Geological Survey of Iran photo
Other mud volcanoes arise from the movements of hydrocarbons or other Earth gases. The largest mud volcanoes on land are of this type. They can reach several hundred meters in height, and when the natural gas ignites they can burst out in flames much like a lava volcano. In other places the gas is carbon dioxide and is not flammable; it forms from the metamorphic alteration of deep rocks. This example is from the Makran Range of Iran.