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Volcanoes

Volcanoes. Volcanology: The study of volcanoes Vulcanologists: scientists who study volcanoes. Anatomy of a Volcano. Central vent: where major eruption occurs Flank vent: secondary vent Magma chamber: where magma stays until pressure forces it up the vent

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Volcanoes

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  1. Volcanoes Volcanology: The study of volcanoes Vulcanologists: scientists who study volcanoes

  2. Anatomy of a Volcano • Central vent: where major eruption occurs • Flank vent: secondary vent • Magma chamber: where magma stays until pressure forces it up the vent • Fumarole: flank vent that releases gas only

  3. A. Magma and Lava • Volcanism: any activity that includes the movement of magma towards or on the Earth's surface

  4. Magma • Magma: liquid rock - volcanic rock found below the Earth's surface; solid rock can become magma when liquid (water) is added (subduction zones)

  5. Lava: magma that erupts onto the Earth's surface Magma can flow onto Earth's surface through an opening - vent- or crack - fissure A volcanois any structure formed on Earth's surface by the vent and volcanic material that builds up around it

  6. B. Major Volcano Zones • 1. Subduction zones – a. oceanic lithosphere melts as it plunges beneath the continental plate, water added to mantle material creates magma ex. Ring of Fire b. ocean trenches where oceanic subducts under oceanic creates volcanic islands arcs ex. Aleutian Islands, AK, Japan

  7. 2. Mid-ocean ridges magma flows up through rift zone, can form underwater volcanoes ex. Iceland - MOR above sea-level; contains many fissures

  8. 3. Hot spots - in the middle of a plate is a spot where magma flows upward; plate moves over the hot spot and form a volcano; volcano is carried away by plate and become extinct ex. Hawaiian Islands • A new Hawaiian island forming underwater - Loihi

  9. C. Types of Lava • The violence of an eruption depends on: • type of magma (minerals) • temperature of the magma • The amount of dissolved gases

  10. Viscosity • viscosity - resistance to flow • More viscous - flows slowly • Less viscous - flows quickly

  11. Mafic Lava • Dark colored • Contains magnesium and iron • Makes up oceanic crust • Is hot and thin, less viscous - flows quickly - gases escape easily - "quiet flow" • ex. Hawaiian volcanoes

  12. Pahoehoe • If mafic lava cools slowly: forms wrinkly crust - pahoehoe - Hawaiian for "ropy"

  13. Aa • if it cools quickly: it forms rough, jagged chunks - aa

  14. Lava Tubes • If outer edges cool quickly and inner lava still flows: creates tunnel called lava tubes

  15. Pillow Lava • Lava flowing out of fissures on ocean floor: cools quickly & forms rounded pillow lava

  16. Felsic Lava • Is light colored • Contains silica • Makes up continental crust • Is cool and thick, more viscous - lots of trapped gases - explosive! • ex. continental volcanoes - Mt. St. Helens

  17. D. Pyroclastic material • These are rock fragments sent into the air from explosive felsic lava eruptions • They are described by size

  18. Volcanic Dust and Ash • Volcanic dust < 0.25 mm in diameter • Volcanic ash > 0.25 - 2 mm • These may travel far from the eruption!!

  19. Lapilli, Bombs and Blocks • Lapilli "little stones“ 2 - 64 mm; they fall near the vent • Volcanic bombs -clumps of lava sent spinning thru the air • Volcanic blocks - large rocks blasted from fissure; can be house-size

  20. Pyroclastic flow • The most deadly aspect to volcanic eruptions • Combination of hot, toxic gases coming from vents, up to 1000 C, and 750 km/hr • More dense than air, so rolls into villages killing victims quickly (e.g. Pompeii) • Video: http://videos.howstuffworks.com/discovery/7153-volcanoes-pyroclastic-flow-video.htm

  21. E. Volcano Typeshow do volcanoes form? http://videos.howstuffworks.com/discovery/27683-assignment-discovery-formation-of-volcanoes-video.htm

  22. 1. Shield Volcanoes • Form: when hot, mafic lava builds up around the vent - form cones • Have wide, broad bases and gently sloping sides, medium height • ex. Hawaiian Islands

  23. 2. Cinder Cone Volcanoes • Very steep sloped sides, short (few hundred meters) • Formed from layers of ash and other explosive pyroclastic materials • ex. Sunset Crater, AZ

  24. 3. Composite Volcanoes, or Stratovoclanoes • Composite means a mix of unlike things, “strato-” means layer • Formed from alternating layers of lava and ash • ex. Mt. Fuji, Mount Hood, Mt. St. Helens

  25. Crater • A pit at top of volcano, formed when material is blown out • Usually widens due to weathering and erosion • Often a smaller cone may form inside crater • When filled with water = a crater lake - Crater Lake National Park, Oregon

  26. Caldera • A large, basin shaped depression formed from a crater • If magma chamber is empty, the crater collapses - forms caldera • Also formed from huge eruptions • ex. Krakatau

  27. F. Predicting Volcanic Eruptions Scientists use the following to predict EQs: 1. seismographs monitor for small EQs from growing pressure, that often precede eruptions 2. slight bulging of surface from magma pushing out 3. change in ground tilt

  28. 4. gases • 5. history of previous eruptions • Very few volcanoes have a lengthy history to study; constant monitoring is required

  29. G. Extraterrestrial Volcanoes • Moon - was once volcanically active - evidence of lava flows • Craters - a result of bombardment by meteorites)

  30. Mars - many volcanoes and volcanic features • Olympic Mons - shield volcano - 28 km above surface, base = 600 km; probably stayed on lava source for millions years (no plate tectonics) • Still active volcanoes on Mars?? Not sure, but it is seismically active

  31. Io • Moon of Jupiter • Many active volcanoes - more eruptions; more material ejected than on Earth each month; probably sulfuric lava • Spectacular eruptions - umbrella-shaped plumes hundreds km high • Vulcanism probably caused by friction

  32. Importance of Volcanoes • all original rocks on Earth's crust were formed from cooled magma and/or lava • water vapor from volcanoes early in Earth's history may have formed oceans • gases from early eruptions formed the atmosphere • volcanism adds new crust and reshapes planet each year

  33. Supervolcanoes • What are they? http://6.cn/watch/3812360.html Several on youtube.com • ex: under Yellowstone National Park http://dsc.discovery.com/convergence/supervolcano/supervolcano.html

  34. Tsunami and landslides • Alaska: http://geology.com/records/biggest-tsunami.shtml • Volcano driven: East coast US (when ?) http://www.history.com/videos/mega-disasters-east-coast-tsunami#mega-disasters-east-coast-tsunami 10 ways the Earth will end:

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