Geysir (gā`sĭr), hot spring, SW Iceland, c.75 mi (120 km) W of Reykjavík. Although in medieval times it erupted three times daily, weeks now elapse between eruptions. The height and temperature of the jet are variable, reaching up to 200 ft (60 m) and 180°F; (82°C;). There are many other hot springs in the vicinity, but few have eruptions. Hot water is piped into Reykjavík and used for heating. The generic term geyser in English is derived from Geysir.