1. Chapter 5 Volcanoes and Volcanic Hazards

2. The Nature of Volcanic Eruptions All eruptions involve magma/lava The behavior of magma is determined by: Temperature Composition Gases These factors control the viscosity, which controls the nature of the eruption

3. The Nature of Volcanic Eruptions Viscosity - resistance to flow Dictates eruptive behavior High viscosity (cooler) – thick (like stew) Low viscosity (hotter) – very fluid (like soup)

4. High Viscosity High silica content (Felsic) Andesite & Rhyolite (Granitic) Violent eruptions Continental

5. Low Viscosity Low silica content (mafic) Basalt Mild eruptions Oceanic

6. Dissolved Gases in magma/lava Dissolved water in magma reduces viscosity Gases expand within magma as it ascends (decreasing pressure) The violence is related to how easily the gases escape

7. The Nature of Volcanic Eruptions Quiescent Hawaiian –Type Eruptions Basaltic lavas (low viscosity) Weeks, months or years of lava flowing Explosive Eruptions Granitic (high viscosity) Expels particles of fragmented lava and gases

8. 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

9. Development of Pyroclastic Flows

10. Volcanic Features

11. Crater Lake

12. Volcanic Landforms Crater Lake and Wizard Island

13. Volcanic Landforms Fissure Eruptions & Basalt Plateaus

15. Shield Volcanoes

16. Cinder Volcano

17. Composite/Strato Volcano

18. Caldera Volcano - Yellowstone

19. Profiles of Volcanoes

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

21. Mt. St. Helens after the 1980 eruption

22. Mt. St. Helens

24. Shiprock, New Mexico

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

26. Volcanoes of the Cascade Range

27. World’s Major Volcanoes

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

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

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

33. Mount Vesuvius 79 A.D.

34. End of Chapter 5