Volcano monitoring involves a variety of measurements and observations designed to detect changes at the surface of a volcano that reflect increasing pressure and stresses caused by the movement of magma, or molten rock, within or beneath it. An eruption occurs when magma rises from its source or from a storage reservoir and finally reaches the Earth's surface. As it rises, the magma fractures overlying rocks, which causes earthquakes, and parts of the volcano deform as magma approaching the surface makes room for itself. -- Excerpt from: Brantley and Topinka, 1984 |