Geysers and Hot Springs

Geysers and hot springs are surface expressions of geothermal activity, where groundwater is heated by hot rock or magma not far below the surface. A hot spring forms where this warmed water rises and emerges steadily, sometimes mineral-laden and capable of depositing colourful terraces and crusts around its outlet. Such features are found mainly in volcanic regions and along the edges of tectonic plates, where heat from the interior reaches close to the ground.

A geyser is a rarer and more dramatic type of hot spring that erupts intermittently, throwing a column of hot water and steam into the air. Geysers require a particular combination of conditions: a supply of water, an intense underground heat source, and a system of constricted channels and chambers in the rock. Water collecting deep in this plumbing is heated well above the normal boiling point because the weight of water above raises the pressure. When some of it finally flashes into steam, the expansion forces water out of the vent, which lowers the pressure and triggers a rapid, explosive boiling that empties part of the system before the cycle begins again.

Related geothermal phenomena include fumaroles, vents that release steam and volcanic gases without much liquid water, and mud pots, where acidic fluids break rock down into bubbling clay. Together these features mark areas of high underground heat flow and are studied both for what they reveal about volcanic and hydrothermal systems and for the potential of the same heat to be tapped as geothermal energy. They tend to be concentrated in a small number of geothermal fields around the world.

Frequently asked questions

What makes a geyser erupt?

Water trapped in narrow underground channels is heated under pressure above its normal boiling point. When part of it suddenly turns to steam, the expansion ejects water from the vent, releasing pressure and causing a burst of boiling and eruption.

How is a geyser different from a hot spring?

A hot spring releases heated water steadily, while a geyser erupts intermittently in bursts. Geysers need a special arrangement of constricted underground plumbing that hot springs lack.

What is a fumarole?

A fumarole is a volcanic vent that emits steam and gases with little or no liquid water. Like geysers and hot springs, it indicates strong geothermal activity beneath the surface.