Geysers are hot springs that episodically erupt columns of water. They occur in few places on Earth. The highest concentration of geysers anywhere is at the Yellowstone Hotspot Volcano (northwestern Wyoming, USA).

Fountain Geyser is a large, regularly-erupting feature in the Fountain Group of Yellowstone’s Lower Geyser Basin. It has a moderately large, irregularly polygonal surface vent that is 6 to 12 meters across. The vent is surrounded by a geyserite platform with moderately developed concentric ridges at its eastern edge. Eruption starts are preceded by a relatively rapid rise in water level. Eruptions occur every ~4.5 to 6 hours and last for about 30 minutes. Some eruptive bursts reach up to ~80 feet high. Much of the erupted water volume moves northward into Morning Geyser’s basin, which overflows and then heads north into a large field of weathered geyserite gravel. Bursting patterns show that Fountain Geyser erupts from two major subaqueous vents.