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Volcanoes Chapter 18
Magma <ul><li>minerals, dissolved Mixture of molten rock, suspended gases BELOW Earth’s surface </li></ul><ul><ul><li>Rock...
Types of Magma <ul><li>Basaltic- like basalt; dark in color; forms when rocks in asthenosphere melt; low viscosity -> flow...
Types of Magma Con’t <ul><li>Andesitic- found on continental margins (subduction)-> made from oceanic crust that travels t...
Types of magma <ul><li>Rhyolitic- forms when molten material rises through thick continental crust and mixes with silica a...
Volcano Anatomy <ul><li>Vent- hole where lava comes out </li></ul><ul><li>Crater- cone-like depression at top of volcano <...
Types of Volcanoes <ul><li>Shield- broad, gently sloping sides and circular base; form from layers of basaltic lava flows;...
Types of Volcanoes <ul><li>Cinder Cone- Ash falls back and piles up near vent; steep sides; small in size; high water and ...
Types of Volcanoes <ul><li>Composite Cone- layers of ash alternate with lava; large amounts of silica, water and gases; mu...
Volcanic Material <ul><li>Tephra- Rock fragments thrown into air by eruption- Classified by size (ash, blocks, bombs) </li...
 
Volcanoes on the web <ul><li>http://www.avo.alaska.edu/ </li></ul><ul><li>http://vulcan.wr.usgs.gov/ </li></ul><ul><li>htt...
Intrusive Activity <ul><li>Plutons- very large collections of cooled magma </li></ul><ul><ul><li>Intrusive Igneous Rock Fo...
Intrusive Activity <ul><li>Stocks- smaller irregularly shaped pluton </li></ul><ul><li>Laccolith- magma forced up into par...
Intrusive Activity <ul><li>Sills- parallel to rock layers -> like window sill </li></ul><ul><li>Dike- pluton that cuts acr...
 
Hot Spots <ul><li>Unusually hot regions of Earth’s crust where plumes of magma rise up </li></ul><ul><ul><li>Plumes move v...
 
 
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Volcanoes Lecture

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Transcript of "Volcanoes Lecture"

  1. 1. Volcanoes Chapter 18
  2. 2. Magma <ul><li>minerals, dissolved Mixture of molten rock, suspended gases BELOW Earth’s surface </li></ul><ul><ul><li>Rocks melt in asthenosphere (really hot) </li></ul></ul><ul><ul><li>Why isn’t the whole rest of the mantle liquid too? </li></ul></ul><ul><ul><ul><li>Pressure- pressure increases with depth, increased pressure raises the melting point of rock </li></ul></ul></ul><ul><ul><ul><li>Water- tiny water droplets trapped in rock raise melting point </li></ul></ul></ul>
  3. 3. Types of Magma <ul><li>Basaltic- like basalt; dark in color; forms when rocks in asthenosphere melt; low viscosity -> flows quickly & rises to surface quickly. Small amounts of silica; Quiet eruptions; Hawaii </li></ul>
  4. 4. Types of Magma Con’t <ul><li>Andesitic- found on continental margins (subduction)-> made from oceanic crust that travels through continental crust; 60% silica; high silica -> intermediate eruptions; Mount St. Helens </li></ul>
  5. 5. Types of magma <ul><li>Rhyolitic- forms when molten material rises through thick continental crust and mixes with silica and water; high viscosity -> violent eruptions; Yellowstone </li></ul><ul><li>Viscosity- hotter temperature -> lower viscosity </li></ul><ul><ul><li>Higher silica -> Higher viscosity </li></ul></ul>
  6. 6. Volcano Anatomy <ul><li>Vent- hole where lava comes out </li></ul><ul><li>Crater- cone-like depression at top of volcano </li></ul><ul><li>Magma Chamber- place under volcano where magma is stored </li></ul><ul><li>Neck- Tube where lava travels from chamber to surface </li></ul><ul><li>Caldera- large depression where top of volcano collapsed- Crater Lake, OR </li></ul>
  7. 7. Types of Volcanoes <ul><li>Shield- broad, gently sloping sides and circular base; form from layers of basaltic lava flows; non-explosive (quiet) eruptions- Hawaii </li></ul>
  8. 8. Types of Volcanoes <ul><li>Cinder Cone- Ash falls back and piles up near vent; steep sides; small in size; high water and silica content; lots of gases -> more explosive </li></ul>
  9. 9. Types of Volcanoes <ul><li>Composite Cone- layers of ash alternate with lava; large amounts of silica, water and gases; much larger than cinder cones; violently explosive; Mount St. Helens </li></ul>
  10. 10. Volcanic Material <ul><li>Tephra- Rock fragments thrown into air by eruption- Classified by size (ash, blocks, bombs) </li></ul><ul><li>Pyroclastic Flows- Clouds of gas, ash, tephra traveling at fast speeds (90mph) and at high temps (370 degrees) </li></ul>
  11. 12. Volcanoes on the web <ul><li>http://www.avo.alaska.edu/ </li></ul><ul><li>http://vulcan.wr.usgs.gov/ </li></ul><ul><li>http://hvo.wr.usgs.gov/ </li></ul><ul><li>http://lvo.wr.usgs.gov/ </li></ul><ul><li>http:// volcanoes.usgs.gov/yvo / </li></ul>
  12. 13. Intrusive Activity <ul><li>Plutons- very large collections of cooled magma </li></ul><ul><ul><li>Intrusive Igneous Rock Formations- (“Inside lava rock”) </li></ul></ul><ul><ul><li>Cut across older rocks </li></ul></ul><ul><li>Batholiths- largest pluton, millions of years to form, common in interiors of mountain chains; in N America usually granite; up to 680 miles long </li></ul>
  13. 14. Intrusive Activity <ul><li>Stocks- smaller irregularly shaped pluton </li></ul><ul><li>Laccolith- magma forced up into parallel rock layers close to surface -> push some rocks upward -> mushroom shaped pluton; small in size (7 miles); Black Hills, SD </li></ul>
  14. 15. Intrusive Activity <ul><li>Sills- parallel to rock layers -> like window sill </li></ul><ul><li>Dike- pluton that cuts across the grain </li></ul><ul><li>Volcanic Neck- Volcano eroded away leaving the hardened neck exposed (Devils Tower, WY) </li></ul><ul><li>Plutons are important in mountain building </li></ul><ul><ul><li>CA, West Coast, Adirondacks </li></ul></ul><ul><ul><li>Yosemite National Park- exposed granite batholith </li></ul></ul>
  15. 17. Hot Spots <ul><li>Unusually hot regions of Earth’s crust where plumes of magma rise up </li></ul><ul><ul><li>Plumes move vertically, not horizontal </li></ul></ul><ul><ul><li>Hawaii- Kilauea is over hot spot now, but Loihi is forming off Hawaii as Pacific Plate moves NW </li></ul></ul>
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