Volcanoes

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Destructive plate margins

  • An oceanic plate and a continental plate move towards each other
  • The denser oceanic plate subducts under the continental plate
  • The oceanic plate is melted in the magma under the crust and a pool of magma forms
  • The magma erupts through 'vents' in the surface to form a volcano
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Constructive plate margin

  • Two plates move away from each other
  • Magma rises up into the gap that is formed between the two plates, forming new crust or a volcano
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Composite volcanoes

  • Found at destructive margins
  • Eruptions may be a pyroclastic flow - hot steam, ash, rock and dust
  • Eruptions infrequent but often violent
  • Steep-sided
  • Made of layers of ash and lava, that have erupted, cooled and hardened
  • The lava is thick, flows slowly and hardens quickly

 

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Shield volcanoes

  • Found at constructive margins
  • Eruptions are frequent but gentle
  • Low and flat
  • Made up of only layers of lava
  • The lava is runny and spreads over a wide area

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