A diatreme, sometimes known as a maar-diatreme volcano, is a volcanic pipe formed by a gaseous explosion. When

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...

rises up through a crack in

Earth's crust Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...

and makes contact with a shallow body of

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit ...

, rapid expansion of heated

water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous p ...

and

volcanic gas Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities (vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from lava, from volcani ...

es can cause a series of explosions. A relatively shallow crater (known as a ''

maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallo ...

'') is left, and a rock-filled fracture (the actual diatreme) in the crust. Diatremes breach the surface and produce a steep, inverted cone shape. The term ''diatreme'' has been applied more generally to any concave body of broken rock formed by explosive or hydrostatic forces, whether or not it is related to

volcanism Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called a ...

. The word comes .

Global distribution

Maar-diatreme volcanoes are not uncommon, reported as the second most common type of volcano on continents and islands. Igneous intrusions cause the formation of a diatreme only in the specific setting where groundwater exists; thus most igneous intrusions do not produce diatremes. Examples of diatremes include the Blackfoot diatreme and Cross diatreme in British Columbia, Canada.

Economic importance

Diatremes are sometimes associated with deposition of economically significant mineral deposits such as kimberlite magma, which originates in the upper mantle. When a diatreme is formed due to a kimberlite intrusion, there is a possibility that diamonds may be brought up, as

diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, b ...

s are formed in the upper mantle at depths of 150-200 kilometers. Kimberlite magmas can sometimes include chunks of diamond as

xenolith A xenolith ("foreign rock") is a rock fragment ( country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ig ...

s, making them economically significant.

References

Kimberlite Emplacement Models

*[https://web.archive.org/web/20130630050637/http://geosurvey.state.co.us/geology/igneousrocks/PlutonicIgneousRocks/KimberliteDiatremes/Pages/KimberliteDiatremes.aspx ''Kimberlite Diatremes,'' Colorado Geological Survey, 10-17-2012]
Lorenz, Volker, ''Maar-Diatreme Volcanoes, their Formation, and their Setting in Hard-rock or Soft-rock Environments,'' Geolines, v. 15, 2003, pp. 72-83

External links

{{commons category, Diatremes Volcanism