Hot springs can be geysers, where jets of water shoot out of the ground; fumaroles, where steam seeps from the ground; mud pots, in which water and mud or clay bubbles in holes on the surface; or hot water spilling from the ground.
Hot spring water is heated underground by hot rocks or magma. The latter is responsible for geysers and is usually found over geologic "hot spots," where magma is closer to the surface.
Locations in the U.S.
Some notable hot spring locations are Olympic Hot Springs in Washington, Palm Springs in California and Yellowstone National Park in Wyoming.
Hot springs--and especially geysers--can be dangerous as some reach the surface at temperatures above boiling.
Probably the most famous hot spring in the United States is the geyser "Old Faithful" at Yellowstone National Park. It shoots a jet of water at an average height of 145 feet.