The term mud volcano or mud dome is used to refer to formations created by geo-excreted liquids and gases, although there are several different processes which may cause such activity. Temperatures are much cooler than igneous processes. The largest structures are 10 km in diameter and reach 700 metres in height.About 20% of released gases are methane, with much less carbon dioxide and nitrogen emitted. Ejected materials often are a slurry of fine solids suspended in liquids which may include water (frequently acidic or salty) and hydrocarbon fluids.