Diatremes and Maars

lake and tundra
Devil Mountain Maar, Bering Land Bridge National Preserve, Alaska.
Diatreme is a general term used to describe a volcanic vent or pipe that formed when magma was forced through flat-lying sedimentary rock. The explosive energy of magmas with high dissolved gas contents allowed the magma to be forced through the rocks to form an expanded vent. The sedimentary rock around the vent is lithified (melted together) and small amounts of magma intrude into the rock.

Phreatic eruptions are also associated with diatremes. These steam-driven explosions occur when groundwater is heated by nearby magma, lava or volcanic deposits. The intense and high temperatures of these materials cause water to boil or flash to steam, leading to explosive eruptions of steam, ash, and other volcanic material.

illustration of maar explosion
Illustration of maar explosion from Bandelier National Monument geologic report. Source: Trista L. Thornberry-Ehrlich, Colorado State University.
Maars are shallow, low-relief craters with flat floors. They often fill with water, forming natural lakes. It is typical for maars to form over diatremes. The walls of a maar are a combination of fragmented volcanic rock, and fragments of the underlying diatreme.

It is not unusual to find minerals and ores mined around diatremes. For example, the kimberlite pipes in South Africa are diatremes that have abundant diamonds. Also, it is not uncommon to find gold and silver mines around diatremes.

Volcanism in Parks—Diatremes and Maars

Bandelier National Monument, New Mexico

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Bering Land Bridge National Preserve, Alaska

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Katmai National Park and Preserve, Alaska

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Last updated: February 21, 2019