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Tuesday: bring calculator

Tuesday: bring calculator . Mt. St. Helens: A Case Study from 1980. Photo pre-eruption. Mt. St. Helens: Volcanic Precursors. Tremors around the mountain. Mt. St. Helens: Volcanic Precursors. Harmonic tremors are different from tectonic movements. Mt. St. Helens: March 20.

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Tuesday: bring calculator

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  1. Tuesday: bring calculator

  2. Mt. St. Helens: A Case Study from 1980 Photo pre-eruption

  3. Mt. St. Helens: Volcanic Precursors Tremors around the mountain

  4. Mt. St. Helens: Volcanic Precursors Harmonic tremors are different from tectonic movements

  5. Mt. St. Helens: March 20 Quakes triggered snow avalanches

  6. Mt. St. Helens: March 21-26 Earthquake activity dramatically increases

  7. Mt. St. Helens: March 27 Dark ash blankets the top of the mountain: Phreatic eruption

  8. Mt. St. Helens: March 27 Phreatic eruption = steam related, with ash Magma+ groundwater = explosion

  9. Mt. St. Helens: March 27 Crater is formed

  10. Mt. St. Helens: March 28 12 explosions occur Ash landslides

  11. Mt. St. Helens: March 31 Harry Truman refuses to leave

  12. Mt. St. Helens: April 1 Huge crater develops: 200 feet deep and growing 4/3/80: 1500’ wide, 300’ deep

  13. Mt. St. Helens: April 7-April 11 Now a bulge develops on the side of the volcano

  14. Mt. St. Helens: April 7-April 11 And yet the crater keeps growing: 500’ deep

  15. Mt. St. Helens: April 11-26 Bulge is still there, but explosions cease on 4/26… is it over, or is the pressure building? 4/29: nearly 1 mile across

  16. The Bulge: March 29 through May 2

  17. May 7: Explosions resume, end May 15 May 17…

  18. Eruption Warnings: Volcanic Precursors • Small changes in summit elevations or slope steepness can be observed bylasers oftiltmeters

  19. Mt. St. Helens Case Study • Last eruption: 1857 • Activity begins in March • Eruption occurred in May

  20. Mt. St. Helens

  21. 5/18/80

  22. Harmonic tremors Ground swelling or tilting Emitting steam and gases Increased ground temperatures Small phreatic eruptions (water) Volcanic Precursors

  23. Ground swelling

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