mud volcano

^{ALASKA VOLCANO OBSERVATORY GLOSSARY}

A mud volcano is a small volcano-shaped cone of mud and clay, usually less than 1-2 m tall. These small mud volcanoes are built by a mixture of hot water and fine sediment (mud and clay) that either (1) pours gently from a vent in the ground like a fluid lava flow; or (2) is ejected into the air like a lava fountain by escaping volcanic gas and boiling water. The fine mud and clay typically originates from solid rock--volcanic gases and heat escaping from magma deep below turn groundwater into a hot acidic mixture that chemically changes the rock into mud- and clay-sized fragments.

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^{USGS PHOTO GLOSSARY OF VOLCANIC TERMS}

In volcanic regions, mud volcanoes are usually small volcano-shaped cones of mud, usually less than 1-2 m tall as shown in this image. They are built as mud erupts from a vent, either as as a flowing liquid or ejected into the air. The mud is formed as acid gases rise through the crust, react with rock and turn it into clay. The mud is a mixture of clay and groundwater. The mud volcanoes erupt following pressurization from geothermal steam and gases.

Mud volcanoes can also form in non-volcanic areas. They form where subsurface layers of fluidized sediments, like silt and clay, have been pressurized by tectonic activity, such as at the boundaries of the Earth's crustal plates. They can also form by the accumulation of hydrocarbon gases. The pressurized sediment is forced upward, where it erupts on the earth's surface to form conical mounds of mud or even lakes of mud if the eruption lasts long enough. These mud volcanoes are usually erupted at lower temperature and with less associated gas and acid than mud volcanoes in active volcanic regions.

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Photograph by S.R. Brantley in September 1983

The mud volcano shown here is from the Norris Geyser Basin, Yellowstone National Park, Wyoming. It is about 40 cm tall.