Maar

A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. The maar typically fills with water to form a relatively shallow crater lake. The name comes from a local Palatinate German dialect of Daun, which is in turn derived from Latin "mare" (sea). Maars are shallow, flat-floored craters that scientists interpret as having formed above diatremes as a result of a violent expansion of magmatic gas or steam; deep erosion of a maar presumably would expose a diatreme. Maars range in size from 60 meters (200 ft) to 2000m (6,500ft) across and from 10 meters (30ft) to 200 meters (650ft) deep, and most are commonly filled with water to form natural lakes. Most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme.

Maars occur in western North America, in the Eifel region of Germany (where they were originally described), and in other geologically young volcanic regions of Earth. Kilbourne Hole and Hunt's Hole, near El Paso, Texas, are maars. The notorious, carbon dioxide-saturated Lake Nyos in Africa is another example. An excellent example of a maar is Zuni Salt Lake in New Mexico, a shallow saline lake that occupies a flat-floored crater about convert|6500|ft|m|-1 across and convert|400|ft|m|-1 deep. Its low rim is composed of loose pieces of basaltic lava and wallrocks (sandstone, shale, limestone) of the underlying diatreme, as well as random chunks of ancient crystalline rocks blasted upward from great depths. The only maar-like volcano known in Canada is found in the Wells Gray-Clearwater volcanic field in east-central British Columbia. [ [http://gsc.nrcan.gc.ca/volcanoes/type_e.php Volcanoes of Canada] - Types of volcanoes. Retrieved on 2007-10-14]

One of the most famous misidentified maars is Meteor Crater in Arizona that for many years was thought to be of a volcanic rather than meteorite origin.. [ [http://www.barringercrater.com/science/ The Science: What is the Barringer Meteorite Crater?] ]

References

* [http://volcanoes.usgs.gov/Products/Pglossary/maar.html USGS Photo glossary of volcano terms: Maar]
* [http://vulcan.wr.usgs.gov/Glossary/Maars/description_maars.html USGS: Maars and Tuff Cones]

External links

* [http://volcanodb.com/volcanoes/Maar/ List of Maar Volcanoes]
* [http://volcano.und.edu/vwdocs/volc_images/north_america/morale_claim.html Morale Claim Maar, Arizona]