Causes of volcanic eruptions

Key things you should know about volcanoes:

1. A volcano is formed by eruptions of lava and ash.
2. Volcanoes are usually cone shaped mountains or hills.
3. When magmamagma: Magma is the hot molten rock found beneath the surface of the Earth. It reaches the surface through volcanic activity and forms the basis of igneous rocks. reaches the Earth's surface it is called lava. When the lava cools, it forms rock.
4. Volcanic eruptions can happen at destructivedestructive boundaries: Crustal plate boundaries that converge (come together) with each other. May also be referred to as subduction zones. and constructiveconstructive boundaries: Constructive boundaries exist between two crustal plates that are moving away from each other, causing new crustal rocks to form. May also be referred to as divergent plate boundaries. boundaries, but not at conservative boundariesconservative boundaries: Conservative boundaries are areas between two crustal plates that are moving past each other in opposite directions. Crust is neither created nor destroyed..
5. Some volcanoes happen underwater, along the seabed or ocean floor.

How volcanoes form

Krakatoa in the Sunda Strait, Indonesia

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