Volcanic Hazards 50 60 volcanoes erupt each year

Volcanic Hazards 50 -60 volcanoes erupt each year! F 2 -3 in USA Usually in unpopulated areas, but not always: F F F Japan Philippines Indonesia Italy NW USA

Volcanic Hazards Plate tectonics and volcanism Hot spots can be either oceanic (Hawaii) or continental (CRB, Yellowstone)

Volcanism Mid-ocean ridges F Basalts from partial melting of the mantle

Volcanism Mid-ocean ridges F Iceland is the only major threatened area (hot spot? ) 75 o Reykjanes Ridge Walla d - A t la n t ic Mi Juan de Fuca and Gorda Ridges 30 o Pacific Plate 0 o Eurasian Plate Ri dg Eurasian Plate e 60 o African Plate Galapagos Spreading Center Nazca Plate American Plate Ea st Pa ci 30 o ge fic R is e Indian Plate 60 o 75 o s S o ut h W e South East Indian Ocean Ridge Antarctic Plate t In n d ia O R c. d Indian i. Central Ocean Ridge

Volcanism Hot Spots Ocean islands: Hawaii, Azores, Fiji, Canaries. . . F Continental hot spots: CRB, Yellowstone. . . F 75 Iceland 60 Cobb Azores Yellowstone Bermuda 30 Baja Pacific Plate Hawaii Caroline 0 Samoa Cocos 30 Eurasian Plate Bowie Eurasian Plate Indian Plate Marquesas Society SE Australia Galapagos Easter Pitcairn Tubai Madeira G. Meteor Cape Verde Canary Tibesti Darfur Hoggar Fernando Cameroon American Plate Ascension Trindade St Helena San Felix Juan Fernandez African Plate Tristan Ethiopia Comoro E. Africa Vema Gough Cape Reunion Crozet Kerguelen Bouvet 60 Antarctic Plate 75

Volcanism Hot Spots F Plates move as hot spots remain ~ stationary Hawaii: Oceanic Hot spot plumes basalt Low viscosity Shield Volcano

Volcanism Hot Spots F Plates move as hot spots remain ~ stationary CRB - SRP - Yellowstone:

Volcanism Ridge and Hot Spot volcanism is predominantly basaltic Basalts are low viscosity melts F Gases escape easily and eruptions are not explosive F Most common hazards are flows and ash deposits F

Subduction Zone Volcanism Melting of slab and/or dehydration melting of mantle wedge above the slab F Island Arc: Japan, Aleutians, Indonesia, Caribbean. . . F Continental Arc: Cascades, Andes F

Subduction Zone Volcanism Basalt - andesite - dacite - rhyolite F Each is progressively more viscous and explosive F Strato-volcanoes (composite volcanoes) F Flows and pyroclastics F Far more dangerous due to explosive nature F

Subduction Zone Volcanism F Volcanism in the NW USA

Continental Subduction Zone (and some hotspot) Volcanism l l l Real biggies: rhyolite caldera eruptions F Long Valley, Yellowstone, Vallez in New Mexico F Melt base of silica-rich continental crust F Subduction related or hot spot? Behind SZ proper F No historic eruptions (thank goodness!) Lassen Peak is a rhyolitic dome Hydrothermal activity: hot springs, geysers geothermal energy

Volcanic Hazards Flows Mostly basaltic s Hawaii: ~ 1 m/hr s CRBs faster F Run through property, but easy to evacuate in advance, so little threat to life F

Basalt flows in Kalapana area, Hawaii

The Columbia River Basalts and Oregon High Lava Plateau are dominated by lava flows. During the peak of CRB activity (1618 million years ago) some massive individual flows may have exceeded 2000 km 3 or even 3000 km 3, which would qualify them as the largest known terrestrial lava flows

Volcanic Hazards Flows F Control? s Spray water and chill (Heimaey & Mt. Helgafell: modest success. . . fortuitous? ) s Construct walls and diversions s Bombing? Block established channelway s Nothing will stop a large flow

Volcanic Hazards Pyroclastics F Basalts in ridge-hot spot s Ash of minor importance s Can be locally destructive, however

Wind-blown ash deposits Heimay, Iceland 1973

Pyroclastics Subduction-related eruptions Pyroclastics much more important and damaging 1. Vertical ash columns (“Plinian” eruptions) l Vertical plinian ash column from Mt. St. Helens, 1980 Mount Pinatubo, Philippines, on June 12, 1991

Pyroclastics Subduction-related eruptions Pyroclastics much more important and damaging 1. Vertical ash columns (Plinian eruptions) F Ash fall blanket F Huge area, but more of a nuisance at a distance s Destroys vegetation s Contaminate surface water s Collapse roofs F Can be thick and noxious close by (Pompeii) F Also hot s Pompeiian body postures suggest heat l

Pyroclastics Martinique after Nuée Ardente from Mont Pelée, 1902 Subduction-related eruptions 2. Pyroclastic flows F Mt. St. Helens Aug. 7, 1980 Travel at several hundred km/hr and 800 o. C or higher A. Gravitational collapse of ash column B. Lateral blast (Mt St Helens & others) C. Caldera overflow Any may nuée ardente (glowing cloud) ignimbrite s Hug ground as base surge, fluidized by gas content

Huge Rhyolitic Eruptions l Long 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

l Long Valley F F F F F Earthquakes began to increase in 1978 & 1 st swarms in 80's Related to magma chamber 8 km below Long Valley 32 x 15 km caldera from eruption only 760, 000 yrs ago 4 large earthquakes in May 1980 Resurvey "resurgent dome" had risen 25 cm since 1975 By 1982 had risen another 7 cm & caldera up 18 -20 cm Swarm = 1) magma motion? (most were harmonic) 2) stress from deeper magma source pushing all Swarms shallower by mid May, 1982 s steam vents s formal notice of volcanic hazard s later found not a strict progression of shallowing e'quakes & latest May ones, although shallowest, were over a broad area

Huge Rhyolitic Eruptions l Long Valley F Why concern? ? s s s F 760, 000 yr old eruption was HUGE Bishop ash fall was hundreds of meters thick locally & welded Ignimbrite = Bishop Tuff 1 meter thick over 75 km radius & 1 cm at Kansas City!!

Huge Rhyolitic Eruptions l Yellowstone

Huge Rhyolitic Eruptions

Poisonous Gases Mostly steam, but also CO 2, CO, SO 2, H 2 S F Rarely a problem since diffuses F Sulfur dioxide from Mt. Pinatubo, 1991 Japan has gas monitors and sirens for some volcanoes F Lake Nios, Cameroon, 1986 F

Lake Nios, Cameroon, 1986 F F Slow release by dormant volcano bottom of lake in crater Suddenly overturned and released CO 2 which is heavy and hugged the ground suffocating ~2000

Mudflows and debris (coarser) flows: lahars (Java) l Ash & other tephra become water saturated The premier threat of NW volcanoes: so much snow and ice to melt F They can be huge (Redoubt 1990 flow with discharge ~ Mississippi at flood) F

Mudflows and debris (coarser) flows: lahars (Java) F Osceola (5000 yrs) and Electron mudflows from Mt Rainier Hundreds of thousands of people live in threatened valley bottoms Little warning (unlike floods)

Predicting Volcanic Activity Some general patterns, but usually pattern for one volcano not so good for another F Seismic activity s s s F earthquakes are earliest warning harmonic tremors = magma motion may die to quiescent or may be calm before storm Geophysical Monitoring s s shallow chamber usually fills prior to eruption surface swelling and tilt heat: IR images magnetic fields hot springs and hydrologic activity

Predicting Volcanic Activity Tilt Record of Kilauea, Hawaii

Predicting Volcanic Activity F Gases s s F Changes in gas geochemistry (relative amounts of steam, CO 2, SO 2, etc) Worked at Mt St. Helens and Pinatubo (use at MSH predicted 13 eruptions) Geologic History s s s Mapping of volcanic rocks and deposits characterize common eruption types Example: > 90% of Kilauea surface covered by lava in last 1500 yrs. i If had known, may never have built Kalapana Best for long-range (of course)

Volcanic Hazard Warnings Restricted-Access, Mt. St. Helens, 1980 Hazard Zones on Montserrat