Volcanoes

• Two types

  Shield Volcano, Stratovolcano
• Shield Volcano

  gentle slopes, low viscous lava, travels far, wide base to volcano, made up of layers of lava from gentle slopes
• Stratovolcano

  Ash covers large areas, complex shape due to landslips and explosion damage, caldera caused by collapse of top of volcano, volcanic domes from viscous lava, narrow base, explosive eruptions, layers of lava and ash build up volcano
• Shield Volcanic Hazards

  Lava flows, small amount of ash, volcanic gas
• Stratovolcano Hazards

  Explosive, pyroclastic material, pyroclastic flow, Lahar, landslides
• Stratovolcanoes


  Over 60% of Earths individual volcanoes.

  Eruptions can last hours, days or years
• They have Eruptive Cycles:

  1. A period of no activity - magma and gas pressure builds up in the magma chamber
  2. Once pressure exceeds the weight of overlying rock there will be an explosion, this blasts away the top of the volcano - allows pyroclastic material to escape
  3. Lava reached the surface and forms a layer on top of the pyroclasts. As gas pressure decreases the lava supply cools and plugs the vent
• Caldera


  A large circular depression caused by violent explosions followed by the collapse of the top of a volcanic cone
• Magma Chamber


  Small chamber = small explosion

  Large chamber = large explosion
• Geysers and Hot Springs


  Occur if vent is constricted - allowing pressure to build.

  Common in volcanic areas as ground water is heated by magma

  Convection causes it to rise. which builds pressure resulting in the water exploding upwards

  It then drains back into the ground and the cycle repeats