Volcanoes

• Destructive plate boundaries


  • Oceanic plate moves down into the mantle, where it is melted and destroyed (due to it being more dense)
  • A pool of magma forms
  • The magma rises through cracks called vents
  • Magma erupts onto the surface forming a volcano
• At constructive margins the magma rises up into the gap created by plates moving apart, forming a volcano
• When volcanoes erupt they emit lava and gases. Some volcanoes emit lots of ash which can:

  • cover land,
  • block out the sun
  • form pyroclastic flow (super-heated currents of gas, ash and rock)
• Hotspot


  A bit of the Earth's crust is hotter than normal. They occur where a plume of hot magma from the mantle moves towards the surface. There is an eruption and a volcano forms.

  They can be both Oceanic and continental
• Hotspots remain stationary over time, but the curst moves above them. This creates chains of volcanic islands e.g., Hawaii
• Composite volcanoes e.g., Mount Fuji


  • Occur at destructive plate boundaries
  • Subducted oceanic crust contains lots of water and this can cause the subducted crust to erupt
  • Eruptions start with ashy explosions then deposit a layer of ash
  • Then erupt a layer of thick, sticky lava that can't flow far
• Shield volcanoes


  • Occur at hotspot or constructive plate boundaries
  • Not bery explosive and only made of lava
  • Lava is runny and flows quickly
  • Spreads over a wide area, forming a low, gentle-sided volcano