Volcanoes Def: A rupture on the crust of a planetary-mass object, such as earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
Causes *the crust is broken into 17 major tectonic plates that float on a hotter, softer layer in its mantel. *volcanoes generally are found where tectonic plates are diverging or converging. *magma rises through cracks or weaknesses in the earths crust, when this pressure is released, as a result of plate movement, magma explodes to the surface causing a volcanic eruption.