Key facts about volcanoes

  • A volcano is formed by eruptions of lava and ash.
  • Volcanoes are usually cone shaped mountains or hills.
  • When magma reaches the Earth's surface it is called lava. When the lava cools, it forms rock.
  • Volcanic eruptions can happen at destructive and constructive boundaries, but not at conservative boundaries.
  • Some volcanoes happen underwater, along the seabed or ocean floor.

How is a volcano formed?

Krakatoa volcano in the Sunda Strait
Krakatoa volcano in the Sunda Strait, Indonesia
  • Magma rises through cracks or weaknesses in the Earth's crust.
  • Pressure builds up inside the Earth.
  • When this pressure is released, eg as a result of plate movement, magma explodes to the surface causing a volcanic eruption.
  • The lava from the eruption cools to form new crust.
  • Over time, after several eruptions, the rock builds up and a volcano forms.