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Volcanic pipe

2007 Schools Wikipedia Selection. Related subjects: Geology and geophysics

   Volcanic Pipe
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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 warm or shaken bottle of
   champagne.
   The Crater, Hypipamee National Park, Atherton Tableland, Queensland,
   Australia. This residue of a pipe is about 100m across.
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   The Crater, Hypipamee National Park, Atherton Tableland, Queensland,
   Australia. This residue of a pipe is about 100m across.

Kimberlite pipes

   In kimberlite 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 of ejecta known
   as a tuff 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.

Lamproite pipes

   Lamproite pipes operate similarly to kimberlite pipes, except that the
   boiling water and volatile compounds contained in the magma act
   corrosively 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 martini-glass shaped deposit
   of volcanic material (both solidified magma, and ejecta) which appears
   mostly flat from the surface.

   Retrieved from " http://en.wikipedia.org/wiki/Volcanic_pipe"
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