geisir

Geisir is the Icelandic term for the natural geothermal eruption feature known in English as a geyser. A geisir is a spring or vent in a geothermal area that periodically ejects jets of hot water and steam into the air. The eruptions arise when groundwater is heated by underlying magma, becomes pressurized as it near its boiling point, and finally erupts through a surface opening, often accompanied by a plume of steam.

Geisir are classified mainly by their eruption style. Fountain geysers eject jets from many points around a pool, producing a bubbly, irregular jet. Cone geysers eject water through a narrow vent bounded by mineral deposits, often forming a visible cone around the opening. Eruption intervals, duration, and water temperature vary with underground conditions, including heat flow, water supply, and rock permeability.

Geisir are most common in tectonically active regions with abundant subsurface heat. Notable concentrations occur in Iceland, the western United States (notably Yellowstone), and parts of New Zealand. The term geyser itself originates from the Icelandic geisir, with Geysir in Haukadalur giving the name to geysers worldwide. Other well-known examples include Strokkur in Iceland, which erupts regularly, and Old Faithful in Yellowstone, renowned for its predictability.

Safety and visitor access are important considerations in geisir areas. Eruptions can be dangerous due to scalding water and gaseous emissions, and many sites restrict proximity and off-trail activity to protect both visitors and fragile geothermal features. Geisir also attract scientific study and geothermal energy interest, contributing to our understanding of subsurface heat and hydrothermal systems.