Volcanoes: Distribution and Frequency AQA Geography

Overall summary of volcanoes. Where they can be found? What types of volcanoes are produced due to the plate margins? And what are the impacts of volcanic activity?

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  • Volcanoes
    • Distribution
      • Volcanic activity is found usually along plate margins where the oceanic plate is being destroyed. Otherwise known as subduction. Where the oceanic plate is being subducted in the benioff zone, magma is forced upwards creating vicious in nature eruptions.
      • Volcanoes occur along at oceanic ridges where plates are pulling apart forcing magma to rise and effectively 'patch' the crust.
      • Rift Valleys, volcanoes occur here. Continental plates are pulling apart.
      • Hot Spots. this where a pulme of magma penetrates the crust (lithosphere). It is stationary and does not move, so only the volcano above it is active. Consists of radioactive elements.
    • Frequency
      • Constructive Plate Margins produce shield volcanoes or lava plateaux. Meaning eruptions are fairly frequent yet are not violent in nature. The lava type is Basaltic and is slow in silica.
      • Destructive plate margins produce composite volcanoes that consist of ash and lava in layers. The lava is Rhyolite and has high content in silica. Because of this, the eruptions are less frequent however more vicious in nature.
    • Impact of Volcanic Activity
      • Tephra: solid material of varying grain size that is ejected as ash bombs into the atmosphere.
      • Pyroclastic Flows: Very hot (800c) gas charged, high-velocity flows
      • Lava Flows: What it says on the tin.
      • Volcano gases such as carbon dioxide, monoxide, sulphur ect.
      • Lahars: Volcanic mud flows
      • Flooding: Melting glaciers and ice caps
      • Tsunamis
      • Volcanic landslides
      • Climate Change: reduce global temperatures


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