Formation of a Volcano

Magma is formed by high temperatures and pressure. The magma forms at depths of 80 to 160 kilometers beneath the earth's surface. The magma, often filled with gas, rises to the earth's surface because it is less dense then the solid rock. As it rises, it forms a large chamber, melting surrounding rock, as close as 3 kilometers to the surface. This magma chamber contains the volcanic materials.

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