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Volcanism

Volcanism. Essential Questions: What is a volcano exactly? What are the three main types of volcanoes and in what manner do they erupt?. How and Where Volcanoes Form. 1. Water in the subducted rock is released into the asthenosphere.

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Volcanism

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  1. Volcanism • Essential Questions: • What is a volcano exactly? • What are the three main types of volcanoes and in what manner do they erupt?

  2. How and Where Volcanoes Form 1. Water in the subducted rock is released into the asthenosphere. 4. Some of the magma reaches Earth’s surface, and volcanoes form on the overriding continental plate. Oceanic lithosphere Continental lithosphere Asthenosphere 3. The magma is less dense than its surroundings, so it rises. 2. The water lowers the melting temperatures of materials in the asthenosphere, leading to magma formation. Volcanoes Volcanic activity takes place primarily at subduction boundaries,

  3. How and Where Volcanoes Form Kauai Oahu Molokai Lanai Maui Hawaii The Hawaiian Islands formed over a hot spot. Volcanoes VOCABULARY volcano Magma and volcanoes also form at hot spots. hot spot Direction of Plate Movement

  4. How Magma Rises

  5. Volcanic Settings

  6. Plate Tectonics and Magma Generation

  7. Major Volcanoes Around the World

  8. Magma and Erupted Materials Gases escape easily from basaltic magma, generating relatively quiet eruptions. Hardened basaltic lava flows on land are characterized as pahoehoe or aa; if the lava cools underwater, it is characterized as pillow lava. • Parameters of volcanism: • Viscosity • Chemistry of Magma • Gases within the magma • Water content of magma

  9. Magma and Erupted Materials Magma and Erupted Materials Viscosity: Viscosity is a measure of how thick (viscous) and sticky a liquid is. Lava Flow - A 'stream' of molten rock  

  10. Magma and Erupted Materials Basaltic Magma Rhyolitic Magma AndesiticMagma Silica Content Least (~50%) Intermediate (~60%) Most (~70%) Gas Content Least Intermediate Most Viscosity Least viscous Intermediate Most viscous Type of Eruption Rarely explosive Usually explosive Sometimes explosive Melting Temp. Highest Intermediate Lowest Location Subduction boundaries Rifts, oceanic hot spots Continental hot spots Magma and Erupted Materials

  11. Volcanic Landforms A volcano’s shape and structure depend on how it erupts and what materials are released. Shield volcanoes are formed by basaltic lava that flows long distances before hardening.

  12. Tectonic Settings and Volcanic Activity

  13. Igneous __________- classified by shape, size, and orientation Intrusions

  14. There are three types of volcanic cones: • ______ – explosive eruptions, small but steep slopes, pyroclastics. • _______ – non-explosive eruptions, fluid basaltic lava, gentle broad slopes. • _________ – alternating between lava and pyroclastics, explosive and non-explosive eruptions, steep and tall. Cinder Shield Composite

  15. Volcano Types

  16. Volcanic Landforms Shield Volcano Volcanoes VOCABULARY A volcano’s shape and structure depend on how it erupts and what materials are released. shield volcano cinder cone composite volcano Shield volcanoes are formed by basaltic lava that flows long distances before hardening. lahar caldera lava plateau

  17. Shield and Composite Volcanoes

  18. Volcanic Landforms Cinder Cone Volcanoes Cinder cones are formed when molten lava is thrown into the air from a vent and breaks into drops. These drops harden into cinders that form a steep cone around the vent.

  19. Volcanic Landforms Composite Volcano Volcanoes Composite volcanoes are formed by layers of pyroclastic materials and lava that have erupted in the past.

  20. Composite volcanoes

  21. Debris Avalanche and Eruption of Mount St. Helens, Washington

  22. Volcanic Landforms Volcanoes A caldera is a large crater-shaped basin that forms when the top of a volcano collapses.

  23. Formation of Crater Lake

  24. EFFUSIVE ERUPTIONS • Generally at hots spots, spreading centers • Mantle comes directly to surface • Hot lava; low viscosity, very mafic, flows easily, gases escape easily • Forms shields, flood basalts

  25. EXPLOSIVE ERUPTIONS • Found at subduction zones • Magma low temp (800 degrees C), high viscosity, does not flow easilty, more felsic mineralogy, gases trapped, hard to predict explosions • Forms composite volcanoes, cinder cones, calderas, aerial bombs, nuee ardente gas flows, very destructive

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