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Chapter 6 Volcanoes and Related Hazards

Chapter 6 Volcanoes and Related Hazards. Volcanic Eruptions Mild or Violent. Why do volcanoes erupt so differently Mt. St. Helens – violent Hawaiian Islands - mild. Viscosity & Eruptions. Composition Temperature Dissolved Gasses. Viscosity. Viscosity. Measure of resistance to flow

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Chapter 6 Volcanoes and Related Hazards

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  1. Chapter 6Volcanoes and Related Hazards

  2. Volcanic EruptionsMild or Violent • Why do volcanoes erupt so differently • Mt. St. Helens – violent • Hawaiian Islands - mild

  3. Viscosity & Eruptions • Composition • Temperature • Dissolved Gasses Viscosity

  4. Viscosity • Measure of resistance to flow • Hotter = low viscosity • Less hot = high viscosity

  5. Silica & Viscosity • High silica • High viscosity • Andesite & Rhyolite (Granite) • Violent • Pyroclastics • Can create global problems

  6. Silica & Viscosity • Low silica • Low viscosity • Basalt (iron & magnesium) • Mild • Can create tremendous lava flows • Generally localized problems

  7. Gases & Viscosity • High viscosity traps gases • Violence associated with gases escaping when they finally reach the surface and experience decreased pressure

  8. Dissolved Gases • 1% - 6% by weight • Water Vapor - H2O • Carbon Dioxide - CO2 • Sulfur Dioxide - SO2

  9. Other Volcanic Materials • Pyroclastics – “fire fragments” • Ash/Dust - fine & glassy • Pumice - porous • Cinders - pea-size • Blocks – hardened or cooled lava

  10. Development of Pyroclastic Flows

  11. Volcanic Features • Crater - summit depression < 1 km wide • Caldera-summit depression > 1 km wide • Vent– connects surface & magma chamber

  12. Shield Volcanoes

  13. Cinder Volcano

  14. Composite/Strato VolcanoMount Shasta in California

  15. Caldera VolcanoesYellowstone & Toba

  16. Composite/Strato Volcano

  17. Profiles of Volcanoes The shape is dictated by viscosity

  18. Mt. St. Helens Prior to the 1980 Eruption

  19. Mt. St. Helens after the 1980 eruption

  20. Mt. St. Helens

  21. Plate Tectonics & Igneous Activity • Igneous activity is not random • Most volcanoes are in/near oceans • Basaltic rocks = oceans & continents • Granitic rocks = continents

  22. Volcanoes of the Cascade Range

  23. World’s Major Volcanoes

  24. Plate Tectonics & Igneous Activity • Intraplate volcanism • Occurs within a tectonic plate • Hot Spot • Hawaii • Yellowstone Park

  25. Volcanoes & Climate • Explosive eruptions • Emit gases & fine-grained debris • Solar radiation is reflected & filtered

  26. Volcanoes and Climate • Mount Tambora, Indonesia – 1815 • Mount St. Helens, Washington – 1980

  27. End of Chapter 6

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