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Volcanic Hazards in the U.S. Outline • Cascades – – – – – Mt. St. Helens Mt. Rainier Crater Lake Mt. Shasta Lassen • Other eruptions – Yellowstone – Long Valley – Valles Caldera Locations of U.S. Volcanoes Subduction Zone Volcanoes Cascades • Subduction of Juan de Fuca plate beneath North America • Water released from slab aids melting above • Magma travels toward surface, some cools, other erupts • 6-7 of these volcanoes have erupted in last 200 years Cascades Mt. St. Helens • Very active over last 4000 years • Eruptions ~ every century – Date past eruptions using old deposits St. Helens (pre-1980) Mt. St. Helens 1980 • March: small magnitude earthquakes – Indicates magma moving – Also northern side bulge Mt. St. Helens 1980 mi2 • April: 1.2 bulge rising 100 m – Growing by 1.5 m/day bulge Mt. St. Helens 1980 • May 18th: – Magnitude 5.1 earthquake – Triggered landside on north side QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Mt. St. Helens 1980 • May 18th: – Lahars forming after landslide • Snow, ice near top of mountain Bridge destroyed by lahar QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Mt. St. Helens 1980 • May 18th: – Lateral blast - pyroclastic flow • Occurred after landslide removed pressure on side of mountain • Destroyed area ~550 km2 • Timescale: minutes from earthquake QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Mt. St. Helens 1980 • May 18th: – Vertical eruption • Plinian eruption, reached 12 mi (20 km) high • 1 km2 ash Mt. St. Helens, post eruption • Rebuilding – Different shape – Lava dome builds QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Effects of 1980 eruption • • • • 62 deaths Significant stream/valley modification Clogged Columbia River, shipping channels Forest destruction Mt. St. Helens Figs Ash removed in Idaho Current Activity, Mt. St. Helens • Sept. 23, 2004 - volcano started grumbling again – Earthquakes, uplifted crater floor, some steam eruptions 9 days later QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Current Activity, Mt. St. Helens • Growth of new lava dome QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Current Activity, Mt. St. Helens New dome growth indicates magma moving to surface, producing steam QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Oct 2004 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Steam plume, Jan3 2005 Cascades Mt. Rainier • Classified as most dangerous volcano in U.S. – – – – Large glacier system Frequent earthquakes Active springs Just outside SeattleTacoma QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Why So Dangerous? • Could have eruption/landslide like St. Helens – Springs act to weaken structure • Significant lahar potential Previous Activity • Mudflows date back 5,000+ years • Most recent 500 years ago • Significant population centers on lowlands (~100,000 people) Activity Cascades Crater Lake • Today popular tourist spot Mt. Mazama 5677 B.C. • Stratovolcano in Cascades • Major eruption of lava, pyroclastic debris – Covered much of Pacific Northwest, Canada with thick layer Crater Formation • Magma chamber empties, leaves void • Top collapses Crater Formation • Magma chamber empties, leaves void • Top collapses Lake Formation • Forms over time • Small volcanic cone in center Cascades Mt. Shasta and Shastina • 2nd and 3rd largest volcanoes in Cascades – Last eruption in 1786, at least 3x in last 750 years – Development ongoing in region Mt. Shasta Lahar paths Pyroclastic Flow Danger Note the increasing number of towns/developments in higher hazard zones Cascades Lassen Peak • Actually lava dome forming in region of past large volcano • Significant eruptions in 1914-1917 – Lava flows, pyroclastic flows, ash cloud – Eruptions may have been helped by melting snow adding to groundwater system Lassen Outside Cascades • Significant caldera events in – Yellowstone – Long Valley – Valles Yellowstone, WY • Hotspot volcanism, makes tracks across U.S. • Youngest volcanics at Yellowstone – Eruptions at 2 million, 1.3 million, 600,000 years ago – Catastrophic eruptions! (600,000 yr event - VEI 8) – Active system, geysers, geothermal activity today QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Yellowstone event 600,000 years ago • Erupted ~1,000 km3 of magma – Mt. St. Helens 1km3 of magma • Created caldera 75 km long, 45 km wide Long Valley Caldera • Not traditional hotspot, but active magma system • Large eruption ~760,000 years ago – Covered 1,500 km3 with pyroclastic flow • “Activity” in 1980, more next time Long Valley QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Valles Caldera • Associated with Rio Grande Rift • Last eruption ~1 million years ago QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Next Time • Volcanic eruption prediction efforts