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Volcanic Hazards

Volcanic Hazards. Lava flow. Lahar. Landslides. Ash fall. Pyroclastic flow. Volcanic Hazards. Mt. St. Helens: before the 1980 eruption. Bulge: plug that is pushed out by magma within the conduit. Pyroclastic eruption Mt. St. Helens Landslide Release of pressure Lateral blast

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Volcanic Hazards

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  1. Volcanic Hazards Lava flow Lahar Landslides Ash fall Pyroclastic flow

  2. Volcanic Hazards

  3. Mt. St. Helens: before the 1980 eruption Bulge: plug that is pushed out by magma within the conduit.

  4. Pyroclastic eruption • Mt. St. Helens • Landslide • Release of pressure • Lateral blast • Pyroclastic flow- down with the pull of gravity • Ash cloud-vertical • Ash fall

  5. Landslide • Gravitational force “pulls” unstable material down slope • Fills canyons and valleys with debris

  6. Landslide, Mt. Shasta • 300,000 years ago • 20 times more material than the Mt. St. Helens landslide

  7. Lateral Blast: extreme pyroclastic flow • In the case of Mt. St. Helens, the landslide “uncorked” the vent. • Gas and debris were released under tremendous force • Burns and destroys anything in its path

  8. Lateral Blast • Large area completely devastated (23 X19 miles) • Trees knocked down • Vegetation burned off

  9. Mt. Unzen, Japan Geologists examined volcanoes all around the world. Mt. Unzen, Japan and Mt. Hood, Washington have the potential for lateral eruptions.

  10. Pyroclastic flow: hot gas propels pyroclastic debris Gravitational force pulls hot gas and pyroclastic debris down slope from the initial vertical eruption. Montserrat, 1997

  11. Mt. Pinatubo, Philippines 1991 May reach 100 miles per hour Burns or suffocates anything in its path Pyroclastic Flow

  12. Vertical Eruptions: Plinian • If the initial eruption is vertical the force sends debris into the stratosphere

  13. Global cooling: debris blocks sunlight

  14. Mt. Pinatubo Major eruptions blocking Sun’s radiation Cooled global temperatures by .5-.6 degrees Centigrade

  15. Volcanism • 1815- Large eruption in the tropics; once thought to be Tambora in Indonesia • Global temperatures fell • Crops failed throughout Europe and famine spread • Mary Shelly told her house guests the story of Frankenstein and his creator died in the arctic because they were unable to go outside during their vacation

  16. Ash fall • Acts as an abrasive • Clogs machinery, covers vegetation, irritates lungs and eyes Photomicrograph of ash from the Mt. Tehama eruption (Lassen Peak) Ash deposited associated with the eruption of the Long Valley Caldera

  17. Iceland • Located on the North Atlantic mid-oceanic ridge • Hot spot • What type of lava? • Viscosity? • Eruptive style?

  18. Iceland's Eyjafjallajokull volcano • Volcanic eruption under ice produces steam and other gases to propel pyroclastic debris into the atmosphere • European air travel was interrupted for weeks

  19. Mt. Yasur, May 30, 2010 • Some flights rerouted or cancelled in Australia

  20. Volume of Pyroclastic Debris Ash

  21. Lahars • Remobilized ash, rock and debris by water • Water source needed: rain, snow melt

  22. Mt. St. Helens

  23. Mt. Rainier: lahars from the last 5600 years

  24. Lahars: Mt. Pinatubo

  25. Lava Flow • Destroys everything in path • People and animals can usually escape

  26. Iceland: The Eldfell volcano on the island of Heimaey • New land was created during the 1973 eruption.

  27. Jokulhlaup • One third of country is covered by active volcanoes • About 13% covered by glaciers • The lava melts the ice cap • At one point the large volume of water pours rapidly to the adjacent area

  28. Gas Emissions • Sometimes gas release is concentrated and toxic to vegetation and people Horseshoe Lake near Mammoth, California

  29. Carbon dioxide leaked out of Lake Nyos, Africa suffocating 1700 people and all animal life.

  30. Understanding Volcanic Hazards • Past history • How often • Types of hazards • Extent of hazards • Location of past events Ash deposits associated with the eruption of Santorini, Greece

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