Photograph by S.R. Brantley in September 1983 Castle Geyser erupts water and steam, Yellowstone National Park, Wyoming.

Geyser Most geysers are hot springs that episodically erupt fountains of scalding water and steam. Such eruptions occur as a consequence of groundwater being heated to its boiling temperature in a confined space (for example, a fracture or conduit). A slight decrease in pressure or an increase in temperature will cause some of the water to boil. The resulting steam forces overlying water up through the conduit and onto the ground. This loss of water further reduces pressure within the conduit system, and most of the remaining water suddenly converts to steam and erupts at the surface.

Did you know?

• Geyser is an Icelandic word meaning "to gush or rush forth."
• The world's premier geyser fields are in Iceland, New Zealand, and Yellowstone National Park, Wyoming.
• Some geysers erupt from cold or warm springs and are powered by gas pressure instead of the actual boiling of water.
• Most of the world's geysers are near regions of volcanic activity, which supply the heat needed to boil shallow ground water.