VOLCANOES CHAPTER 10

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VOLCANOES CHAPTER 10
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• Viscosity the resistance to the flow. As
  temperature decreases, viscosity increases.
• As silica content increases, viscosity increases.
  Therefore, continental (rhyolitic) volcanoes
  with high silica content are more explosive than
  basaltic volcanoes.

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• Dissolved Gases
• Dissolved gas (mostly water vapor and carbon
  dioxide) comes out of solution as the pressure
  decreases near the Earths surface.
• Continental eruptions are explosive because of
  the trapped gas. Basaltic eruptions like Hawaii,
  the gases escape and the lava flows quietly.

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• Volcanic Material
• Lava Flows
• Continental volcano lava, with high silica
  content flows slowly.
• Basaltic volcano lava, like Hawaii, flows
  quickly. Types of lava flows are pahoehoe and
  aa.

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• Gases emitted by volcanoes are water vapor,
  carbon dioxide, nitrogen, sulfur, chlorine,
  hydrogen, and argon.

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• Pyroclastic material are fragments ejected during
  volcanic eruptions. Types of pyroclastic
  material include ash, cinders(lapelli), blocks,
  and bombs.

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• Anatomy of a Volcano
• Crater, Vent, Volcano

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• Shield volcanoes produced by the accumulation
  of basaltic lava, examples are Hawaiian Islands
  and Iceland

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• Cinder cones steep sloped, small, eruptions
  last only a short time

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• Composite cones located along the Pacific Ring
  of Fire, examples are volcanoes in the Cascade
  region of the Pacific Northwest and the Andes
• Large, silica-rich, most explosive eruption

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• Dangers from Composite ones
• Pyroclastic flows
• Lahars mudflows of volcanic material

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• Volcanic Landforms
• Calderas large depression in a volcano, formed
  by a collapse of a crater
• Crater Lake is in a caldera
• Necks and pipes - formed from hardened magma in
  vents
• Lava Plateaus formed from successive lava flows
  extruded by fissures over a large area

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• Intrusive Igneous Bodies Plutons
• Sills forms when magma is injected along
  sedimentary bedding planes
• Laccoliths more viscous lava injected along
  sedimentary bedding planes
• Dikes form when magma is injected into
  fractures
• Batholiths largest intrusive igneous body,

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• Origin of Magma Geologists conclude that magma
  originates when essentially solid rock, located
  in the crust and upper mantle, partially melts.
• Source of heat to melt rocks temperatures get
  higher with depth, 20 to 30 degrees Celsius per
  kilometer. Additional heat is generated by
  friction and rising magma
• Reducing pressure lowers a rocks melting
  temperature
• Water causes a rock to melt at a lower
  temperature.

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• Most volcanoes are located along the margins of
  the ocean basins at oceanic-continental
  convergent plate boundaries. As the oceanic
  plate subducts the continental crust, some rock
  melts. The magma rises, forming silica-rich
  volcanoes.

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• At oceanic-oceanic convergent plate boundaries a
  chain of volcanoes, volcanic arcs form.

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• At divergent boundaries, magma is produced along
  ridges during sea floor spreading.

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• Interplate igneous activity is associated with
  mantle plumes, or hot spots. Examples are
  Hawaiian Islands

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