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EncyclopedicEntry

volcano

AvolcanoisafeatureinEarth’scrustwheremoltenrockissqueezedoutontotheEarth’ssurface.Thismoltenrockiscalledmagmawhenitisbeneaththesurfaceandlavawheniterupts,orflowsout,fromavolcano.Alongwithlava,volcanoesalsoreleasegases,ash,andsolidrock.Volcanoescomeinmanydifferentshapesandsizesbutaremostcommonlycone-shapedhillsormountains.Theyarefoundthroughouttheworld,formingridgesdeepbelowtheseasurfaceandmountainsthatarethousandsofmetershigh.About1,900volcanoesonEarthareconsideredactive,meaningtheyshowsomelevelofoccasionalactivityandarelikelytoeruptagain.Manyothersaredormantvolcanoes,showingnocurrentsignsofexplodingbutlikelytobecomeactiveatsomepointinthefuture.Othersareconsideredextinct.Volcanoesareincrediblypowerfulagentsofchange.Eruptionscancreatenewlandforms,butcanalsodestroyeverythingintheirpath.About350millionpeople(oraboutoneoutofevery20peopleintheworld)livewithinthe“dangerrange”ofanactivevolcano.Volcanologistscloselymonitorvolcanoessotheycanbetterpredictimpendingeruptionsandpreparenearbypopulationsforpotentialvolcanichazardsthatcouldendangertheirsafety.PlateTectonicsMostvolcanoesformattheboundariesofEarth’stectonicplates.TheseplatesarehugeslabsoftheEarth’scrustanduppermantle,whichfittogetherlikepiecesofapuzzle.Theseplatesarenotfixed,butareconstantlymovingataveryslowrate.Theymoveonlyafewcentimetersperyear.Sometimes,theplatescollidewithoneanotherormoveapart.Volcanoesaremostcommoninthesegeologicallyactiveboundaries.

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Thetwotypesofplateboundariesthataremostlikelytoproducevolcanicactivityaredivergentplateboundariesandconvergentplateboundaries.DivergentPlateBoundariesAtadivergentboundary,tectonicplatesmoveapartfromoneanother.Theyneverreallyseparatebecausemagmacontinuouslymovesupfromthemantleintothisboundary,buildingnewplatematerialonbothsidesoftheplateboundary.TheAtlanticOceanishometoadivergentplateboundary,aplacecalledtheMid-AtlanticRidge.Here,theNorthAmericanandEurasiantectonicplatesaremovinginoppositedirections.AlongtheMid-AtlanticRidge,hotmagmaswellsupwardandbecomespartoftheNorthAmericanandEurasianplates.Theupwardmovementandeventualcoolingofthisbuoyantmagmacreateshighridgesontheoceanfloor.Theseridgesareinterconnected,formingacontinuousvolcanicmountainrangenearly60,000kilometers(37,000miles)—thelongestintheworld.AnotherdivergentplateboundaryistheEastPacificRise,whichseparatesthemassivePacificplatefromtheNazca,Cocos,andNorthAmericanplates.Ventsandfractures(alsocalledfissures)inthesemid-oceanridgesallowmagmaandgasestoescapeintotheocean.Thissubmarinevolcanicactivityaccountsforroughly75%oftheaverageannualvolumeofmagmathatreachestheEarth’scrust.Mostsubmarinevolcanoesarefoundonridgesthousandsofmetersbelowtheoceansurface.Someoceanridgesreachtheoceansurfaceandcreatelandforms.TheislandofIcelandisapartoftheMid-AtlanticRidge.ThedivergingEurasianandNorthAmericanplatescausedtheeruptionsofEyjafjallajökull(in2010)andBardarbunga(in2014).Theseeruptionswereprecededbysignificantriftingandcrackingonthegroundsurface,whicharealsoemblematicofdivergingplatemovement.Ofcourse,divergentplateboundariesalsoexistonland.TheEastAfricanRiftisanexampleofasingletectonicplatebeingrippedintwo.AlongtheHornofAfrica,theAfricanplateistearingitselfintowhatissometimescalledtheNubianplate(tothewest,includingmostofthecurrentAfricanplate)andtheSomaliplate(totheeast,includingtheHornofAfricaandthewesternIndianOcean).Alongthisdivergent

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plateboundaryarevolcanoessuchasMountNyiragongo,intheDemocraticRepublicofCongo,andMountKilimanjaro,inKenya.ConvergentPlateBoundariesAtaconvergentplateboundary,tectonicplatesmovetowardoneanotherandcollide.Oftentimes,thiscollisionforcesthedenserplateedgetosubduct,orsinkbeneaththeplateedgethatislessdense.Thesesubductionzonescancreatedeeptrenches.Asthedenserplateedgemovesdownward,thepressureandtemperaturesurroundingitincreases,whichcauseschangestotheplatethatmeltthemantleabove,andthemeltedrockrisesthroughtheplate,sometimesreachingitssurfaceaspartofavolcano.Overmillionsofyears,therisingmagmacancreateaseriesofvolcanoesknownasavolcanicarc.ThemajorityofvolcanicarcscanbefoundintheRingofFire,ahorseshoe-shapedstringofabout425volcanoesthatedgesthePacificOcean.IfyouweretodrainthewateroutofthePacificOcean,youwouldseeaseriesofdeepcanyons(trenches)runningparalleltocorrespondingvolcanicislandsandmountainranges.TheAleutianIslands,stretchingfromAlaskatoRussiaintheBeringSea,forinstance,runparalleltotheAleutianTrench,formedasthePacificplatesubductsundertheNorthAmericanplate.TheAleutianIslandshave27oftheUnitedStates’65historicallyactivevolcanoes.ThemightyAndesMountainsofSouthAmericarunparalleltothePeru-ChileTrench.ThesemountainsarecontinuallybuiltupastheNazcaplatesubductsundertheSouthAmericanplate.TheAndesMountainsincludetheworld’shighestactivevolcano,NevadosOjosdelSalado,whichrisesto6,879meters(over22,500feet)alongtheChile-Argentinaborder.HotSpotsFormanyyears,scientistshavebeentryingtoexplainwhysomevolcanoesexistthousandsofkilometersawayfromtectonicplateboundaries.Thedominanttheory,framedbyCanadiangeophysicistJ.TuzoWilsonin1963,statesthatthesevolcanoesarecreatedbyexceptionallyhotareasfixeddeepbelowEarth’smantle.Thesehotspotsareabletoindependentlymeltthetectonicplateabovethem,creatingmagmathateruptsontothetopoftheplate.

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Inhotspotsbeneaththeocean,thetectonicactivitycreatesavolcanicmound.Overmillionsofyears,volcanicmoundscangrowuntiltheyreachsealevelandcreateavolcanicisland.Thevolcanicislandmovesaspartofitstectonicplate.Thehotspotstaysput,however.Asthevolcanomovesfartherfromthehotspot,itgoesextinctandeventuallyerodesbackintotheocean.Anewandactivevolcanodevelopsoverthehotspot,creatingacontinuouscycleofvolcanism—andastringofvolcanicislandstracingthetectonicplate’smovementovertime.ForWilsonandmanyscientists,thebestexampleofhotspotvolcanismistheHawaiianIslands.Expertsthinkthisvolcanicchainofislandshasbeenformingforatleast70millionyearsoverahotspotunderneaththePacificplate.OfalltheinhabitedHawaiianIslands,Kauaiislocatedfarthestfromthepresumedhotspotandhasthemosterodedandoldestvolcanicrocks,datedat5.5millionyears.Meanwhile,onthe“BigIsland”ofHawaii—stillfueledbythehotspot—theoldestrocksarelessthan0.7millionyearsoldandvolcanicactivitycontinuestocreatenewland.Hotspotscanalsocreateterrestrialvolcanoes.TheYellowstoneSupervolcano,forinstance,sitsoverahotspotinthemiddleoftheNorthAmericanplate,withaseriesofancientcalderasstretchingacrosssouthernIdaho.TheYellowstonehotspotfuelsthegeysers,hotsprings,andothergeologicactivityatYellowstoneNationalPark,Wyoming.WhilesomedataseemtoproveWilson’shotspottheory,morerecentscientificstudiessuggestthatthesehotspotsmaybefoundatmoreshallowdepthsintheEarth’smantleandmaymigrateslowlyovergeologictimeratherthanstayfixedinthesamespot.PrincipalTypesofVolcanoesWhilevolcanoescomeinavarietyofshapesandsizes,theyallshareafewkeycharacteristics.Allvolcanoesareconnectedtoareservoirofmoltenrock,calledamagmachamber,belowthesurfaceoftheEarth.Whenpressureinsidethechamberbuildsup,thebuoyantmagmatravelsoutasurfaceventorseriesofvents,throughacentralinteriorpipeorseriesofpipes.Theseeruptions,whichvaryinsize,material,andexplosiveness,createdifferenttypesofvolcanoes.

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StratovolcanoesStratovolcanoesaresomeofthemosteasilyrecognizableandimposingvolcanoes,withsteep,conicpeaksrisinguptoseveralthousandmetersabovethelandscape.Alsoknownascompositevolcanoes,theyaremadeupoflayersoflava,volcanicash,andfragmentedrocks.Theselayersarebuiltupovertimeasthevolcanoeruptsthroughaventorgroupofventsatthesummit’scrater.MountRainierisanimpressivestratovolcanothatrises4,392meters(14,410feet)abovesealeveljustsouthofSeattle,Washington.Overthepasthalfmillionyears,MountRainierhasproducedaseriesofalternatinglavaeruptionsanddebriseruptions.TheseeruptionshavegivenMountRainiertheclassiclayeredstructureandconicshapeofacompositevolcano.Thevolcano’speakhasalsobeencarveddownbyaseriesofglaciers,givingitacraggyandruggedshape.VolcandeFuegoandAcatenangoareapairofstratovolcanoesthatstandmorethan3,700meters(12,000feet)abovesealevelnearAntigua,Guatemala.Whilethevolcanoesareconsideredtwinsbecauseoftheirsimilarshapeandsize,theyaremadeofdifferenttypesoflavaandhavedistincteruptionhistories.WhileAcatenangoeruptsinfrequentlytoday,FuegoisconsideredtobethemostactivevolcanoinCentralAmerica,eruptingmorethan60timessince1524.ShieldVolcanoesShieldvolcanoesarebuiltalmostexclusivelyoflava,whichflowsoutinalldirectionsduringaneruption.Theseflows,madeofhighlyfluidbasaltlava,spreadovergreatdistancesandcoolinthinlayers.Overtime,thelayersbuildupandcreateagentlyslopingdomethatlookslikeawarrior’sshield.Whiletheyarenotaseye-catchingastheirsteepstratovolcanocousins,shieldvolcanoesareoftenmuchlargerinvolumebecauseoftheirbroad,expansivestructure.ShieldvolcanoesmakeuptheentiretyoftheHawaiianIslands.TheKilaueaandMaunaLoashieldvolcanoes,locatedonthe“BigIsland”ofHawaii,risefromtheoceanfloormorethan4,500meters(15,000feet)belowsealevel.ThesummitofMaunaLoastandsat4,168meters(13,677feet)abovesealevelandmorethan8,500meters(28,000feet)abovetheoceanfloor,makingittheworld’slargestactivevolcano—and,bysomeaccounts,theworld’stallestmountain.Thesmallervolcano,Kilauea,hasbeeneruptingcontinuouslysince1983,makingitoneofthe

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world’smostactivevolcanoes.TheGalapagosIslandsarealsomadeupofaseriesofshieldvolcanoes.IsabelaandFernandinaislandshaveflattertopsthanothershieldvolcanoesbecauselavaeruptsfromfissuresaroundtheirtopsandalongridgesattheirbases.Asaresult,thevolcanoesriseatthetopandgrowoutwardatthebottom—butnotinthemiddle,makingthemlooklikean“invertedsoupbowl.”PyroclasticConesPyroclasticconesarethemostprolifictypeofvolcanoonEarth.Theycandevelopaspartofstratovolcanoes,shieldvolcanoes,orindependently.Alsoknownascindercones,theyformafterviolenteruptionsblowlavaintotheair.Intheatmosphere,thelavafragmentssolidifyandfallas“cinders”aroundasingularvent.Oftenformedfromasingleeruptionorshortseriesoferuptions,pyroclasticconesonlystandatheightsoftensofmeterstohundredsofmeters.Parícutin,Mexico,isauniquepyroclasticcone.Itwasthefirstvolcanotobestudiedforitsentirelifecycle.Emergingfromacornfieldin1943,Parícutin’sexplosiveeruptionscausedittoreach80%ofitsheightof424meters(1,391feet)duringitsfirstyearofactivity.Inthattime,lavaandashburiedthenearbytownofSanJuan.Overthenexteightyears,Parícutinbuilttheremainderofitscone—andthenwentquiet.GeologistslearnedagreatdealabouttheevolutionofvolcanoesinParícutin’sshort,nine-yearlife.LavaDomesLavadomesarelikeshieldvolcanoesinthattheyarebuiltentirelyoflava.Thislava,however,istoothickandstickytomovegreatdistances.Itjustpilesuparoundthevolcanovent.Lavadomesareoftenfoundonthesummitorflanksofavolcano,buttheycanalsodevelopindependently.Likepyroclasticcones,theyonlyreachafewhundredmeters,astheyareformedduringsingulareruptionsorslowlavareleases.Oneofthemosticoniclavadomesdevelopedafterthedevastating1902eruptionofMountPeléeontheislandofMartinique.Foralmostayear,alavadomegrewoutofasummitcratercreatedfromtheeruption,reachingaheightofmorethan300meters(1,000feet).KnownastheTowerofPelée,theobelisk-shapedstructurewastwicetheheightoftheWashingtonMonument.Itultimately

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collapsedintoapileofrubbleafter11monthsofgrowth.OtherImportantVolcanicFeaturesCalderasSomevolcanoesexperiencesuchlarge,explosiveeruptionsthattheyreleasemostofthematerialintheirmagmachamber.Thiscausesthelandaroundtheeruptingventorventstocollapseinwardly,creatingcirculardepressionscalledcalderas.Dependingontheirintensityandduration,volcaniceruptionscancreatecalderasasmuchas100kilometerswide.CraterLake,Oregon,isinacalderaabout10kilometers(6miles)wide.CraterLake’scalderaresultedfromaneruptionthatoccurredmorethan7,000yearsago.Thevolcano'smagmachambercollapsed,thenfilledwithwaterfromrainandsnow,creatingthelake.CraterLakeisthedeepestlakeintheUnitedStates.DeceptionIsland,locatedoffthecoastofAntarctica,experiencedaviolenteruptionroughly10,000yearsago.Thevolcanosummitcollapsed,formingacaldera7kilometers(4.4miles)wideandfloodedwithseawater.ThecalderagivesDeceptionIslanditshorseshoeshape,whichopenstotheseathroughanarrowchannel.DeceptionIsland’suniquegeologicstructuremakesitoneoftheonlyplacesintheworldwhereoceanvesselscansaildirectlyintoanactivevolcano.CratersMuchlikecalderas,cratersaredepressionsleftafteravolcanoexperiencesalargeeruption.Whilecalderasareformedbythecollapseofmaterialinsideavolcano,cratersareformedasmaterialsexplodeoutfromavolcano.Cratersareusuallymuchsmallerthancalderas,onlyextendingtoamaximumofaboutonekilometer(.62mile)indiameter.Manyvolcanoeshavemultiplecraterscausedbydifferenteruptions.TheMalySemiachikvolcano,locatedontheKamchatkaPeninsulainfareasternRussia,hassixcratersatitssummit.Theyoungestofthesecraters,Troitsky,filledinwithwaterandsnowmelt,creatingalake140meters(459feet)deep.Thelakeishighlyacidic,asvolcanicgasescontinuetobereleasedintothewaterfromtheactivevolcanobelow.

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Lavalakesarealsofoundinvolcaniccraters.ErtaAle,avolcanoinEthiopia,hasalavalakeinitssummitcrater.Lavalakesarewheremagmahasbubbleduptothesurfaceandpooledinacrater.VolcanologistscanflyoverErtaAle’ssummitcratertoseehowthelavalakeisbehavingandpredictfuturebehavior.TypesofVolcanicEruptionsVolcaniceruptionsareasdiverseasvolcanoesthemselves—whichistosay,verydiverse!Someofthewaysvolcanologistshaveclassifiedtheseeruptionsarebasedontheheightstheyreach,thetypesofmaterialstheyeject,andtheexplosivenessoftheseejections.HawaiianHawaiianeruptionsarethecalmesteruptiontype.Theyarecharacterizedbysteadylavaeruptionsknownaslavafountainsorfirefountains.Lavafountainsareabletoreachheightsofupto2kilometers(1.2miles).ThehighlyfluidlavaassociatedwithHawaiianeruptionsflowseasilyawayfromthevolcanosummit,oftencreatingfieryriversandlakesoflavawithindepressionsonthesurroundinglandscape.TheseeruptionsarenamedaftertheHawaiianIslands,wheretheymostoftenoccur.Kilauea,whichhasbeeneruptingcontinuouslysince1983,hasproducedlavaflowscoveringmorethan100squarekilometers(37squaremiles)ontheislandofHawaii.Theseflowscontinuouslydestroyhousesandcommunitiesintheirpath,whilealsoaddingnewcoastlinetotheisland.StrombolianStrombolianeruptionsarecharacterizedbyshort-livedoutburstsoflavaratherthansteadyfountaining.ThelavaisthickerandhasahighergascontentthanthatofHawaiianeruptions.Largegasbubblesrisefromthemagmachamber,pushingthepastylavaupwarduntilthebubblesexplodeatthesummitvent.Theseexplosionscanreachheightsupto10kilometers(6.2miles)althoughmostdon’tgohigherthanafewhundredmetersintotheair.StrombolianeruptionsarenamedaftertheMediterraneanislandofStromboli,Italy.ConsideredbymanytobethemostactivevolcanoonEarth,Strombolihasbeen

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eruptingalmostcontinuouslyfor2,000years.Theisland’seruptionsarealmostalwaysStrombolianinnature:Smallgasexplosionsejectblobsoflavaintotheairacoupleoftimesperhour.VulcanianVulcanianeruptionsareshort-livedbutmuchmoreexplosivethanStrombolianeruptions.Verythicklavacausesgaspressuretobuildupinthemagmachamber.Whenthispressureisfinallyreleaseditcreatescanon-likeexplosionsthatcantravelfasterthan350meterspersecond(800milesperhour).Lava,rock,andasharepropelledupto20kilometers(12.4miles)intheair,althoughmosteruptioncolumnsarebetween5and10kilometershigh.Theseplumesofmaterialhavetheabilitytodriftmoderatedistancesawayfromtheeruptionsite.The2013vulcanianeruptionofSakurajima,ontheislandofKyushu,Japan,coveredthenearbycityofKagoshimainathickcoatofash.PlinianReachingashighas50kilometers(35miles)intheatmosphere,Plinianeruptionsarethelargestofalleruptiontypes.Muchlikevulcanianeruptions,theyejectmaterialsatspeedsofhundredsofmeterspersecond.Plinianeruptions,however,aremoresustainedthanthecoughingfitsofvulcanianeruptions.Theseconsistenteruptionsresultfromthevolcano’smagmaandgrowinggasbubblesrisingatasimilarvelocity.Plinianeruptionsarethemostdestructivetypeoferuption.Theyreleaseadeadlymixtureoflava,ash,andvolcanicrockssuchasscoriaandpumice,whichcanfallkilometersawayfromtheeruptionsite.Theyarealsocharacterizedbypyroclasticflow,afluidmixtureoffragmentedmaterialsandextremelyhot,toxicgases.In79CE,aseriesofPlinianeruptionsfromMountVesuviusburiedthenearbyRomancitiesofPompeiiandHerculaneum(inwhatistodayItaly).Thecitiesandtheir13,000inhabitantswereburiedinvolcanicashandrock.Rainfallmixedwiththeashandcreatedaconcrete-likesubstancethatpreservedthecityforthousandsofyears.Surtseyan

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Surtseyaneruptionsoccurwheremagmaorlavainteractswithwater,mostoftenwhenanunderseavolcanoreachestheoceansurface.Anothertermforthissortofinteractionisaphreatomagmaticeruption.Whenheatedrapidlybylava,waterflashestosteamandexpandsviolently,creatingthemostexplosiveofalleruptiontypes.Thisaggressiveinteractionbetweenwaterandheatisabletofragmentlavaintoveryfinegrainsofashthatcanreachheightsof20kilometers(12.4miles).Tonga’sislandsofHungaTongaandHungaHa'apaiareactuallythetopsofasingle,largeunderwatervolcano.In2009,thevolcanoeruptedforseveraldays,causingsteamandashtoexplodefromthewatertoaltitudesof5kilometers(3.1miles).Whiletheeruptionskilledallsignsofwildlifeonandaroundtheislands,italsoaddedhundredsofsquaremetersoflandtoHungaHa’apai.VolcanicHazardsVolcanoesaresomeofEarth’smostpotentnaturalhazardsandagentsofchange.Theyreleaseenormousamountsofenergyandmaterial,engagingnaturalprocessesthatcanmodifylandscapesatalocal,regional,andevenglobalscale.Manyvolcanicmaterialsandprocessesposeathreattohuman,animal,andotherecologicalcommunities.VolcanicGasVolcanoesregularlyreleasevolcanicgasesthatcanbedangerousatconcentratedlevels.Carbondioxideandfluorinecancollectinsoilorvolcanicash,causingcropfailure,animaldeathanddeformity,andhumanillness.Volcaniceruptionscanalsoreleasemassiveamountsofsulfurdioxide,whichrisesintothestratosphere.There,itreflectsincomingsolarradiationwhileabsorbingoutgoinglandradiation,leadingtoacoolingoftheEarth’stemperature.Inextremecases,these“volcanicwinters”cancausecropfailuresanddrasticallyaffectweather.The1815eruptionofMountTambora,Indonesia,cooledtheaverageglobaltemperaturebyasmuchas3°Celsius(5.4°Fahrenheit),causingthe“yearwithoutasummer.”LandslidesandLahars

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Theenormousenergyofvolcaniceruptionscancauselargelandslidesthatmoveatspeedsofmorethan100kilometersperhour(60milesperhour).MountSt.Helens,Washington,isastratovolcanothathadanexplosivePlinianeruptionin1980.Theeruptionproducedthelargestlandslideinrecordedhistory,coveringa36-kilometer(14-mile)areaoflandwithashandrocks.Reachingspeedsof50to80meters(165to260feet)persecond,thelandslidehadenoughpowertosurgeoveraridge400meters(1,312feet)high.Landslidescanmixwithsurroundingrivers,ice,snow,orraintoproducewaterymixturescalledlahars.Thismixtureofwater,rock,anddebriscreatesasludgethatcanobliteratealmostanythinginitspath.The1985eruptionofNevadodelRuiz,Colombia,causedsmalllaharsofrock,ash,andmeltedsnowtoflowdownintothesurroundingrivervalleys.Thelaharsgainedmomentumandsizeastheytraveledtheriverbeds,ultimatelydestroyingmorethan5,000homesandkillingmorethan23,000people.PyroclasticFlowsExplosiveeruptionssometimesproducepyroclasticflows,amixtureofhotrockfragmentsandtoxicgasesthatmovealmostlikealiquidoutandawayfromthevolcano.Reachingspeedsgreaterthan80kilometersperhour(50milesperhour)andtemperaturesbetween200-700°Celsius(392-1292°Fahrenheit),pyroclasticflowsknockdown,shatter,bury,orburnanythingintheirpath.PyroclasticflowsareresponsibleforthehauntingfiguresfromPompeiiandHerculaneum,Italy.WhilemanyscientiststhoughtresidentsofPompeiisuffocatedtodeathfromvolcanicgasesreleasedduringMountVesuvius’eruptionin79CE,newstudiessuggestthattheyactuallydiedfromextremeheatproducedbythevolcano’spyroclasticflow.VolcanologistGiuseppeMastrolorenzoandtheItalianNationalInstituteforGeophysicsandVolcanologyrecentlydiscoveredthatthepyroclasticflowthatreachedPompeiiproducedtemperaturesofupto300°Celsius(570°Fahrenheit).Theseextremetemperaturesareabletokillpeopleinafractionofasecond,causingthemtospasmincontortedpostureslikethosefoundamongsttheplastercastsofVesuvius’victims.VolcanicAsh

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Hugeplumesofvolcanicashcanspreadoverlargeareasofthesky,turningdaylightintocompletedarknessandinhibitingairtraffic.(DuringtheeruptionofIceland’sEyjafjallajökullin2011,flightstoandfromnorthernEuropeweresuspendedformorethanaweek.)Volcanicashconductselectricitywhenwetandcancontainconcentratedlevelsoftoxicmaterials,posingthreatstohumansthatcomeinclosecontactwithitonland.The1994doubleeruptionofVulcanandTavurvurinPapuaNewGuineacoveredthenearbycityofRabaulinalayerofashupto75centimeters(about2feet)deep.Rainsturnedtheashintoacement-likesubstancethatwasheavyenoughtocollapse80%ofthebuildingsinthecity.VolcanicMonitoringandResearchVolcanichazardscanbeincrediblydangeroustohumanlife.IntheUnitedStatesalone,54volcanoesareaveryhighorhighthreattopublicsafety.Bycloselymonitoringvolcanicactivity,volcanologistscanwarnpeopleofimpendingeruptions.Whilethesewarningsarenotexactpredictions,theydoprovidecommunitieswiththevaluabletimetheyneedtoprotectthemselvesagainstvolcanichazardsandensuretheirsafety.Volcanologistspredictvolcanicactivitybytakingreal-timemeasurementsandcomparingthemagainstwhathappenedinthepast.Theyuseavarietyofinstrumentsandtechnologiestomonitortemperatures,gasemissions,waterlevels,groundmovements,andchangesinthelandscape.Thesemeasurementspaintaclearportraitofavolcano’scurrentstate,whichvolcanologiststheninterpretagainsthistoricaldata.Volcanologistsissueeruptionwarningswhenthesemeasurementsstrayfarfromthenormormirrorthosethatprecededahistoriceruption.Differentcountriesusedifferentsystemstoissueeruptionwarningstothepublic.Allofthesesystemscategorizetheiralertsbasedontheprobabilityandseverityofanimpendingeruption.Typicalvolcanicbehaviorisoftenrepresentedbythenumber1orthecolorgreen,whileanimminentandpotentiallydestructiveeruptionistypicallyrepresentedbythenumber4orthecolorred.

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Anumberofinternationalorganizationsleadthewayinvolcanicmonitoringandresearch,providinginvaluableinformationtoscientists,volcanologists,andthepublicalike.TheSmithsonianInstitution’sGlobalVolcanismProgramdocumentscurrentactivityforallthevolcanoesontheplanetthroughpubliclyavailabledata,reports,andimages.Theprogramalsokeepstheworld’sonlyarchiveofvolcanicactivityfromthelast10,000years.AspartoftheUNInternationalDecadeforNaturalDisasterReduction,theInternationalAssociationofVolcanologyandChemistryoftheEarth’sInterior(IAVCEI)createdalistof16"DecadeVolcanoes"tostudybecauseofthehighrisktheyposetopublicsafety.MountNyiragongoinDemocraticRepublicoftheCongo,forexample,isdangerouslyclosetothecityofGoma.Its2002eruptionkilled50peopleandforcedroughly450,000peopletoevacuatetheircommunities.TheSantaMaríaVolcano,whichsitsrightabovethecityofQuetzaltenango,Guatemala,hasbeencontinuouslyeruptingsince2003.TheDecadeVolcanoesprogramhasbroughttogethergeologists,volcanologists,andgovernmentofficialstocloselystudythesevolcanoesandcreaterisk-mitigationplansforpotentialeruptions.

Vocabulary

Term PartofSpeech Definition

absorb verb tosoakup.

acid nounchemicalcompoundthatreactswithabasetoformasalt.Acidscancorrodesomenaturalmaterials.AcidshavepHlevelslowerthan7.

activevolcano nounvolcanothathashadarecordederuptionsincethelastglacialperiod,about10,000yearsago.

aggressive adjectiveforcefuloroffensive.altitude noun thedistanceabovesealevel.ancient adjectiveveryold.

atmosphere nounlayersofgasessurroundingaplanetorothercelestialbody.

basalt noun typeofdarkvolcanicrock.border noun naturalorartificiallineseparatingtwopiecesofland.

boundary noun lineseparatinggeographicalareas.

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buoyant adjectivecapableoffloating.

caldera nounlargedepressionresultingfromthecollapseofthecenterofavolcano.

canyon noun deep,narrowvalleywithsteepsides.

cast nounimpressionformedwhenaliquidsubstanceispouredintoaformormold,andthenhardensintothatshape.

categorize verb toarrangebyspecifictypeorcharacteristic.channel noun waterwaybetweentworelativelycloselandmasses.

cindercone nounhillcreatedbytinybitsoflavablownoutofavolcanoandfallendownaroundthevolcanicvent.Alsocalledascoriacone.

coast nounedgeoflandalongtheseaorotherlargebodyofwater.

collapse verb tofallapartcompletely.collide verb tocrashinto.column noun strong,verticalsupportstructure,suchasapillar.concentrated adjectiveitemsgatheredcloselytogetherinoneplace.

concrete nounhardbuildingmaterialmadefrommixingcementwithrockandwater.

conduct verb totransmit,transport,orcarry.contort verb todistortorbendoutofshape.convergentplateboundary noun

areawheretwoormoretectonicplatesbumpintoeachother.Alsocalledacollisionzone.

correspond verb tomatchorbesimilarto.craggy adjectiveruggedorrocky.

crater nounbowl-shapeddepressionformedbyavolcaniceruptionorimpactofameteorite.

crop noun agriculturalproduce.crust noun rockyoutermostlayerofEarthorotherplanet.

data pluralnoun

(singular:datum)informationcollectedduringascientificstudy.

debris nounremainsofsomethingbrokenordestroyed;waste,orgarbage.

deform verb toputoutofshapeordistort.

Term PartofSpeech Definition

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dense adjectivehavingpartsormoleculesthatarepackedcloselytogether.

depression noun indentationordipinthelandscape.destroy verb toruinormakeuseless.destructive adjectiveharmful.devastating adjectiveverydestructiveordamaging.diameter noun widthofacircle.

divergentboundary noun

areawheretwoormoretectonicplatesaremovingawayfromeachother.Alsocalledanextensionalboundary.

diverse adjectivevariedorhavingmanydifferenttypes.dome noun shapethatishalfofasphere.dominant adjectivemainormostimportant.

dormantvolcano nounvolcanothathaseruptedinthepastbutisunlikelytoeruptsoon.

duration noun lengthoftime.eject verb togetridoforthrowout.

electricity nounsetofphysicalphenomenaassociatedwiththepresenceandflowofelectriccharge.

emblematic adjectivesymbolicorrepresentative.emission noun dischargeorrelease.endanger verb toputatrisk.energy noun capacitytodowork.ensure verb toguarantee.erode verb towearaway.erupt verb toexplodeorsuddenlyejectmaterial.evacuate verb toleaveorremovefromadangerousplace.exclusive adjectivelimitedtoafewcharacteristics.extinct adjectivenolongerexisting.fissure noun narrowopeningorcrack.flank verb tobeorplaceatthesideofsomething.flood noun overflowofabodyofwaterontoland.fluid noun materialthatisabletoflowandchangeshape.fraction noun portionorsection.

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fragment noun pieceorpart.

geologist nounpersonwhostudiesthephysicalformationsoftheEarth.

geophysics noun studyoftheEarth'sphysicalpropertiesandprocesses.

geyser nounnaturalhotspringthatsometimeseruptswithwaterorsteam.

glacier noun massoficethatmovesslowlyoverland.Hawaiianeruption noun

relativelygentlevolcaniceruptioncharacterizedbyconsistent,effusiveflowsoflow-viscositylava.

hazard noun dangerorrisk.

HornofAfrica nounlargepeninsulainnortheastAfrica,includingthecountriesofSomalia,Djibouti,Eritrea,andEthiopia.AlsocalledtheSomaliPeninsula.

hotspot nounintenselyhotregiondeepwithintheEarththatrisestojustunderneaththesurface.Somehotspotsproducevolcanoes.

hotspring nounsmallflowofwaterflowingnaturallyfromanundergroundwatersourceheatedbyhotormoltenrock.

iconic adjectiveeventorsymbolrepresentingabelief,nation,orcommunity.

imminent adjectivelikelytooccursoon.impending adjectiveupcomingorabouttohappen.infrequent adjectiverareornotoften.inhabit verb toliveinaspecificplace.inhibit verb tosloworprevent.instrument noun tool.intensity noun measureofmagnitude.internationalorganization noun

unitmadeupofgovernmentsorgroupsindifferentcountries,usuallyforaspecificpurpose.

interpret verb toexplainorunderstandthemeaningofsomething.inverted adjectivereversedorupside-down.lahar noun flowofmudandotherwetmaterialfromavolcano.landform noun specificnaturalfeatureontheEarth'ssurface.

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landscape noun thegeographicfeaturesofaregion.

landslide nounthefallofrocks,soil,andothermaterialsfromamountain,hill,orslope.

lava nounmoltenrock,ormagma,thateruptsfromvolcanoesorfissuresintheEarth'ssurface.

lavadome noun featureformedaslavahardensoveravolcanicvent.

lavafountain nounphenomenonwherelavaisforcefullybutnotviolentlyejectedfromavolcanothroughafissureorvent.

lavalake nounlavapooledinthecenterofavolcano'scalderaorcrater.

liquid nounstateofmatterwithnofixedshapeandmoleculesthatremainlooselyboundwitheachother.

magma nounmolten,orpartiallymelted,rockbeneaththeEarth'ssurface.

magmachamber noun undergroundreservoirthatholdsmoltenrock.mantle noun middlelayeroftheEarth,madeofmostlysolidrock.massive adjectiveverylargeorheavy.

measurement nounprocessofdetermininglength,width,mass(weight),volume,distanceorsomeotherqualityorsize.

Mid-AtlanticRidge noun

underwatermountainrangethatrunsfromIcelandtoAntarctica.

mid-oceanridge noun underwatermountainrange.migrate verb tomovefromoneplaceoractivitytoanother.

mitigation nounprocessofbecomingormakingsomethingmilderandlesssevere.

modify verb tochangeoralter.molten adjectivesolidmaterialturnedtoliquidbyheat.momentum noun speed,direction,orvelocityatwhichsomethingmoves.monitor verb toobserveandrecordbehaviorordata.mountainrange noun seriesorchainofmountainsthatareclosetogether.

naturalhazard nouneventinthephysicalenvironmentthatisdestructivetohumanactivity.

obelisk noun tall,tapering,four-sidedstonestructure.obliterate verb todestroycompletely.

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oceanvessel nounship,boat,submarine,orothervehicleabletotraveltheocean.

parallel adjectiveequaldistanceapart,andnevermeeting.phreatomagmaticeruption noun

volcaniceruptionsdrivenbythedirectinteractionofmagmaandanexternalbodyofwater.

plaster nounpaste-likematerialmadeofcrushedstone(usuallylime,gypsum,andsand),water,andfiber.

Plinianeruption nounpowerful,violentvolcanicexplosioncharacterizedbypyroclasticflowsandejectionofmaterialhighintotheatmosphere.

plume noun single,upwardflowofafluid,suchaswaterorsmoke.potent adjectiveverypowerful.potential adjectivepossible.precede verb togobefore.predict verb toknowtheoutcomeofasituationinadvance.prepare verb toassembleorgetreadyforsomething.

pressure nounforcepressedonanobjectbyanotherobjectorcondition,suchasgravity.

probability noun chanceorlikelihoodofsomethinghappening.prolific adjectiveveryproductiveorabundant.public noun peopleofacommunity.pumice noun typeofigneousrockwithmanypores.

pyroclasticcone nounhillcreatedbytinybitsoflavablownoutofavolcanoandfallendownaroundthevolcanicvent.Alsocalledacindercone.

pyroclasticflow nouncurrentofvolcanicash,lava,andgasthatflowsfromavolcano.

radiation nounenergy,emittedaswavesorparticles,radiatingoutwardfromasource.

rain noun liquidprecipitation.reservoir noun naturalorman-madelake.ridge noun long,narrowelevationofearth.

rift nounbreakintheEarth'scrustcreatedbyitspreadingorsplittingapart.

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RingofFire nounhorseshoe-shapedstringofvolcanoesandearthquakesitesaroundedgesofthePacificOcean.

river noun largestreamofflowingfreshwater.

rivervalley noundepressionintheearthcausedbyarivererodingthesurroundingsoil.

rock noun naturalsubstancecomposedofsolidmineralmatter.rubble noun roughpiecesofstone.rugged adjectivehavinganirregularorjaggedsurface.scoria noun typeofrough,crustyvolcanicrock.

sealevel nounbaselevelformeasuringelevations.Sealevelisdeterminedbymeasurementstakenovera19-yearcycle.

severity noun harshnessorintensity.shieldvolcano noun large,gentlyslopingvolcanomadefromfluidlava.significant adjectiveimportantorimpressive.

sludge nounliquidwaste,suchasthatfromthecoalminingandcleaningprocess,alsocalledslurry.

snow noun precipitationmadeoficecrystals.soil noun toplayeroftheEarth'ssurfacewhereplantscangrow.solidify verb tomakesolid.

stratosphere nounlevelofEarth'satmosphere,extendingfrom10kilometers(6miles)to50kilometers(31miles)abovethesurfaceoftheEarth.

stratovolcano nounsteepvolcanomadeofhardenedlava,rock,andash.Alsoknownasacompositevolcano.

Strombolianeruption noun mildlyviolentexplosionofavolcano.

subduct verb topulldownwardorbeneathsomething.subductionzone noun areawhereonetectonicplateslidesunderanother.submarine adjectiveunderwater.suffocate verb tobeunabletobreathe.summit noun highestpointofamountain.

supervolcano nounvolcanocapableofejectingmorethan1,000cubickilometers(240cubicmiles)ofmaterial.

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surge noun,verb

sudden,strongmovementforward.

Surtseyaneruption noun

phenomenonwhereavolcanoeruptsinanocean,sea,orlake.

suspend verb totemporarilystopanactivity.sustain verb tokeepgoing.

tectonicplate nounmassiveslabofsolidrockmadeupofEarth'slithosphere(crustanduppermantle).Alsocalledlithosphericplate.

temperature noundegreeofhotnessorcoldnessmeasuredbyathermometerwithanumericalscale.

terrestrial adjectivehavingtodowiththeEarthordryland.theory noun explanationthathasnotbeenprovenasfact.thermometer noun devicethatmeasurestemperature.toxic adjectivepoisonous.

traffic nounmovementofmanythings,oftenvehicles,inaspecificarea.

trench noun long,deepdepression,eithernaturalorman-made.valuable adjectiveworthaconsiderableamountofmoneyoresteem.

velocity nounmeasurementoftherateanddirectionofchangeinthepositionofanobject.

vent nouncrackintheEarth'scrustthatspewshotgasesandmineral-richwater.

volcanicarc noun chainofvolcanoesformedatasubductionzone.volcanicash noun fragmentsoflavalessthan2millimetersacross.

volcanicgas noungassuchaswatervapororcarbondioxidethatisreleasedintotheatmospherebyavolcano.

volcanicisland noun landformedbyavolcanorisingfromtheoceanfloor.

volcanicwinter noundropinglobaltemperaturesduetovolcanicdebrisintheatmosphereblockingthesun.

volcano nounanopeningintheEarth'scrust,throughwhichlava,ash,andgaseserupt,andalsotheconebuiltbyeruptions.

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volcanohazard nounspecificdangerposedbyanactivevolcano:gas,lahar,landslide,lavaflow,pyroclasticflow,ortephra.

volcanologist noun scientistwhostudiesvolcanoes.vulcanianeruption noun

volcaniceruptioncharacterizedbyaviolentoutburstofthickvolcanicsmokeandgas.

weather nounstateoftheatmosphere,includingtemperature,atmosphericpressure,wind,humidity,precipitation,andcloudiness.

wildlife noun organismslivinginanaturalenvironment.

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Articles&ProfilesSmithsonian:GlobalVolcanismProgram—TypesandProcessesGallery

MapsNationalGeographicMagazine:DecadeVolcanoesUSGS:VolcanoHazardsProgram—VolcanoStatusMap

VideoNOVA:DeadliestVolcanoes

WebsitesNationalGeographicEnvironment:NaturalHazards—VolcanoesGlobalVolcanismProgram:FujiPBS:SavageEarth—OutofTheInferno:VolcanoesSanDiegoStateUniversity:HowVolcanoesWorkOregonStateUniversity:VolcanoWorldUSGS:WhatAreVolcanoHazards?

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