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V. Volcanoes and Volcanism

V. Volcanoes and Volcanism. A. Mafic Volcanism and Volcanic Rocks B. Felsic Volcanism and Volcanic Rocks. Mafic Volcanism. 6. Characteristics of formations  5. Types of Rocks  4. Types of eruptions which controls  3. Type of lava which controls 

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V. Volcanoes and Volcanism

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  1. V. Volcanoes and Volcanism A. Mafic Volcanism and Volcanic Rocks B. Felsic Volcanism and Volcanic Rocks

  2. Mafic Volcanism • 6. Characteristics of formations  • 5. Types of Rocks  • 4. Types of eruptions which controls  • 3. Type of lava which controls  • 2. Source of lava which controls  • 1. Plate tectonics 

  3. 3. Types of Lava 1. 2 . Source of Lava • Partial melting of mantle • Partial melting of dry mantle • At mantle plumes or • Divergent plate boundaries • Types of lava Basaltic • Hot(>1000oC) • Non-Viscous(runny, flows easily) • “Dry”(no H2O or C02)

  4. 4. Types of Eruptions • Non-explosive • Lava flows, streams, ponds, floods • Fountains • Spatter cones • Pyroclastic eruptions

  5. 5. Types of RocksComposition and Texture • Basalt Figs. 4.9, 4.11, 4.17, 4.18 • ‘A’a • Pahoehoe • Vesicular Basalt • Pillow Basalt • Columnar Jointing • Obsidian • Volcanic Glass

  6. 6. Characteristic Formations Fissures Through Crust • Flood basalts and basalt plateaus • Shield volcanoes • Cinder cones Calderas atop of Kilauea Shield Hawaii Cinder Cone

  7. Columnar Jointing in basalt floods • As lava floods cool and solidify • The basalt contracts and • Splits into hexagonal columns Devil’s Post Pile, California

  8. Columnar Jointing • Columnar jointing may occur in volcanic stocks (large cylindrical core of volcanoes) Devils Tower, Wyoming

  9. Pillow BasaltsEvidence of submarine eruptions

  10. Volcanic Hazards • Map out rift zones • Use topography to determine flow direction

  11. Rift Zones and Lava Flows • Kilauea, Hawaii

  12. Hawaii Hazards

  13. B. Felsic Volcanism • 6. Characteristics of volcanoes  • 5. Types of Rocks  • 4. Types of eruptions  • 3. Type of lava  • 2. Source of lava  • 1. Plate tectonics 

  14. 1, 2. Plate tectonics and Sources of Lava • Partial melting at Subduction Zone • Partial melting of continental crust • Convergent plate boundaries Fig. 3.24

  15. 3. Types of Lava • Felsic • Cool (<800oC) • Viscous • Gaseous (H2O, CO2)

  16. 4. Types of Eruptions Fig. 4.1 Mt. St. Helen’s Cascade Range • Explosive • Pyroclastic Flows and surges • Lahars (saturated pyroclastics) Fig. 4.20

  17. 1mm 5. Types of RocksComposition and Texture • Andesite (and Rhyolite) • Pumice (quenched glass froth) • Porphyritic Texture (partial crystallization and extrusion) • Welded Tuffs (welded pyroclastics) • Breccias (welded, coarse, angular pyroclatics)

  18. 6. Characteristics of Volcanism • Lava Domes Composite Volcanoes • Layers of Pyroclastics (or tephra), ash and • Lava flows Pyroclastic Layers

  19. Mt. St. Helen’s Before and After 1 mile

  20. Vocanic Hazards • Volcanic Earthquakes • Directed Blast • Tephra • Volcanic Gases • Lava Flows • Pyroclastic Flows and Surges • Lahars • Debris Avalanches, Landslides, and Tsunamis

  21. Locating Volcanoes and Volcanism • Convergent Plate Boundaries Composite Volcanoes of Andesite • Mid-Ocean Ridges Pillow basalts forming new oceanic crust • Hot spots in oceans  Forming shield volcanoes • Hot spots and divergent boundaries on continents  Forming flood basalts, shield volcanoes (maybe some composite volcanoes)

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