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Photo glossary of volcano terms

Aerial view of east Ukinrek Maar, Alaska

Photograph by C. Nye on 9 May 1994
Alaska Division of Geological and Geophysical Surveys

Phreatic and magmatic explosive eruption of Ukinrek Maars, Alaska

Photograph by R. Russell on 6 April 1977
Alaska Department of Fish and Game
 Maar
A maar is a low-relief, broad volcanic crater formed by shallow explosive eruptions. The explosions are usually caused by the heating and boiling of groundwater when magma invades the groundwater table. Maars often fill with water to form a lake.

 

Top photo: Aerial view toward N of Ukinrek Maars, Alaska; Lake Becharof at top of photo. Water partially fills the eastern maar and completely covers a lava dome that was erupted in the 100-m deep crater during a 10-day eruption in 1977. Maar is about 300 m in diameter.

Bottom photo: Eruption column generated by phreatic and magmatic explosions rises from the larger east maar.

Related photo glossary terms:

 

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U.S. Department of the Interior, U.S. Geological Survey, Menlo Park, California, USA
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Last modification: Monday, 04-Sep-2000 22:44:26 EDT (SRB)