A mud volcano is an accumulation of mud and water extruded at the surface of a planetary body by volcanic gases. Mud volcanoes are typical features of hydrothermal activity in volcanic areas and often associated with other gaseous manifestations such as fumaroles and geysers. Gases associated with mud volcanoes are predominantly methane, followed by carbon dioxide and nitrogen. Around mud volcanoes, communities of thermophilic prokaryotes and biofilms develop. Pitted cones, mounds, and flows occurring at the surface of Mars may have formed through processes akin to terrestrial mud volcanism. However, on Mars, the main processes are probably sedimentary, with release of gas from sedimentary strata via gravity destabilization.