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Hazards Mt. St. Helens Case Study Precursors Pompeii Case Study. Outline. Volcanic Hazards and Mitigation. 1/2 billion people live within 60 miles of active volcanoes. Lava flows Pyroclastic flows Ash and Pumice Lahars: Mud flows from volcano Poisonous gases. Hazards . Lava Flows.

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  1. Hazards Mt. St. Helens Case Study Precursors Pompeii Case Study Outline

  2. Volcanic Hazards and Mitigation

  3. 1/2 billion people live within 60 miles of active volcanoes

  4. Lava flows Pyroclastic flows Ash and Pumice Lahars: Mud flows from volcano Poisonous gases Hazards

  5. Lava Flows

  6. Pyroclastic ash plume:Interferes with airplane flight (causes engine failure)

  7. Redoubt Volcano, Alaska April 1990

  8. Pyroclastic flow: When plume cools, it falls to earth, creating a high-speed, hot, gaseous cloud of death

  9. Pyroclastic flow: Will the hills protect the town?

  10. Pyroclastic Flows and Surges • Pyroclastic flows can travel over surface of water

  11. Suspended Ash

  12. 3 months after eruption

  13. Ash clogs lungs and air filters

  14. Volcanic Mudflows • Ash + water = flowing wet concrete • Triggers: • eruption of volcano covered in ice or snow • heavy rain

  15. Volcanic Mudflows • Icy to boiling temperatures (hot mudflow called lahar) • Mudflows from Mount Rainier have buried valleys where many communities now sit

  16. Poisonous Gases • Pressure keeps gas dissolved in magma • At surface, gases exsolve • More escaping gas: impending eruption • Gas in atmosphere forms aerosols  volcanic smog, “vog”

  17. Poisonous Gases • Carbon dioxide in high concentrations is colorless, odorless, denser than air (hugs ground) and deadly • 1986 Cameroon: magmatic carbon dioxide bubbled out of Lake Nyos • Killed more than 1700 people, 3000 cattle

  18. Poisonous Gases • Carbon dioxide from Long Valley Caldera in eastern California has killed huge areas of trees • Other volcanic gases include sulfur dioxide, hydrogen sulfide, chlorine compounds, fluorine

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