Magma be stored in magma chambers or trans-crustal crystal-rich mush zones. During their storage in the crust, magma compositions may be modified by fractional crystallization, contamination with crustal melts, magma mixing, and degassing. Following their ascent through the crust, magmas may feed a volcano or solidify underground to form an intrusion (e.g., an igneous dike or a sill). While the study of magma has historically relied on observing magma in the form of lava flows, magma has been encountered in situ three times during geothermal drilling projects—twice in Iceland (see Magma usage for energy production), and once in Hawaii. Most magmatic
Plateau upwelling of volcanic magma, extrusion of lava, and erosion by water and glaciers. Volcanic plateaus are produced by volcanic activity. The Columbia Plateau in the northwestern United States is an example. They may be formed by upwelling of volcanic magma or extrusion of lava. The underlining mechanism in forming plateaus from upwelling starts when magma rises from the mantle, causing the ground to swell upward. In this way, large, flat areas of rock are uplifted to form a plateau. For plateaus formed by extrusion, the rock is built up from lava spreading outward from cracks and weak areas in the