From Wikipedia, the free encyclopedia A volcano is an opening
(or rupture) in the Earth's surface or crust, which allows hot,
molten rock, ash and gases to escape from deep below the
surface. Volcanic activity involving the extrusion of rock tends
to form mountains or features like mountains over a period of
time. Volcanoes are generally found where tectonic plates pull
apart or are coming together. A mid-oceanic ridge, like the Mid-
Atlantic Ridge, has examples of volcanoes caused by "divergent
tectonic plates" pulling apart; the Pacific Ring of Fire has
examples of volcanoes caused by "convergent tectonic plates"
coming together. By contrast, volcanoes are usually not created
where two tectonic plates slide past one another. Volcanoes can
also form where there is stretching of the Earth's crust and
where the crust grows thin (called "non-hotspot intraplate
volcanism"), such as in the African Rift Valley, the European
Rhine Graben with its Eifel volcanoes, the Wells Gray-Clearwater
Volcanic Field and the Rio