Powerful forces within the earth cause volcanoes. Scientists do not fully understand these forces but have developed theories on how the forces create volcanoes

A volcano begins as magma which is melted rock from deep within the earth. Magma is a result of the extreme heat of the earth's interior. Because the heat is so intense it partly melts the rock. When the rock melts, it produces gas which mixes with the magma. Most magma forms from 37 to 100 miles below the earth's surface. The magma and gases then rise to the surface because it is lighter than the solid rock around it. As it rises, it melts gaps in the rock and forms a magma chamber otherwise know as the magma reservoir from which volcanic materials erupt.

The volcano erupts when the gas-filled magma in the reservoir is under pressure from the weight of the solid rock