Geothermal features can be observed in areas of active volcanism, or areas that have inactive volcanoes. Subsurface magma heats groundwater, creating steam and hot water. The hot, less dense water rises through fissures and cracks in the ground. When it reaches the surface, features such as geysers, fumaroles, hot springs, and mud pits are created.
Geysers are the most well known geothermal feature. Scientists do not completely understand how geysers work. They think that large amounts of groundwater fill underground cavities. The water in these is heated by nearby magma. Suddenly, some of the water flashes into steam, and the rest is forced violently from the vent in an explosion of hot water and steam. This cycle can be repeated regularly. Old Faithful is a geyser in Yellowstone National Park that has erupted once every 65 minutes for hundreds of years! Fumaroles are also geothermal features that depend on the interactions of released volcanic gases and the local groundwater system.
Geothermal features have great benefits. Geothermal processes create heat and electricity that provide power and hot water to cities in Iceland, New Zealand, Italy and Northern California. As well as being used for energy sources, geothermal waters can also contain minerals and elements such as sulfur, gold, silver, and mercury that can be recovered and used.