The Volcanoes...

A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, volcanic ash and gases to escape from the magma chamber below the surface. Volcanoes are generally found where tectonic plates are diverging or converging. 

for more information visit: 

http://en.wikipedia.org/wiki/Volcano

information take of:

 http://en.wikipedia.org/wiki/Volcano