IE 3.1 Notes: Volcanoes and Plate Tectonics

• Volcano


  A weakness in the crust where molten material, or magma, comes to the surface
• Magma


  A molten mixture of rock forming substances, gases, and minerals from the mantle
• Lava


  Magma that reaches the surface
• Lava cools and hardens

  Forming solid rock = more crust
• Where volcanoes are found

  • Most volcanoes form on plate boundaries that extend across continents and oceans
  • 75% of the world's active volcanoes found in volcanic belts
• What causes volcanoes


  At plate boundaries, crust can either diverge or converge, causing the crust to fracture or break, allowing magma to come through that break
• Volcanoes formed at divergent boundaries

  • Undersea: mid ocean ridges
  • Continental: Great rift valley
• Volcanoes formed at convergent boundaries

  • Oceanic crust subducts under continental crust, often causing magma to reach the surface
  • Oceanic crust subducts under oceanic crust, the subducted plate melts and forms magma which rises to the surface, forming an island arc
• Island arcs


  • Japan
  • New Zealand
  • Caribbean