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

4. Locations of U.S. Volcanoes

5. Subduction Zone Volcanoes

6. 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

7. Cascades

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

9. St. Helens (pre-1980)

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

11. Mt. St. Helens 1980 April: 1.2 mi 2 bulge rising 100 m –Growing by 1.5 m/day bulge

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

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

14. Mt. St. Helens 1980 May 18th: –Lateral blast - pyroclastic flow Occurred after landslide removed pressure on side of mountain Destroyed area ~550 km 2 Timescale: minutes from earthquake

15. Mt. St. Helens 1980 May 18th: –Vertical eruption Plinian eruption, reached 12 mi (20 km) high 1 km 2 ash

16. Mt. St. Helens, post eruption Rebuilding –Different shape –Lava dome builds

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

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

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

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

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

23. Cascades

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

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

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

27. Activity

28. Cascades

29. Crater Lake Today popular tourist spot

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

31. Crater Formation Magma chamber empties, leaves void Top collapses

32. Crater Formation Magma chamber empties, leaves void Top collapses

33. Lake Formation Forms over time Small volcanic cone in center

34. Cascades

35. 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

36. Mt. Shasta

37. Lahar paths

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

39. Cascades

40. 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

41. Lassen

42. Outside Cascades Significant caldera events in –Yellowstone –Long Valley –Valles

43. 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

44. Yellowstone event 600,000 years ago Erupted ~1,000 km 3 of magma –Mt. St. Helens 1km 3 of magma Created caldera 75 km long, 45 km wide

45. Long Valley Caldera Not traditional hotspot, but active magma system Large eruption ~760,000 years ago –Covered 1,500 km 3 with pyroclastic flow “Activity” in 1980, more next time

46. Long Valley

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

48. Next Time Volcanic eruption prediction efforts