Volcanoes

• Shield volcanoes


  • Form at divergent boundaries
  • As plates move apart, magma rises through the gap
  • The magma is basalt, and is thin and runny, meaning that it can create extensive lava flows
  • Small earthquakes occur at the plates boundary, but tend to be not violent
• Hot spot volcanoes


  • Can form in the middle of plates
  • Occur when a plume of hot magma rises to the surface and breaks through the crust
  • When this happens, there is an eruption and a volcano forms
  • Hotspots remain stationary over time, but as the crust moves above them, chains of volcanoes can form
  • Hawaii is a chain of volcanic islands
• Composite volcanoes


  • Form at convergent plate boundaries
  • Oceanic plate moves under the continental plate, as it more dense
  • The oceanic plate is subducted into the mantle, where it is melted and destroyed, creating magma called andesite
  • Sea water is dragged down with it
  • Magma rises as plumes upwards through the continental crust, along with steam, making the volcanoes explosive
  • Ash, volcanic bombs, pyroclasic flows and viscous lava are erupted
  • Earthquakes are common and can be devastating
• Characteristics of steep sided volcanoes


  • Explosive eruptions
  • VEI 4-5
  • Andesitic lava
  • Lava is viscous and sticky
  • Violent earthquakes
• Characteristics of gentle sloped volcanoes


  • Eruptions are frequent yet non explosive
  • VEI 1
  • Basaltic lava
  • Lava is hot and runny
  • Regular small earthquakes