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#16- CaseStudiesofVolcanoesII

Mt. Saint Helens, Washington, 1980

VolcanoWebSites

MountSt.HelensVolcanoCams (NationalParkService)http://www.fs.fed.us/gpnf/volcanocams/msh/

VirtualfieldtriptoMountSt.Helens(Strombolionline)http://www.swisseduc.ch/stromboli/virtual-excursions/index-en.html

CascadeVolcanoAlertLevels(USGeologicalSurvey)http://volcanoes.usgs.gov/activity/status.php#cvo

PanoramicView- MountSt.Helens(Fullscreen 360)http://www.fullscreen360.com/st-helens

Osorno volcano, ChileSakurajima volcano, Japan

Ashfall EruptionCaseHistory-Mt.SaintHelensMt.St.Helens(MSH)inSWWashingtonisoneofmanyvolcanoesinCascadeMountainsinNWUS,SWCanada;subduction zonevolcano

Mt.SaintHelens- 1980EruptionMajoreruptiononMay18,1980.Before1980,itwassymmetrical

Before

After

After1980eruption,largepartofmountainexplodedaway.

Mt.SaintHelens- 1980EruptionSequence1)Pre- 5/18/80(~50days)Gas-chargedsilicicmagmafilledareabelowvolcanocausinggroundtoswell~300ft.Geologistswarnedofpossibleexplosiveeruption.

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Mt.SaintHelens- 1980EruptionSequence1)Pre5/18/80(~50days)

BulgedevelopsonnorthsideofMt.StHelens

Mt.SaintHelens- 1980EruptionSequencePre5/18/80(~50days)

BulgedevelopsonnorthsideofMt.StHelens

ClickerQuestionWhattypeofvolcanoisMountSaintHelens?A. ShieldvolcanoB. StratovolcanoC. LavaLakevolcanoD. Riftvolcano

Mt.SaintHelens- 1980EruptionSequenceMay18,1980 Twostrongearthquakes(frommagmamoving)causedlargesthistoriclandslide.Landslidereleasedpressureonmagma,causedupwardandhorizontalexplosionofvolcanicash.

Mt.SaintHelens- 1980EruptionSequenceMay18,1980 Twostrongearthquakes(frommagmamoving)causedlargesthistoriclandslide.(a)Landslide releasedpressureonmagma,causedupwardandhorizontalexplosionofvolcanicash.

Vertical and lateral blast

Mt.SaintHelens- 1980EruptionSequenceMay18,1980 (b)Enormousforceofhorizontalexplosion knockedovertreesforlargedistancesEffects of lateral blast

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Mt.SaintHelens- 1980EruptionSequenceMay18,1980 Horizontalexplosionknockedovertreesforlargedistances

Lateral blast effects - Trees blown down

Mt.SaintHelens- 1980EruptionSequenceMay18,1980 Ashblown10milesupwarddarkenedskiesfor100sofmilesand(c)causedashfall.

Vertical blast, ashfall

Mt.SaintHelens- 1980EruptionSequenceMay18,1980 Ashblown10milesupwarddarkenedskiesfor100sofmiles.

Ephrata, WA (150 miles away)

Spokane, WA (300 miles away)

Mt.SaintHelens- 1980EruptionSequenceMay18,1980 Ashblown10milesupwarddarkenedskiesfor100sofmiles(ashcarriedbyjetstreamtoeasternUS).Ashfall wasmainlynuisance.

Mt.SaintHelens- 1980EruptionSequenceMay18,1980 Ashfall wasmainlynuisance- somedisruptionofdailylife.

Mt.SaintHelens- 1980EruptionSequenceMay18,1980 Hotashmeltedsnowtoproduceenormous(d)lahar(mudflow),whichcreatedflooding.

Lahar (mudflow)

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Mt.SaintHelens- 1980EruptionSequenceMay18,1980 Hotashmeltedsnowtoproduceenormous(d)lahar(mudflow),whichcreatedflooding.

Lahar (mudflow) effects

Mt.SaintHelens- 1980EruptionSequenceMay18,1980 63peoplewerekilled,includingonegeologist(DavidJohnston).Manymoredeathswithoutwarningsfromgeologists.

David Johnston

Mt.SaintHelens- 1980EruptionTheEruptionofMt.St.Helens video(OttoSieber 13:11- 17:20)https://www.youtube.com/watch?v=fmrZXWOVuC4

ClickerQuestionWhichdidNOTcausedamageand/ordisruptionduringtheMountSaintHelens1980eruption?A. Majorlavaflowsthatburiedtowns.B. Amajorexplosiveblastthattraveledformiles.C. Lahars(volcanicmudflows).D. Ashfallsintheregion

OtherExplosivelyVolcanoesCindercone - consistsentirelyofpyroclasticdebrisofallshapesandsizes(nolavaflows).Small,symmetricalcone;usually~shortlifespan.

OtherExplosivelyVolcanoes- CinderConeParicutinvolcano inMexico,1943;builta400mhighconein9yearsthenextinguisheditself.

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VolcanoSize- Shield,Strato,CinderConeCinderconesaremuchsmallerthantypicalstratovolcanoes,whicharemuchsmallerthanshieldvolcanoesofHawaii.

OtherExplosiveVolcanoFeaturesLavadome - bulbousmassofextremelyviscouslavathataccumulatesaroundvent,whichcangetplugged;potentialforextremelyexplosiveeruption.

Lava Dome at Mt. Saint Helens, 1984

OtherExplosivelyVolcanoesCaldera - rare,butextremelyviolenteruptionthatproduceshugecrater(10'sofkmwide).

OtherExplosivelyVolcanoes

Caldera - involvelargestvolcanoexplosivity indices(VEI≥6);commonlybeginasstratovolcano,thenenormouseruptionblowsawaytoppartofvolcano.Magmachamberempties,leavinglargeundergroundcavity,groundoveritcollapses.

OtherExplosivelyVolcanoes- CalderasKrakatau (southwestPacific, 1883)createdcraterthatextended300mbelowsealevel,producedgianttsunamithatkilled>30,000people

Tambora Eruption- 1815Pre-telegraph

VEI=77kmdiametercaldera41cubickm14,000ft.mountainGONE

1816:“Yearwithoutasummer”• CropsruinedintheeasternUSA

• FamineinEuropeandIndia• Politicalinstability

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OtherExplosiveVolcanoes- CalderasMountMazama (insouthwestOregon,~6,800yearsago)createdCraterLake

OtherExplosiveVolcanoes- CalderasSantorini (Greece,1390BC)destroyedLateMinoancivilization(legendoflostcityofAtlantis?)

ClickerQuestionWhatcausesaCalderaeruption?A. Largeamountsoflowviscositymagmapoursout

ofthegroundquickly.B. Alargemagmachamberemptiesand,asitdoes,

itsroofcollapses.C. Amountainbuildsupverytallandspewsashout

ofacrateratthesummit.D. Alloftheabove.

OtherExplosivelyVolcanoes- CalderasYellowstone (northwestWY)3largecaldera-formingeruptionsoverpast2millionyears(1.9,1.3,0.6m.y.a.)600,000yearrecurrence,eruptionswere~1000timeslargerthanMountSt.Helens,

OtherExplosivelyVolcanoes- CalderasYellowstone caldera-formingeruptionswere~1000timeslargerthanMountSt.Helens

OtherExplosivelyVolcanoes- CalderasYellowstone continuestoshowsignsofactivitywithhotsprings,geysers

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OtherExplosivelyVolcanoes- CalderasYellowstone someconsiderit“supervolcano”,difficulttopredictnexteruptionprecisely,massiveonenotexpectedsoon(>10,000years?)

ClickerQuestionWhichisNOTacommonnegativeconsequenceoflargeCalderaeruptions?A. Hugeoutputofvolcanicashintotheatmosphere.B. Hugelavaflowsthatrunacrossthelandsurface.C. Coolingoftheatmosphere.D. Explosionsthatdevastatelargeareasoftheearth’s

surface(10milesormore)