volcano - national geographic...
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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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