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Chapter 5 Volcanoes and Other Igneous Activity

Chapter 5 Volcanoes and Other Igneous Activity. Magma & the Nature of Eruptions. Viscosity - resistance to flow Dictates eruptive behavior High viscosity (cooler) – thick (like stew) Low viscosity (hotter) – very fluid (like soup). High Viscosity. High silica content Andesite & Rhyolite

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Chapter 5 Volcanoes and Other Igneous Activity

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  1. Chapter 5Volcanoes and Other Igneous Activity

  2. Magma &the Nature of Eruptions • Viscosity - resistance to flow • Dictates eruptive behavior • High viscosity (cooler) – thick (like stew) • Low viscosity (hotter) – very fluid (like soup)

  3. High Viscosity • High silica content • Andesite & Rhyolite • Violent eruptions • Continental

  4. Low Viscosity • Low silica content • Basalt • Mild eruptions • Oceanic

  5. Dissolved Gases in magma/lava • 1% - 6% by weight • H2O • CO2 • SO2

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

  7. Development of Pyroclastic Flows

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

  9. Crater Lake

  10. Volcanic LandformsCrater Lake and Wizard Island

  11. Volcanic LandformsFissure Eruptions & Basalt Plateaus

  12. Volcanic LandformsFissure Eruptions & Basalt Plateaus

  13. Shield Volcanoes

  14. Cinder Volcano

  15. Composite/Strato VolcanoMount Shasta in California

  16. Composite/Strato Volcano

  17. Profiles of Volcanoes

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

  19. Mt. St. Helens after the 1980 eruption

  20. Mt. St. Helens

  21. Shiprock, New Mexico

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

  23. Volcanoes of the Cascade Range

  24. World’s Major Volcanoes

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

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

  27. Volcanoes and Climate • Mount Tambora, Indonesia – 1815 • Krakatau, Indonesia – 1883 • Mount St. Helens, Washington – 1980 • Mount Pinatubo, Phillippines - 1991

  28. Mount Vesuvius 79 A.D.

  29. End of Chapter 5

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