamborainIndonesia
causedthedeathsofmorethan100,000people.Dangerousastheyare,
volcanoesalsobuildandshapetheland,creatingmountainsandnewseafloorand
depositingmineralsandnutrientsthatenrichsoil.
SatelliteimagesinthegalleryarecourtesyGeoEye.
FastFacts
About90%oftheworld'svolcanoescanbefoundintheRingofFire,where
tectonicplatesmeetaroundtherimofthePacificOcean.
Worldwidethereare1,500activevolcanoesthatcoulderuptatanytime.Other
volcanoesaredormant;theyarequietfornowbutcouldbecomeactive.There
areevenextinctvolcanoes,whichareneverexpectedtoeruptagain.
VolcanoesarentuniquetoEarth.Thelargestvolcanoinoursolarsystemis
OlympusMonsonMars.ItisthreetimestallerthanMt.Everest,Earth'shighest
elevation.Mercury,Venus,andJupiter'smoonIoalsohaveorhavehadvolcanic
activity,withIobeingthemostactiveofall.
TheeruptionofMt.VesuviuswipedouttheRomancitiesofPompeiiand
Herculaneumintheyear79,killingthousandsofpeople.Manyvictimswere
coveredinash,whichhardenedtosolidrockovertime.Asthebodiesdecayed,
hollowimpressionsremainedintherock.Archaeologistspouredplasterintothe
hollowstoformdetailedcastsofthevictims,includinganimals.
Vocabulary
Term
Partof
Speech
Definition
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Term
active
volcano
Partof
Definition
Speech
volcanothathashadarecordederuptionsincethelastglacial
noun period,about10,000yearsago.
archipelagonoun
caldera
noun
composite
noun
volcano
crust
noun
extinct
volcano
geyser
agroupofcloselyscatteredislandsinalargebodyofwater.
largedepressionresultingfromthecollapseofthecenterofa
volcano.
steepvolcanomadeofhardenedlava,rock,andash.Also
knownasastratovolcano.
rockyoutermostlayerofEarthorotherplanet.
noun
volcanothatwillnolongererupt.
noun
lagoon
noun
lava
noun
magma
mantle
shield
noun
noun
naturalhotspringthatsometimeseruptswithwaterorsteam.
shallowbodyofwaterthatmayhaveanopeningtoalarger
bodyofwater,butisalsoprotectedfromitbyasandbaror
coralreef.
moltenrock,ormagma,thateruptsfromvolcanoesor
fissuresintheEarth'ssurface.
molten,orpartiallymelted,rockbeneaththeEarth'ssurface.
middlelayeroftheEarth,madeofmostlysolidrock.
noun
large,gentlyslopingvolcanomadefromfluidlava.
volcano
tectonic
plate
volcano
noun
noun
massiveslabofsolidrockmadeupofEarth'slithosphere
(crustanduppermantle).Alsocalledlithosphericplate.
anopeningintheEarth'scrust,throughwhichlava,ash,and
gaseserupt,andalsotheconebuiltbyeruptions.
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