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Volcanic pipe
Volcanic pipes are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes. They are considered to be a type of ''diatreme''. Volcanic pipes are composed of a deep, narrow cone of solidified magma (described as "carrot-shaped"), and are usually largely composed of one of two characteristic rock types — kimberlite or lamproite. These rocks reflect the composition of the volcanoes' deep magma sources, where the Earth is rich in magnesium. Volcanic pipes are relatively rare. They are well known as the primary source of diamonds, and are mined for this purpose.
==Formation==
Volcanic pipes form as the result of violent eruptions of deep-origin volcanoes. These volcanoes originate at least three times as deep as most other volcanoes, and the resulting magma that is pushed toward the surface is high in magnesium and volatile compounds such as water and carbon dioxide. As the body of magma rises toward the surface, the volatile compounds transform to gaseous phase as pressure is reduced with decreasing depth. This sudden expansion propels the magma upward at rapid speeds, resulting in a shallow supersonic eruption. A useful analogy to this process is the uncorking of a shaken bottle of champagne.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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