Mud volcano in Norris Geyser Basin, Yellowstone National Park, Wyoming

Photograph by S.R. Brantley in September 1983

Mud volcano

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.

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

In May, 2006 mud began to erupt from a fissure near the city of Surabaya on the Indonesian island of Java. Because of the large volume of mud that has been extruded, the USGS was invited for a fact-finding visit to assess the ongoing issues in the area. For more information on this mud volcano, please see the Menlo Park Public Lecture Series Talk (video) The Indonesian Mud Crisis Long-lived mud ”eruption“ inundates housing and infrastructure, By Thomas J. Casadevall.