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We recently received a question about how mud volcanoes form and why they're distinct from "real" volcanoes (the kind involving magma), so we're here to give you the dirt on the difference. 

Steam rises from a circular crater in the center of a watery lake of mud. Mud berms surround the hole, with dead, drowned trees reaching bare branches skyward. In the distance, villages of red-tiled houses are visible.

Many mud features are associated with fault boundaries - subduction, lateral faults, and any other place that a break in the crust makes it easy for liquid and gas to travel to the surface. Mud volcanoes, however, are places where sediments suspended in fluids are pressurized by tectonic activity or the accumulation of hydrocarbon gases. The pressure forces the mud upward, where it erupts on the surface of the earth and (occasionally) just offshore in underwater environments. Most of these 'volcanoes' are small - only a few cm to a few m high - but those that erupt massive amounts of mud over long periods of time can be km in diameter and dozens of meters high.

The largest mud volcanoes actually do pose hazards, but not of the usual volcanic kind. Instead, the sheer volume of mud erupted can flood the landscape, displace people, and bury infrastructure and agriculture. One mud volcano in East Java, Indonesia (…) has displaced more than 40,000 people, destroyed villages, and caused billions of dollars in damage. Because they're associated with hydrocarbon reservoirs, mud volcanoes are also a source of greenhouse gases, particularly methane and carbon dioxide.

Small explosion of dark gray mud rises from a steaming patch of muddy ground. Around the mud pot are other patches of steam.

Does California have mud volcanoes? Not quite. California's mud seeps (or mud pots) appear only in active geothermal areas, including Bumpass Hell and the Devil's Kitchen at Lassen, the Davis-Schrimpf Seep Field near Salton Buttes, and places in The Geysers geothermal field south of Clear Lake. The mud that 'erupts' from these features is hot, and created by water, steam, and gases which are related to a deeper volcanic system. In contrast, true mud volcanoes are cooler, and can form without magmatic heat or fluids being involved. The confusion likely comes from the fact that both mud pots and mud volcanoes can build cone- or dome-shaped edifices on the surface. Same shape, different origin!

Check out this Volcano Watch article for more mud volcano facts!…

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