magma

^{ALASKA VOLCANO OBSERVATORY GLOSSARY}

Molten rock beneath the Earth's surface.

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^{GLOSSARY OF VOLCANIC TERMS}

A term used to describe subsurface molten rock (Jeanloz, 2000, p. 41). Magmas are generally considered to be silicate melts (Grove, 2000, p. 133; Wallace and Anderson, 2000, p. 149), but may also be composed of carbonatitic liquids (Spera, 2000, p. 171). Magmas are composed of up to three components (liquid, crystalline solids, and gas (or supercritical fluid) bubbles; Grove, 2000, p. 133), and may be fully liquid or partially crystalline. Lavas are magmas that have erupted on to a planet's surface.

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^{USGS PHOTO GLOSSARY OF VOLCANIC TERMS}

Magma is molten or partially molten rock beneath the Earth's surface. When magma erupts onto the surface, it is called lava. Magma typically consists of (1) a liquid portion (often referred to as the melt); (2) a solid portion made of minerals that crystallized directly from the melt; (3) solid rocks incorporated into the magma from along the conduit or reservoir, called xenoliths or inclusions; and (4) dissolved gases.

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Sketch by B. Myers

This sketch shows a classic cartoon view of a magma reservoir beneath a volcano and a conduit leading up to a lava dome at the surface. The arrow indicates direction of magma movement from a deeper source.