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.
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 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.
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.
*
Udachnaya pipe, a diamond mine in Yakutia, Russia
* American Museum of Natural History.
"The Nature of Diamonds". Retrieved March 17, 2005.
* Tilling (1985).
"Volcanoes" (excerpt). United States Geological Survey: Special Interest Publication. Retrieved March 17, 2005.
