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volcanism





Also called vulcanicity, the processes whereby magma, a complex of molten silicates containing water and other volatiles in solution, rises toward the Earth's surface, there forming igneous rocks. These may be extruded on the Earth's surface (see lava; volcano) or intruded into subsurface rock layers as, for example, dikes, sills, and laccoliths,

On icy moons the phenomenon is sometimes called cryovolcanism to distinguish it from silicate or sulfur volcanism.


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   • GEOLOGY AND PLANETARY SCIENCE