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Cascade Volcanic Arc

Cascade Volcanic Arc. Eruptive history Potential hazards Monitoring Mitigation strategies. Willie Scott U.S. Geological Survey Vancouver, Washington Earthscope Cascadia Workshop. 40 million year history of subduction tectonics, magmatism, and volcanism

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Cascade Volcanic Arc

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  1. Cascade Volcanic Arc Eruptive history Potential hazards Monitoring Mitigation strategies Willie Scott U.S. Geological Survey Vancouver, Washington Earthscope Cascadia Workshop

  2. 40 million year history of subduction tectonics, magmatism, and volcanism • Isn’t going to stop anytime soon

  3. Volcano Hazards • Proximal areas (up to 25 km or 15 miles) subject to multiple hazards; some rapid • Lahars and floods affect valleys for tens of kilometers • Tephra fall affects areas tens to hundreds of kilometers, or more, downwind • Excess sediment in watersheds makes channels unstable for years to decades

  4. Lahars • Erosion • Burial • Impact • Altered channels Montserrat Volcano Observatory

  5. Sediment impacts on river channels can last for decades US Army Corps of Engineers US Army Corps of Engineers US Army Corps of Engineers

  6. Far-traveledtephra hazards • Loads structures • Reduces visibility • Abrasive and conductive • Health risks • Large areas; long duration • Danger to aircraft

  7. Impacts of volcanicash fallsversus thickness Less than 1 mm Irritant to lungs and eyes Airports and air traffic closed Road visibility and traction affected 1-5 mm Initial crop damage Electrical shorts and equipment damage Clogged sewage systems

  8. Impacts of volcanic ash falls 5-100 mm • Burial of forage and low crops • Major urban ash removal

  9. Impacts of volcanic ash falls 100-300 mm • Some roof collapse if ash wet • Severe damage to trees • Many power lines down • >300 mm • Heavy kill of vegetation, livestock, and aquatic life • Major roof collapse • Loading and breakage of large power lines • Roads impassable

  10. Tephra Hazards to Aviation Mount Etna-2002 Internationalcooperation

  11. 13 major centers in U.S. • Long lived • Recurrently active • Episodic at several time scales

  12. Mitigating Volcanic Risk • Assess hazards (scientists) • Monitor potentially hazardous volcanoes (scientists) • Prepare appropriate land-use and emergency-response plans (public officials, interagency groups) • Prepare site-specific plans (public and private sector)

  13. p (1800 AD) (1505 AD ~1575 AD, (1480 AD) (~800 AD) (~0 AD) Reconstructing eruptive history and long-term hazard assessment • Geologic mapping • Stratigraphic studies • Origin and extent

  14. What’s at risk? Residents per square kilometer 0-1 1-10 11-100 101-1000 1001-10,000

  15. Surface deformation Volcano monitoring • Intrusion of magma causes pressurization by: • Increasing volume • Heating of ground water • Release of gas • Results in: • Earthquakes • Ground deformation • Emission of CO2 and S • gases Input of mafic magma

  16. Volcano monitoring

  17. Mount St. Helens Monitoring Sites—9/22/05

  18. Co-Located CGPS and Seismometer Xmit antennas GPS antenna Solar panels Seismic electronics, radio, batteries To seismometer GPS electronics, radio, batteries

  19. Three Sisters, Oregon Ongoing crustal uplift 1997-?Revealed by InSAR Interferometric Synthetic Aperture Radar

  20. ContinuousGPS mm 20 N 0 -20 E 20 0 -20 U 80 0 Mean rates: North 10.7 mm/yr East -3.1 mm/yr Vertical 22.6 mm/yr -80 2001 2002 2003 2004 2005

  21. Geodetic campaigns GPS Tilt-leveling

  22. Velocity modelfrom GPS2001-2002

  23. Geochemical anomaly coincident with area of uplift

  24. Airborne Gas Monitoring MSH Gas emissions in tons/day CO2 300-2000 SO2 30-250 H2S 0-5 Figure from Ken McGee

  25. FLIR image(Forward-LookingInfrared)

  26. Spiders go where it’s too dangerous for scientists

  27. Mount St. Helens seismicity, 1980-2004 Episodic magma recharge? 1980-1986 eruption Steam and ash emissions

  28. 9/23 9/24,10 am IS 9/25 9/26, 3 pm AL1 9/27 9/28 In the beginning….. Shallow/low-energy seismic swarm similar to many past ones; interpreted to be the result of prior month’s high rainfall

  29. Unrest, Eruption, Alert Levels tremor explosion AL 3 Volcano Alert (Warning) AL 2 Volcano Advisory (Watch) AL 1 Notice of Volcanic Unrest • IC Team activated • Close cooperation among GPNF, WA-EMD, USGS

  30. Growth of welt; explosions 29 Sep 2004 01 Oct 2004 06 Oct 2004 02 Oct 2004

  31. Transition to steady-state lava-dome growth • Few ≤M0 per minute • ~M1 every minute or two • Several ~M2 per day • Slowed during summer 2005

  32. Repetitive “drumbeat” earthquakes, > 1 million to date Pacific Northwest Seismograph Network

  33. Mount St. Helens, 2005 Mont Pelée, 1902≤300-m vertical spine ~400-m “recumbent spine”…. 15 March 2005 • Gouge cover • Grooves and striae

  34. Dome 5 grows; breaks up; dome 6 begins westward movement and 5 sags down and west 4 5 3 1 2 Sept 2005 13 July 2005 5 4 6 Domes 2 and 1 now buried in talus 3

  35. Early June 2006

  36. Bezymianny Volcano, Kamchatka 50 yr after MSH-1980-type eruption 30 May 2006 Mount St. Helens renewed lava-dome growth; October 2004 to ????

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