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MEDIASPOTLIGHT
Volcanoes
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PARTNER
AvolcanoisanopeninginEarth’scrustthatallowsmoltenrockfrombeneaththecrusttoreachthesurface.This
moltenrockiscalledmagmawhenitisbeneaththesurfaceandlavawheniteruptsorflowsfromavolcano.Along
withlava,volcanoesalsoreleasegases,ash,androck.It’sasuperhotmixthatcanbebothincrediblydestructive
andcreative.
VolcanoesformattheedgesofEarth’stectonicplates.ThesehugeslabsofEarth’scrusttravelatopthepartly
moltenmantle,thelayerbeneaththecrust.Ifyoucouldseetheplates,youmightthinktheylooklikepiecesofa
puzzlebecausetheedgesfittogether.Butthesepuzzlepiecesmove,usuallyattheunnoticeablepaceofonlya
fewincheseveryyear.Sometimes,though,platescollidewithoneanotherorpullapart,andit’sattheseactive
zoneswherevolcanoesform.Volcanoesmayalsoeruptinareascalledhotspotswherethecrustisthin.
Volcanoeseruptindifferentways,producingdifferentlandforms.Steep,cone-shapedvolcanoesformwhenplates
collide.Allthepressureandheatofthecollisionmakeforaviolenteruption.Theconeformswhenlavaandother
materialejectandbuilduparoundtheopening.Thistypeofvolcanoisknownasastratovolcano,andMt.Rainier
isagoodexample.Sometimesaneruptionissoviolentthatthetopofthevolcanocollapses,leavingahugepitor
caldera.YoucanseecalderasinYellowstoneNationalParkandCraterLake.Whenplatespullapart,lavaescapes
throughtherift.Thismoregentleflowcreatesnewcrustontheseafloorandwide,roundedvolcanoesonthe
surfacecalledshieldvolcanoes.Hawaii’sKilaueaisashieldvolcano.Itisalsoanexampleofavolcanothatformed
overahotspot.
Volcaniceruptionscanbedeadly.EruptionsofKrakatauandTamborainIndonesiacausedthedeathsofmore
than100,000people.Dangerousastheyare,volcanoesalsobuildandshapetheland,creatingmountainsand
newseaflooranddepositingmineralsandnutrientsthatenrichsoil.
SatelliteimagesinthegalleryarecourtesyofGeoEye.
FASTFACTS
About90percentoftheworld'svolcanoescanbefoundintheRingofFire,wheretectonicplatesmeetaroundtherimof
thePacificOcean.
Worldwidethereare1,900activevolcanoesthatcoulderuptatanytime.Othervolcanoesaredormant;theyarequietfor
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nowbutcouldbecomeactive.Thereareevenextinctvolcanoes,whichareneverexpectedtoeruptagain.
VolcanoesarentuniquetoEarth.ThelargestvolcanoinoursolarsystemisOlympusMonsonMars.Itsthreetimes
higherthanMt.Everest,Earthshighestmountain.Mercury,Venus,andJupitersmoonIoalsohaveorhavehadvolcanic
activity,withIobeingthemostactiveofall.
TheeruptionofMt.VesuviuswipedouttheRomancitiesofPompeiiandHerculaneumintheyear79,killingmorethan
3,000peopleinpresent-dayItaly.Thevictimswerecoveredinash,whichhardenedovertime.Afterthebodiesdecayed,
hollowimpressionsremained.Archaeologistspouredplasterintothehollowstoformdetailedcastsofthevictims,
includinganimals.
VOCABULARY
Term
PartofSpeech
Definition
active
volcano
noun
volcanothathashadarecordederuptionsincethelastglacialperiod,about10,000
yearsago.
archipelago
noun
agroupofcloselyscatteredislandsinalargebodyofwater.
caldera
noun
largedepressionresultingfromthecollapseofthecenterofavolcano.
composite
volcano
noun
steepvolcanomadeofhardenedlava,rock,andash.Alsoknownasastratovolcano.
crust
noun
rockyoutermostlayerofEarthorotherplanet.
extinct
volcano
noun
volcanothatwillnolongererupt.
geyser
noun
naturalhotspringthatsometimeseruptswithwaterorsteam.
lagoon
noun
shallowbodyofwaterthatmayhaveanopeningtoalargerbodyofwater,butisalso
protectedfromitbyasandbarorcoralreef.
lava
noun
moltenrock,ormagma,thateruptsfromvolcanoesorfissuresintheEarth'ssurface.
magma
noun
molten,orpartiallymelted,rockbeneaththeEarth'ssurface.
mantle
noun
middlelayeroftheEarth,madeofmostlysolidrock.
shield
volcano
noun
large,gentlyslopingvolcanomadefromfluidlava.
tectonic
plate
noun
large,moveablesegmentoftheEarth'scrust.
volcano
noun
anopeningintheEarth'scrust,throughwhichlava,ash,andgaseserupt,andalsothe
conebuiltbyeruptions.
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