Maar
A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption. A maar characteristically fills with water to form a relatively shallow crater lake, which may also be called a maar.
Maars generally range in size from across and from deep. Most maars fill 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.
Etymology
The name maar comes from a Moselle Franconian dialect word used for the circular lakes of the Daun area of Germany. The word evolved from its first use in German in the modern geological sense in 1819 and is now used in English and in the geological sciences as the term for the explosion crater, even if water from rainfall might always have drained from the crater after the formation event. This extension in meaning was due to recognising that the lake may no longer exist. Since maar lakes are formed after initially ground or subsurface water interacts with a magma intrusion to create an explosion crater, the name came to be used for the crater type as well. The present definition of the term relates to both its common and scientific discourse use in language over two centuries. Depending upon context there may be other descriptors available to use in the geological sciences such as the term tuff ring or maar-diatreme volcanoes. These last are volcanoes produced by explosive eruptions that cut deeply into the country rock with the maar being "the crater cut into the ground and surrounded by an ejecta ring". A 2011 geological clarification of a maar is "Maar volcanoes are distinguished from other small volcanoes in having craters with their floor lying below the pre-eruptive surface".Maar lakes and dry maars
Maar lakes, also referred to simply as maars, occur when groundwater or precipitation fills the funnel-shaped and usually round hollow of the maar depression formed by volcanic explosions. Examples of these types of maar are the three maars at Daun in the Eifel mountains of Germany.A dry maar results when a maar lake dries out, becomes aggraded or silted up. An example of the latter is the Eckfelder Maar. Near Steffeln is the Eichholzmaar which has dried out during the last century and is being renaturalised into a maar. In some cases the underlying rock is so porous that maar lakes are unable to form. After winters of heavy snow and rainfall many dry maars fill partially and temporarily with water; others contain small bogs or often artificial ponds that, however, only occupy part of the hollow.
Distribution
The largest known maars are found at Espenberg on the Seward Peninsula in northwest Alaska. These maars range in size from in diameter and a depth up to. These eruptions occurred in a period of about 100,000 years, with the youngest occurring about 17,500 years ago. Their large size is due to the explosive reaction that occurs when magma comes into contact with permafrost. Hydromagmatic eruptions are increasingly explosive when the ratio of water to magma is low. Since permafrost melts slowly, it provides a steady source of water to the eruption while keeping the water to magma ratio low. This produces the prolonged, explosive eruptions that created these large maars. Examples of the Seward Peninsula maars include North Killeak Maar, South Killeak Maar, Devil Mountain Maar and Whitefish Maar.Maars occur in western North America, Patagonia in South America, the Eifel region of Germany, and in other geologically young volcanic regions of Earth. Elsewhere in Europe, La Vestide du Pal, a maar in the Ardèche department of France, is easily visible from the ground or air. Kilbourne Hole and Hunt's Hole, in southern New Mexico near El Paso, Texas, are maars. The Crocodile Lake in Los Baños in the Philippines, though originally thought to be a volcanic crater, is a maar. The carbon dioxide-saturated Lake Nyos in northwestern Cameroon is another example, as is Zuñi Salt Lake in New Mexico, a shallow saline lake that occupies a flat-floored crater about across and deep. Its low rim is composed of loose pieces of basaltic lava and wall rocks of the underlying diatreme, as well as chunks of ancient crystalline rocks blasted upward from great depths. Maars in Canada are found in the Wells Gray-Clearwater volcanic field of east-central British Columbia and in kimberlite fields throughout Canada. Another field of maars is found in the Pali-Aike Volcanic Field in Patagonia, South America. and in the Sudanese Bayuda Volcanic Field. The Auckland volcanic field in the urban area of Auckland, New Zealand, has several maars, including the readily accessible Lake Pupuke in the North Shore suburb of Takapuna.
Arizona's Meteor Crater was for many years thought to be a maar of volcanic origin but it is now known to be an impact crater.
Germany
Eifel maars
In the Volcanic Eifel there are about 75 maars. Both lake-filled and dry maars are typical, though the latter are more common. The last eruptions took place at least 11,000 years ago, and many maars are older, as evidenced by their heavy erosion and less obvious shapes and volcanic features.Water-filled maars of the Eifel
| Name Geo-coordinates | Location near/between | Area in ha | Depth in m | Remarks |
| Eichholzmaar | Duppach, Steffeln | Smallest permanent Eifel maar lake | ||
| Gemündener Maar | Gemünden | |||
| Holzmaar | Eckfeld, Gillenfeld | Crossed by a stream | ||
| Immerather Maar | Immerath, Strotzbüsch | Shallowest of all Eifel maar lakes | ||
| Meerfelder Maar | Deudesfeld, Meerfeld | |||
| Pulvermaar | Gillenfeld, Immerath | Deepest and largest maar lake in Germany | ||
| Schalkenmehrener Maar | Gemünden, Schalkenmehren | |||
| Ulmener Maar | Ulmen | Most recent maar in the Eifel | ||
| Weinfelder Maar | Gemünden, Schalkenmehren | Also called the Totenmaar |
Dry maars of the Eifel
In the Eifel and Volcanic Eifel there are numerous dry maars:- Mosbrucher Weiher
- Booser Doppelmaar
- Dreiser Weiher
- Dürres Maar
- Duppacher Weiher
- Geeser Maar
- Eckfelder Maar
- Eigelbacher Maar
- Hitsche Maar
- Immerather Risch
- Gerolsteiner Maar
- Schalkenmehrener Maar E
- Schönfelder Maar
- Steffelner Laach or "Laach Maar"
- Dehner Maar
- Walsdorfer Maar
- Wollmerather Maar
Broader use of the term ''maar''
- Windsborn Crater Lake and Hinkelsmaar in the Manderscheid Volcano Group near Bettenfeld, crater lakes of the Mosenberg |Mosenberg
- Laacher See near Maria Laach, lake in a caldera of the Laacher See volcano
- Strohner Märchen, volcanic pipe which has become a maar
- Papenkaule, a volcanic crater, and the associated eruption site of the Hagelskaule
- Elfenmaar near Bad Bertrich, an almost entirely eroded stratovolcano
- Rodder Maar near Niederdürenbach, the origin of which is unclear
Maars outside the Eifel
Rest of Europe
The Chaîne des Puys in France contains numerous maars; Lake Albano in the Alban Mountains is a complex maar, and there is also a submarine maar near Santorini in Greece. The Campo de Calatrava Volcanic Field in Spain contains numerous maars; a typical example being the maar of Hoya del Mortero at Poblete in the Province of Ciudad Real.Active maars were commonplace in Fife and Lothian, Scotland during the Carboniferous period. The location of one such maar was Elie Ness.
Americas
Active maar volcanoes are mainly known outside Europe.In the US there are numerous maar areas, such as in Alaska ; in Washington ; in Oregon ; in Death Valley National Park, California ; in Nevada ; as well as the maars of the White Rock Canyon, Mount Taylor, the Potrillo volcanic fields, and Zuñi Salt Lake in New Mexico.
In Central Mexico, the Tarascan volcanic field contains several maars in the states of Michoacán and Guanajuato. The Río Cuarto and Hule maars are in Costa Rica. In Nicaragua is the maar of Laguna de Xiloa, part of the Apoyeque volcano. From South America, there are known maars in Chile. Jayu Khota is a maar in Bolivia.