Extrusive Volcanic Landforms

Refers to AQA A2 Geography (Plate Tectonics and Assosiated Hazards)

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  • Extrusive Volcanic Landforms
    • Involves two forms of lava...
      • Basaltic Lava
        • Formed by lava low in silica, making for more fluid magma that allows gas bubbles to expand on the way up to the surface.
          • Prevents sudden explosive activity.
      • Andesetic and Rhyolitic Lavas
        • Formed from silica-rich (acid) magma that is very viscous.
          • Often solidifies before reaching the surface, leading to a build up of pressure and violent explosion.
    • Lava Plateaux
      • Formed by fissure eruptions.
      • Extensive lava flows are basaltic, so flows great distances.
      • Usually flat and featureless, such as the Antrim Lava Plateaux, Northern Ireland.
    • Basic/ Shield Volcanoes
      • Formed from free-flowing lava.
      • The resulting volcanoes have gentle sides and cover a large area.
      • Mauna Loa, Hawaii, is an example.
    • Ash and Cinder Cones
      • Formed from ash, cinders and volcanic bombs ejected from the crater.
      • Steep, symetrical sides.
      • Paricutin, Mexico is an example.
    • Acid/ Dome Volcanoes
      • Steep sided convex cones consisting of viscous lava, probably rhyolite.
      • Best examples in the Puy regions of central France.
    • Composite Cones
      • The classic, pyramid-shaped, volcanoes.
      • Consist of layers of ash and lava that are usually andesetic
      • Mt. Etna, Sicily, is a good example.
    • Calderas
      • Occur when the build up of gas becomes extreme and a huge explosion removes the summit of the cone.
        • Leaves an opening several kilometres in diameter.
      • May be floided by sea, or a lake may form within it.
      • Examples include Krakatoa in Indonesia and Santorini in Greece.


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