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Volcanoes - PowerPoint PPT Presentation

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Volcanoes. Volcanoes. Magma formation. Magma formation is influenced by depth, pressure, temperature, and the presence or absence of water (which influences melting point). Three major igneous rock types, basalt, andesite , and rhyolite , form three corresponding types of magma.

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magma formation
Magma formation
  • Magma formation is influenced by depth, pressure, temperature, and the presence or absence of water (which influences melting point).
  • Three major igneous rock types, basalt, andesite, and rhyolite, form three corresponding types of magma.
  • Different magmas have different viscosities, which influences their behavior
basaltic magma
Basaltic magma
  • Forms when rocks in the upper mantle melt
  • Low viscosity
  • Rises quickly to surface and reacts little with crustal rocks
  • Contains small amounts of dissolved gases and silica, so erupts quietly
andesitic magma
Andesitic magma
  • Found along continental margins, where oceanic crust is subducted into Earth’s mantle
  • Source for magma can be either oceanic crust or oceanic sediments
  • Contains about 60% silica (vs. 50% for basaltic magma), so is more explosive and more viscous
rhyolitic magma
Rhyolitic magma
  • Forms when molten material rises and mixes with overlying silica- and water-rich continental crust
  • High viscosity inhibits its movement
  • Resistance to flow + lots of gas trapped inside it make it very explosive
magma that cools within the earth is called a pluton
Magma that cools within the Earth is called a PLUTON
  • Batholiths: the largest plutons, cover ≥ 100km2. Found in the interiors of major mountain chains. Mostly made of granite.
  • Stocks: irregularly-sized plutons that are smaller than batholiths
  • Laccoliths: mushroom-shaped plutons (rock bows upward as a result of intense heat and pressure of magma body)
  • Sills: plutons that form when magma intrudes parallel to layers of rock
  • Dikes: plutons that cut across preexisting rock
types of volcanoes
Types of Volcanoes
  • A shield volcano is circular, with gently sloping sides. Layers of lava accumulate during non-explosive eruptions. Thus, formed of basaltic lava
  • A cinder cone volcano is made of more viscous magma. Explosions rocket material high into the air. It piles up around the vent.
  • A composite volcano forms when layers of volcanic pieces alternate with lava. Larger than cinder cone volcanoes; potentially dangerous.
where do volcanoes occur1
Where do volcanoes occur?
  • Divergent boundaries
where do volcanoes occur2
Where do volcanoes occur?
  • Hot spots, either on land or at sea (more common)
what about yellowstone
What about Yellowstone?
  • http://www.dailymail.co.uk/sciencetech/article-1350123/Worlds-largest-volcano-Yellowstone-National-Park-wipe-thirds-US.html
  • Is it likely to erupt?
  • What kind of volcano is it?
  • Why would there be a volcanic eruption in the continental interior?