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Understanding Volcanic Hazards in the U.S.: Cascades & More

Explore U.S. volcanic sites, including Mt. St. Helens & Yellowstone, studying eruptions, hazards, and current activities in the region.

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Understanding Volcanic Hazards in the U.S.: Cascades & More

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  1. Volcanic Hazards in the U.S.

  2. Outline • Cascades • Mt. St. Helens • Mt. Rainier • Crater Lake • Mt. Shasta • Lassen • Other eruptions • Yellowstone • Long Valley • Valles Caldera

  3. Locations of U.S. Volcanoes

  4. Subduction Zone Volcanoes

  5. 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

  6. Cascades

  7. Mt. St. Helens • Very active over last 4000 years • Eruptions ~ every century • Date past eruptions using old deposits

  8. St. Helens (pre-1980)

  9. Mt. St. Helens 1980 • March: small magnitude earthquakes • Indicates magma moving • Also northern side bulge

  10. Mt. St. Helens 1980 bulge • April: 1.2 mi2 bulge rising 100 m • Growing by 1.5 m/day

  11. Mt. St. Helens 1980 • May 18th: • Magnitude 5.1 earthquake • Triggered landside on north side

  12. Mt. St. Helens 1980 • May 18th: • Lahars forming after landslide • Snow, ice near top of mountain Bridge destroyed by lahar

  13. 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

  14. Mt. St. Helens 1980 • May 18th: • Vertical eruption • Plinian eruption, reached 12 mi (20 km) high • 1 km2 ash

  15. Mt. St. Helens, post eruption • Rebuilding • Different shape • Lava dome builds

  16. Effects of 1980 eruption • 62 deaths • Significant stream/valley modification • Clogged Columbia River, shipping channels • Forest destruction

  17. Ash removed in Idaho Mt. St. Helens Figs

  18. Current Activity, Mt. St. Helens • Sept. 23, 2004 - volcano started grumbling again • Earthquakes, uplifted crater floor, some steam eruptions 9 days later

  19. Current Activity, Mt. St. Helens • Growth of new lava dome

  20. Current Activity, Mt. St. Helens New dome growth indicates magma moving to surface, producing steam Oct 2004 Steam plume, Jan3 2005

  21. Cascades

  22. Mt. Rainier • Classified as most dangerous volcano in U.S. • Large glacier system • Frequent earthquakes • Active springs • Just outside Seattle-Tacoma

  23. Why So Dangerous? • Could have eruption/landslide like St. Helens • Springs act to weaken structure • Significant lahar potential

  24. Previous Activity • Mudflows date back 5,000+ years • Most recent 500 years ago • Significant population centers on lowlands (~100,000 people)

  25. Activity

  26. Cascades

  27. Crater Lake • Today popular tourist spot

  28. Mt. Mazama 5677 B.C. • Stratovolcano in Cascades • Major eruption of lava, pyroclastic debris • Covered much of Pacific Northwest, Canada with thick layer

  29. Crater Formation • Magma chamber empties, leaves void • Top collapses

  30. Crater Formation • Magma chamber empties, leaves void • Top collapses

  31. Lake Formation • Forms over time • Small volcanic cone in center

  32. Cascades

  33. 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

  34. Mt. Shasta

  35. Lahar paths

  36. Pyroclastic Flow Danger Note the increasing number of towns/developments in higher hazard zones

  37. Cascades

  38. 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

  39. Lassen

  40. Outside Cascades • Significant caldera events in • Yellowstone • Long Valley • Valles

  41. 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

  42. 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

  43. 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

  44. Long Valley

  45. Valles Caldera • Associated with Rio Grande Rift • Last eruption ~1 million years ago

  46. Next Time • Volcanic eruption prediction efforts

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