geyser

Castle Geyser erupts water and steam, Yellowstone National Park, Wyoming. Credit: S.R. Brantley / U.S. Geological Survey

A hot spring, found in currently or recently volcanic regions, that intermittently jets superheated water and steam into the air. A geyser consists essentially of a tube leading down to a hot source. Groundwater accumulates in the tube, that near the bottom being kept from boiling by pressure of the cooler layers above. When the critical temperature is reached, bubbles rise, heating the upper layers which expand and well out of the orifice. This reduces the pressure enough for substantial steam formation below, with subsequent eruption. The famous Old Faithful used to erupt every 66½ minutes, but has recently become less reliable.

More facts about geysers

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.

Related category

• GEOLOGY AND PLANETARY SCIENCE

Source: U.S. Geological Survey

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