Mt. Unzen, Japan, 1991 - PowerPoint PPT Presentation

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Mt. Unzen, Japan, 1991

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  1. Mt. Unzen, Japan, 1991 • Dormant for 200 years • Woke up in 1990; erupted into 1992 • Lots of pyroclastics • Killed the Krafts and Harry Glicken, a survivor of Mt. St. Helens • Site of volcano warning system 1991 - 43 scientists and journalists were killed by a three-mile-long pyroclastic flow, a fast-moving river of hot gas and rock that can speed along at speeds up to 450 miles per hour.

  2. Introduction to Volcanic Hazards • 50‑60 erupt each year • 3‑4 in the US (mostly in Alaska) • Many potentially active in northwestern US and Alaska • Often at remote locations • Sometimes near population centers • Japan • Philippines, • Mexico • Indonesia

  3. Introduction to Volcanic Hazards

  4. Introduction to Volcanic Hazards

  5. Locations of Volcanism 1: Plate Boundaries • Mostly along plate boundaries; 80% in the "ring of fire“. • Molten rock, including small components of dissolved gases, produced where lithospheric plates interact with other earth materials is called MAGMA • Lava- magma from a volcano Typically produce composite volcanoes, whose magma is high in silica content.

  6. Locations of Volcanism 2: Hot spots Typically produce shield volcanoes, whose magma is low in silica content. Example: Hawaiian Islands

  7. Volcano Types • Shield volcanoes • Largest type • Hawaii • Iceland • Indian Ocean Islands • Gentle slopes (about 10° ) • Among the tallest mountains • Generally non‑explosive eruptions: low silica basaltic flows • Some occurrences • Pyroclastic materials (tephra) • Lava tubes • Calderas • Rift zones (normal faults)

  8. Volcano Types • Cinder cones • Much smaller (few km2) • Steeper (>30‑35°) • Mostly pyroclastic materials • Easily eroded-poorly preserved • Often initial phase

  9. Volcano Types • Composite/Stratovolcanoes • Many in NWUS (Rainier, St. Helens, Hood) • Andesitic (intermediate) • Layers of andesite/ pyroclastics • Slopes ± 30‑35° • May erupt explosively – considered to be “most destructive”, due to eruptive style

  10. Three Types of Volcanoes Q: What sets the shape of these volcanoes? A: Magma viscosity, for the most part, which is determined by silica content and termperature

  11. Mt. St.Helens – a typical composite volcano http://www.youtube.com/watch?v=gewmUaR5sQo After Before Composite Volcanoes commonly produce Andesites – a silica-rich igneous rock

  12. Volcano Types • Volcanic Domes • Siliceous, viscous magmas(rhyolite) • Mt. Lassen, CA • Mt. St. Helens

  13. Volcanic Origins • Occurrences • Mid‑oceanic ridges (basalts) • Shield volcanoes in Iceland • Shield volcanoes over hot spots (Hawaii) • Composite volcanoes (subduction zones) • Andesitic • Common around Pacific Rim • Fissure Flows • Columbia River • Deccan Basalts, India • South Africa

  14. Volcanic Origins • Caldera eruptions • Extremely explosive and violent • Rhyolitic magmas • Volcanic domes • Craters, Calderas, and Vents • Craters • Depressions around the tops of volcanoes • Form by explosion or collapse • May be flat bottomed or funnel shaped • Much smaller than calderas Long Valley, Ca

  15. Volcanic Features • Hot Springs and Geysers Old Faithful

  16. Crater Lake, Oregon a good example of a caldera

  17. Volcanic Features • Calderas • Large diameter (20+ km) circular depressions • Explosive ejection-large scale collapse • May contain multiple vents • None in Recent times • 10 in the last 1My • 3 in North America (Yellowstone, WY. and Long Valley, CA.) • Classified as resurgent • Produce large amounts of pyroclastic debris (1,000 km3)

  18. Caldera-Forming Eruptuion @ Yellowstones ~600 ka October 7, 2003

  19. Caldera Migration

  20. Volcanic Hazards • Effects • Primary effects • Flows • Pyroclastics • Release of gases • Secondary effects • Debris flows • Mudflows • Floods • Fires

  21. Lava Flows • Pahoehoe • Fast moving (m/hr) • Low viscosity, smooth textured • Aa • Slow moving (m/day) • Blocky, sintered appearance • Control methods • Bombing (most successful in Italy) • Chilling (most successful in Iceland • Deflection walls (being tried in Iceland) • Results have been mixed

  22. Pyroclastic Hazards • Blowing of tephra into the atmosphere • Pyroclastic activity • Volcanic ash eruptions or ash falls • Rock fragments • Volcanic glass • Gases • Lateral blasts (Mt. St. Helens) • Pyroclastic flows or ash flows • Cloud of rock fragments, glass, and hot gases flowing rapidly down slope • Hot avalanche, ignimbrite, nueeardentes

  23. Volcanic Hazards

  24. A nueé ardente:Mt. St. Helens Pyroclastic Hazard

  25. Pyroclastic Hazards • Ash Fall • Cover large areas • Thousands of square kilometers • Vegetation • Surface water • Structural damage • Health hazards • Transportation problems

  26. Pyroclastic Hazards • Ash Flows • Travel at high speeds • Contain very hot materials • Examples • Martinique (Pelee, and St. Pierre) • Mt. Unzen • Montserrat (Plymouth)

  27. Volcanic Gases • Gases emitted • H2O most abundant gas emitted • CO2 next • About 90% of emitted gases • Hazardous gases seldom reach population centers • CO2 (hazardous) • Lake Nyos, Cameroon, West Africa • Killed 1,700 people and 3,000 cattle • Other gases • Most in small quantities • SO2, NOx, HF, H2S • May be injected high in the atmosphere

  28. Lake Nyos

  29. Debris Flows and Mud Flows • Debris Flows • 50%+ of the particles are 2 mm or greater • Snow and ice melted by eruption • Mt. Redoubt, Alaska flow equals the Mississippi at flood stage • Mudflows • 50% of more of particles are smaller than 2 mm • Examples • Mt. Rainier's old flows threaten large cities in Washington State (Tacoma and Seattle) • Armero, Nevada del Ruiz, Colombia (22,000 dead) • Potential large "landslides" along the north coast of the Island of Hawaii may generate large tsunamis

  30. Debris-Mudflow Hazard Map

  31. Case Histories • Mount Pinatubo, Philippines • Mount St. Helens, Washington • Pompeii‑Herculaneum, Italy

  32. Modern Vesuvius • 3 around Bay of Naples • Population density about 15,000/km2 • Herculaneum (79 A.D); 10m ash • 5,000 residents, mostly escaped

  33. Prediction of Volcanic Activity • Seismic activity • Geophysical monitoring • Topographic monitoring • Emitted gas monitoring • Geologic history • Volcanic Alert or Warning

  34. Adjustment/ Perception of Volcanic Hazard