Volcanoes form when magma reaches the Earth's surface, causing eruptions of lava and ash. They occur at destructive (compressional) and constructive (tensional) plate boundaries.

The immediate effects of volcanic eruptions can be devastating, but they may be beneficial in the long term.

Key facts

• 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…