Formation of Volcanoes

he Earth has volcanoes because it is hot inside. In some places, it is hot enough to melt solid rock and turn it into liquid rock. This liquid rock is called magma. The magma rises toward the surface because it is less dense than the surrounding rock. If the magma reaches the surface, it is called lava. This lava accumulates and forms a volcano.

Volcanoes grow by intrusion and extrusion. Intrusion is when magma moves up into a volcano and stops, not even erupting. This causes the volcano to grow from the inside. An extrusion is an eruption that adds layers of lava and/or ash to the volcanoes exterior. This causes the volcano to grow from the outside.

Volcanoes erupt because of density and pressure. Because the magma has lower density, it rises to the surface or to a depth determined by the density of the magma and the weight of the rocks above it. As the magma rises, bubbles form from gas dissolved the magma. The bubbles exert pressure. This pressure helps the magma rise to the surface and forces it to explode into the air.

This is how a volcano forms.

Source (exerpt from Ask a Vulcanologist - Volcano World)

dantespeak explanation: Theory and Process

• See dantespeak.com Questions

Source (Dante's Peak)
Copyright 1998 Leatherman and Hofker Enterprises