A geyser is a natural pressure cooker, and Iceland once coaxed one awake with soap
Geysers need heat from nearby magma, a water supply and underground plumbing with just the right narrow throat. The cooler water on top acts like a pressure-cooker lid until the hot water below flashes into steam. So fragile is the balance that Iceland's original Geysir was sometimes kicked into eruption with soap.
The English word dates to the late 18th century and comes from Geysir, a particular Icelandic spring whose name means gusher. Surface water seeps down, on average to about 2,000 metres, where it meets rock heated by magma. In an ordinary hot spring the warmed water simply rises back by convection. A geyser differs because constrictions in its channels trap the water, so the reservoir becomes superheated, liquid well above its normal boiling point.
Eventually boiling starts at the bottom and bubbles push some water out of the vent. That lightens the column, the pressure drops, and the superheated water flashes to steam all at once, blasting a froth of steam and water skyward. Then the reservoir refills and the cycle restarts. Rhythms vary widely: Iceland's Strokkur bursts briefly several times an hour, whereas Grand Geyser in Yellowstone plays for up to 10 minutes every 8 to 12 hours.
Geysers are rare and easily ruined. Loose rock erodes the channels; mineral deposits clog them; earthquakes rearrange them. People have killed geysers by throwing debris into them, and geothermal power plants have drained others. New Zealand's Taupō zone lost most of its geysers to development and a hydroelectric reservoir. The same zone once held Waimangu, the largest geyser ever known, which erupted from 1900 for four years, typically to 160 metres, before a landslide shifted the water table.
Yellowstone holds roughly 300 to 500 geysers, about half the world's total, including Steamboat, the tallest active geyser. Russia's Valley of Geysers in Kamchatka ranks second, with about 200. Their scalding water is not lifeless: heat-loving microbes thrive there, and Thermus aquaticus, the first found and most important for biotechnology, supplies heat-stable enzymes. On Saturn's moon Enceladus and Neptune's moon Triton, jets called cryogeysers spray vapour into space.
Source: Geyser
