Volcanic HazardsVolcanic Hazards50-60 volcanoes erupt each year! 50-60 volcanoes erupt each year!

2-3 in USA 2-3 in USA

Usually in unpopulated areas, but not always: Usually in unpopulated areas, but not always: JapanJapan PhilippinesPhilippines IndonesiaIndonesia ItalyItaly NW USANW USA

Volcanic HazardsVolcanic HazardsPlate tectonics and volcanismPlate tectonics and volcanism

Hot spots can be either Hot spots can be either oceanicoceanic (Hawaii) or (Hawaii) or continentalcontinental (CRB, Yellowstone) (CRB, Yellowstone)

VolcanismVolcanismMid-ocean ridgesMid-ocean ridges

BasaltsBasalts from partial melting of the mantle from partial melting of the mantle

VolcanismVolcanismMid-ocean ridgesMid-ocean ridges

Iceland is the only major threatened area (hot spot?)Iceland is the only major threatened area (hot spot?)

Walla Walla

PacificPlate

IndianPlate

NazcaPlate

Antarctic Plate

AmericanPlate

EurasianPlate

AfricanPlate

EurasianPlate

0o

30o

30o

60o

75o

75o

60o ReykjanesRidge

Mid

-Atl a

ntic

Rid

geSouth East Indian

Central IndianOcean Ridge

Juan de Fucaand Gorda Ridges

Galapagos Spreading Center

Ocean RidgeSouth West Ind ian O

c. Rid

ge

East P

acific

Rise

VolcanismVolcanismHot SpotsHot Spots

Ocean islands:Ocean islands: Hawaii, Azores, Fiji, Canaries... Hawaii, Azores, Fiji, Canaries... ContinentalContinental hot spots: CRB, Yellowstone... hot spots: CRB, Yellowstone...

PacificPlate

IndianPlate

Antarctic Plate

AmericanPlate

EurasianPlate

AfricanPlate

EurasianPlate

0

30

30

60

75

75

60Bowie

YellowstoneBermuda

Baja

Hawaii

Easter

Marquesas

Pitcairn

Galapagos

San Felix

Juan Fernandez

Cobb

Iceland

Fernando

Ascension

AzoresMadeira

CanaryG. MeteorCape Verde Hoggar

TibestiDarfur

Cameroon

Ethiopia

Trindade St Helena

Tristan

Vema

Cape

Bouvet

Crozet

E. Africa

Comoro

Reunion

Gough

Kerguelen

SE Australia

Caroline

SamoaCocos

Society

Tubai

VolcanismVolcanismHot SpotsHot Spots

Plates move as hot spots remain ~ stationaryPlates move as hot spots remain ~ stationaryHawaii:Hawaii:

Oceanic Hot spot Oceanic Hot spot plumes plumes basaltbasalt

Low viscosityLow viscosity

Shield VolcanoShield Volcano

VolcanismVolcanismHot SpotsHot Spots

Plates move as hot spots remain ~ stationaryPlates move as hot spots remain ~ stationaryCRB - SRP - Yellowstone:CRB - SRP - Yellowstone:

Present

CRBG

SRP

WA

OR

CA NV

MT

WY

ID

UT

Yellowstone

Walla Walla

VolcanismVolcanismRidge and Hot Spot volcanism is Ridge and Hot Spot volcanism is

predominantly predominantly basalticbasaltic Basalts are Basalts are low viscositylow viscosity melts melts Gases escape easily and eruptions are Gases escape easily and eruptions are not explosivenot explosive Most common hazards are Most common hazards are flowsflows and and ashash deposits deposits

Subduction Zone VolcanismSubduction Zone Volcanism Melting of slab and/or dehydration Melting of slab and/or dehydration melting of melting of

mantle wedge above the slabmantle wedge above the slab Island Arc: Japan, Aleutians, Indonesia, Caribbean...Island Arc: Japan, Aleutians, Indonesia, Caribbean... Continental Arc: Cascades, AndesContinental Arc: Cascades, Andes

Subduction Zone VolcanismSubduction Zone Volcanism Basalt - andesite - dacite - rhyoliteBasalt - andesite - dacite - rhyolite Each is progressively more viscous and Each is progressively more viscous and explosiveexplosive Strato-volcanoes (composite volcanoes)Strato-volcanoes (composite volcanoes) Flows and Flows and pyroclasticspyroclastics Far more dangerous due to explosive natureFar more dangerous due to explosive nature

Subduction Zone VolcanismSubduction Zone Volcanism Volcanism in the NW USAVolcanism in the NW USA

Continental Subduction Zone (and some hot-spot) VolcanismContinental Subduction Zone (and some hot-spot) Volcanism

Real biggies: Real biggies: rhyoliterhyolite calderacaldera eruptions eruptions Long Valley, Yellowstone, Vallez in New MexicoLong Valley, Yellowstone, Vallez in New Mexico Melt base of silica-rich continental crustMelt base of silica-rich continental crust Subduction related or hot spot? Behind SZ properSubduction related or hot spot? Behind SZ proper No historic eruptions (thank goodness!)No historic eruptions (thank goodness!)

Lassen Peak is a rhyolitic Lassen Peak is a rhyolitic domedome Hydrothermal activity: hot springs, geysers Hydrothermal activity: hot springs, geysers

geothermal energygeothermal energy

Volcanic HazardsVolcanic Hazards

FlowsFlows Mostly basaltic Mostly basaltic

Hawaii: ~ 1 m/hrHawaii: ~ 1 m/hr CRBs fasterCRBs faster

Run through property, but easy to evacuate in Run through property, but easy to evacuate in advance, so little threat to lifeadvance, so little threat to life

Basalt flows in Basalt flows in Kalapana area, Kalapana area, HawaiiHawaii

The Columbia River Basalts and Oregon High Lava Plateau The Columbia River Basalts and Oregon High Lava Plateau are dominated by lava flows. are dominated by lava flows. During the peak of CRB activity (16-18 million years ago) some massive individual flows may have exceeded 2000 km3 or even 3000 km3, which would qualify them as the largest known terrestrial lava flows

Volcanic HazardsVolcanic Hazards

FlowsFlows Control?Control?

Spray water and chill (Heimaey & Mt. Helgafell: Spray water and chill (Heimaey & Mt. Helgafell: modest success... fortuitous?)modest success... fortuitous?)

Construct walls and diversionsConstruct walls and diversions Bombing? Block established channelwayBombing? Block established channelway Nothing will stop a large flowNothing will stop a large flow

Volcanic HazardsVolcanic Hazards

PyroclasticsPyroclastics Basalts in ridge-hot spotBasalts in ridge-hot spot

Ash of minor importanceAsh of minor importance Can be locally destructive, howeverCan be locally destructive, however

Wind-blown ash depositsWind-blown ash depositsHeimay, Iceland 1973Heimay, Iceland 1973

PyroclasticsPyroclastics

Subduction-related eruptionsSubduction-related eruptions Pyroclastics much more important and damagingPyroclastics much more important and damaging

1.1. Vertical ash columnsVertical ash columns (“Plinian” eruptions) (“Plinian” eruptions)

Vertical plinian ash Vertical plinian ash column from Mt. St. column from Mt. St. Helens, 1980Helens, 1980

Mount Pinatubo, Philippines, on June 12, 1991

Pyroclastics Pyroclastics

Subduction-related eruptionsSubduction-related eruptions Pyroclastics much more important and damagingPyroclastics much more important and damaging

1.1. Vertical ash columnsVertical ash columns (Plinian eruptions) (Plinian eruptions) Ash fall blanketAsh fall blanket Huge area, but more of a nuisance at a distanceHuge area, but more of a nuisance at a distance

Destroys vegetationDestroys vegetation Contaminate surface waterContaminate surface water Collapse roofsCollapse roofs

Can be thick and noxious close by (Pompeii) Can be thick and noxious close by (Pompeii) Also Also hothot

Pompeiian body postures suggest heatPompeiian body postures suggest heat

Pyroclastics Pyroclastics

Subduction-related eruptions

2. Pyroclastic flows Travel at several hundred km/hr and Travel at several hundred km/hr and 800 800ooC or higherC or higher

A. A. Gravitational collapse of ash column Gravitational collapse of ash column B. B. Lateral blast (Mt St Helens & others)Lateral blast (Mt St Helens & others)

C. C. Caldera overflowCaldera overflow

Any may Any may nuée ardentenuée ardente (glowing cloud) (glowing cloud) ignimbrite ignimbrite Hug ground as base surge, fluidized by gas contentHug ground as base surge, fluidized by gas content

Mt. St. Mt. St. HelensHelensAug. 7, Aug. 7, 19801980

Martinique after Nuée Ardente from Mont Pelée, 1902

Huge Rhyolitic EruptionsHuge Rhyolitic Eruptions Long ValleyLong Valley

Mono Craters

Mammoth Mtn

Long Valley caldera along the east side of the Sierra Nevada in east-central California

Many eruptions in last 3 Ma incl. massive, caldera-forming eruption 760,000 years ago

Most recent eruptions occurred just 500 to 600 years ago from vents along the Mono Crater-Inyo crater volcanic chain, Mono Lake to western part of Long Valley caldera

Long ValleyLong Valley Earthquakes began to increase in 1978 & 1Earthquakes began to increase in 1978 & 1stst swarms in 80's swarms in 80's Related to Related to magma chambermagma chamber 8 km below Long Valley 8 km below Long Valley 32 x 15 km 32 x 15 km calderacaldera from eruption only 760,000 yrs ago from eruption only 760,000 yrs ago 4 large earthquakes in May 19804 large earthquakes in May 1980 Resurvey Resurvey "resurgent dome" had risen 25 cm since 1975 "resurgent dome" had risen 25 cm since 1975 By 1982 had risen another 7 cm & caldera up 18-20 cmBy 1982 had risen another 7 cm & caldera up 18-20 cm Swarm = 1) magma motion? (most were harmonic)Swarm = 1) magma motion? (most were harmonic) 2) stress from deeper magma source pushing 2) stress from deeper magma source pushing

allall Swarms Swarms shallower by mid May, 1982 shallower by mid May, 1982

steam ventssteam vents formal notice of volcanic hazardformal notice of volcanic hazard later found not a strict progression of shallowing e'quakes later found not a strict progression of shallowing e'quakes

& latest May ones, although shallowest, were over a & latest May ones, although shallowest, were over a broad areabroad area

Huge Rhyolitic EruptionsHuge Rhyolitic Eruptions Long ValleyLong Valley

Why concern??Why concern?? 760,000 yr old eruption was 760,000 yr old eruption was HUGEHUGE Bishop ash fall was hundreds of meters thick locally & Bishop ash fall was hundreds of meters thick locally &

weldedwelded Ignimbrite = Bishop TuffIgnimbrite = Bishop Tuff

1 meter thick over 75 km radius & 1 cm at Kansas 1 meter thick over 75 km radius & 1 cm at Kansas City!!City!!

Huge Rhyolitic EruptionsHuge Rhyolitic Eruptions YellowstoneYellowstone

Huge Rhyolitic EruptionsHuge Rhyolitic Eruptions

Poisonous GasesPoisonous Gases Mostly steam, but also Mostly steam, but also

COCO22, CO, SO, CO, SO22, H, H22S S Rarely a problem since Rarely a problem since

diffusesdiffuses

Japan has gas monitors and sirens for some Japan has gas monitors and sirens for some volcanoes volcanoes

Lake Nios, Cameroon, 1986 Lake Nios, Cameroon, 1986

Sulfur dioxide from Mt. Pinatubo, 1991

Lake Nios, Cameroon, 1986Lake Nios, Cameroon, 1986 Slow release by Slow release by

dormant volcano dormant volcano bottom of lake in bottom of lake in crater crater

Suddenly overturned Suddenly overturned and released COand released CO22

which is heavy and which is heavy and hugged the ground hugged the ground suffocating ~2000suffocating ~2000

Mudflows and debris (coarser) flows: lahars (Java)Mudflows and debris (coarser) flows: lahars (Java) Ash & other Ash & other tephratephra become water saturated become water saturated

The premier threat of NW volcanoes: so much snow The premier threat of NW volcanoes: so much snow and ice to meltand ice to melt

They can be huge (Redoubt 1990 They can be huge (Redoubt 1990 flow with flow with discharge ~ Mississippi at flood)discharge ~ Mississippi at flood)

Mudflows and debris (coarser) flows: lahars (Java)Mudflows and debris (coarser) flows: lahars (Java) Osceola (5000 yrs) and Electron mudflows from Mt Osceola (5000 yrs) and Electron mudflows from Mt

RainierRainier

Hundreds of Hundreds of thousands of people thousands of people live in threatened live in threatened valley bottoms valley bottoms

Little warning Little warning (unlike floods)(unlike floods)

Predicting Volcanic ActivityPredicting Volcanic Activity

Some general patterns, but usually pattern for one Some general patterns, but usually pattern for one volcano not so good for anothervolcano not so good for another Seismic activitySeismic activity

earthquakes are earliest warningearthquakes are earliest warning harmonic tremors = magma motionharmonic tremors = magma motion may die to quiescent or may be calm before stormmay die to quiescent or may be calm before storm

Geophysical MonitoringGeophysical Monitoring shallow chamber usually fills prior to eruption shallow chamber usually fills prior to eruption surface surface swelling and tiltswelling and tilt heat: IR imagesheat: IR images magnetic fields hot springs and hydrologic activitymagnetic fields hot springs and hydrologic activity

Predicting Volcanic ActivityPredicting Volcanic Activity

Tilt Record of Kilauea, Hawaii

Predicting Volcanic ActivityPredicting Volcanic Activity GasesGases

Changes in gas geochemistry (relative amounts of steam, Changes in gas geochemistry (relative amounts of steam, COCO22, SO, SO22, etc), etc)

Worked at Mt St. Helens and Pinatubo (use at MSH Worked at Mt St. Helens and Pinatubo (use at MSH predicted 13 eruptions)predicted 13 eruptions)

Geologic HistoryGeologic History Mapping of volcanic rocks and deposits characterize Mapping of volcanic rocks and deposits characterize

common eruption typescommon eruption types Example: > 90% of Kilauea surface covered by lava in Example: > 90% of Kilauea surface covered by lava in

last 1500 yrs. last 1500 yrs. If had known, may never have built KalapanaIf had known, may never have built Kalapana

Best for long-range (of course)Best for long-range (of course)

Volcanic Hazard WarningsVolcanic Hazard WarningsHazard Zones on MontserratRestricted-Access, Mt. St.

Helens, 1980