How Do Geysers Erupt?

A geyser requires three things: an intense underground heat source (usually magma), a water supply (groundwater), and a specialised plumbing system of narrow, constricted channels. Water seeping deep underground is heated well above 100 degrees Celsius by nearby magma, but the pressure of the water column above prevents it from boiling. When the water at depth finally reaches boiling point despite the pressure, steam bubbles form and expand, pushing water upward. This reduces pressure on the water below, causing more flash-boiling in a runaway chain reaction. The confined plumbing system channels this expanding steam and water vertically, producing the characteristic eruption. Old Faithful in Yellowstone erupts every 44-125 minutes (averaging about 90 minutes), shooting water 32-56 metres high. Geysers are rare: only about 1,000 exist worldwide, with roughly half in Yellowstone. Iceland Strokkur, Kamchatka Valley of Geysers, and Chile El Tatio are other major geyser fields.