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Ch. 18 Volcanoes

Ch. 18 Volcanoes. Viscosity Tepha Vent Hot Spot Caldera. Cinder-Cone Volcano Composite Volcano Pyroclastic Flow Shield Volcano Crater. Ch. 18 Vocabulary. Magma. Proves that earth is geologically active Magma formed deep within earths surface

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Ch. 18 Volcanoes

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  1. Ch. 18 Volcanoes

  2. Viscosity Tepha Vent Hot Spot Caldera Cinder-Cone Volcano Composite Volcano PyroclasticFlow Shield Volcano Crater Ch. 18 Vocabulary

  3. Magma • Proves that earth is geologically active • Magma formed deep within earths surface • Temperatures must be high enough to melt rock - 800-1200 oC • Temperatures increase with depth • Pressure increase with depth • Increase Pressure – Decrease melting point • B/C Magma is less dense than surrounding rock, Magma rises to surface

  4. Magma Composition • Viscosity • Resistance to flow • Hotter the magma, lower the viscosity • Silica content • Determines viscosity • High content – high viscosity • Water content • High amounts of water will evaporate, build pressure • More explosive • Three Types of Magma

  5. Magma Types • Basaltic • Low Viscosity (50% Silica) • Quiet Eruptions • Andesitic • Intermediate Viscosity (60% Silica) • Intermediate Eruptions • Rhyolitic • High Viscosity (70% Silica) • Great Eruptions

  6. Volcano Locations: Ring of Fire

  7. Anatomy of a Volcano • Vent • Magma reaches the surface and lava erupts out of a vent • Lava solidifies and builds up mountain around vent • Cone (1 km wide) or Caldera (50 km wide)

  8. Types of Volcanoes • Shield • Broad gently sloping sides • Layer upon layer of basaltic lava accumulation (non-explosive) • Low viscosity

  9. Types of Volcanoes • Cinder Cone • Material exploded high into the air and comes back to earth • Steep side from explosive eruptions • More viscous lava contains more gases which fuel more explosive eruptions

  10. Types of Volcanoes • Composite • Volcanic fragments and lava eruptions – most common • Contains large amounts of silica, water, and gases • Potentially dangerous to people and environment

  11. Other locations for Volcanoes • Hot Spots • Located away from plate boundaries • High temperature mantle plumes rise towards the surface • Hawaiian Islands

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