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.
Related category GEOLOGY AND PLANETARY SCIENCE
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