Why do Volcanoes occur?
Volcanoes occur when the Earth's plates pull apart causing magma to rise to the surface. Volcanoes can also occur over hotspots and where one plate dives beneath another, forcing magma to rise to the surface. Plates diving under one another is known as subduction.
Where do Volcanoes occur?
Volcanoes usually occur on the edges of plates, similar to where earthquakes occur. A lot of volcanoes occur in the area around the edge of the Pacific ocean called the Pacific Ring of Fire. Volcanoes can also occur in the middle of plates, in hotspots. One such hotspot has formed the Hawaiian islands chain. As the earth rotated, it passed over the hotspot and new islands were formed.
(Readers Digest, Natural Disasters, 1996)
Mt St Helens
The Ring of Fire