Volcanic pipes orvolcanic conduits are subterraneangeological structures formed by the violent,supersonic eruption of deep-originvolcanoes. They are considered to be a type ofdiatreme. Volcanic pipes are composed of a deep, narrow cone of solidifiedmagma (described as "carrot-shaped"), and are usually largely composed of one of two characteristic rock types —kimberlite orlamproite. These rocks reflect the composition of the volcanoes' deep magma sources, where the Earth is rich inmagnesium. They are well known as the primary source ofdiamonds, and are mined for this purpose. Volcanic pipes are relatively rare by this definition based on minerals and depth of the magma source, but on the other hand volcanic diatremes are common, indeed the second commonest form of volcanic extrusion (that is magma that reaches the surface).
Volcanic pipes form as the result of violent eruptions of deep-origin volcanoes.[1] 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 andvolatile compounds such aswater andcarbon dioxide. As the body of magma rises toward the surface, the volatile compoundstransform togaseous phase aspressure is reduced with decreasing depth. This sudden expansion propels the magma upward at rapid speeds, resulting in a supersonicPlinian eruption.
Inkimberlite pipes, the eruption ejects a column of overlying material directly over the magma column, and does not form a large above-ground elevation as typical volcanoes do; instead, a low ring ofejecta known as atuff ring forms around a bowl-shaped depression over the subterranean column of magma. Over time, the tuff ring may erode back into the bowl, leveling out the depression by filling it with washed-back ejecta.Kimberlite pipes are the source of most of the world's commercial diamond production, and also contain other preciousgemstones and semi-precious stones, such asgarnets,spinels, andperidot.
Lamproite pipes operate similarly to kimberlite pipes, except that the boiling water and volatile compounds contained in the magma actcorrosively on the overlying rock, resulting in a broader cone of eviscerated rock (the ejection of this rock also forms a tuff ring, like kimberlite eruptions). This broad cone is then filled with volcanic ash and materials. Finally, the degassed magma is pushed upward, filling the cone. The result is a funnel shaped deposit of volcanic material (both solidified magma, and ejecta) which appears mostly flat from the surface.
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