(Icelandic geysir, “to rush forth”) Any hot spring that discharges jets of steam and water intermittently, generally associated with recent volcanic activity and produced by the heating of underground waters that have come into contact with, or are very close to, magma. Geyser discharges as high as 1,600 ft (500 m) have been recorded, but 160 ft (50 m) is much more common (e.g., Old Faithful in Yellowstone National Park). Occasionally, a geyser will adopt an extremely regular and predictable pattern of intermittent activity and discharge for a few minutes every hour or so.

This entry comes from Encyclopædia Britannica Concise.
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