geyser

A geyser is a spring or vent in which groundwater is intermittently heated by geothermal energy and erupts as jets of hot water and steam. Geysers occur where hot rocks near magma heat subsurface water, which becomes pressurized as it flows through narrow channels. When the water rises to shallower depths and pressure drops, it flashes to steam, expands rapidly, and powers an eruption that ejects a column of water and steam.

Formation and behavior vary with geology. Geysers require a heat source, an adequate water supply, and a constricted plumbing system that traps steam and water. Eruptions are influenced by water chemistry, mineral deposits, and the recharge rate of the underground reservoir. Most active geysers are found in volcanic regions, such as Yellowstone in the United States, Iceland, and parts of New Zealand.

Types and patterns include cone geysers, which eject from a narrow vent with mineral-deposit-tipped rims, producing tall, relatively predictable eruptions; and fountain geysers, which erupt from wider openings and can be more irregular. Eruption intervals range from minutes to days and can last from a few seconds to several minutes.

Notable examples include Old Faithful in Yellowstone, famous for its roughly regular intervals; Strokkur in Iceland, which erupts every several minutes; and the historic Great Geysir in Iceland, once highly active. Geysers are sensitive to environmental changes; groundwater withdrawal, climate effects, or tourist disturbance can alter their activity or threaten their preservation.

The term geyser derives from the Icelandic geiser (geisir), named after the Great Geysir.