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Geothermal Steam and Mud

The famous Pohutu Geyser is a highlight for many tourists visiting Rotorua. Image: GNS Science.

The famous Pohutu Geyser is a highlight for many tourists visiting Rotorua. Image: GNS Science.

When rainwater percolates into the ground in a geothermal area, it is heated and eventually rises back to the surface to create the many features we associate with geothermal - geysers, boiling mud, hot springs and fumeroles. Taupo and Rotorua are famous for these geothermal features.

Visit the Earth Energy Learning Zone for more information about geothermal energy.

Geysers: Geysers are caused when water seeps down from the surface onto concentrations of hot rock, heats up rapidly and then explodes out of the nearest available vent. It is just like a pressure cooker down there in the geysers plumbing system.

Hot springs: Springs are produced by the emergence of geothermally heated groundwater from the Earth's crust. Their colour is determined by the temperature, chemistry and microbiology of each pool.

Fumaroles: A fumarole is a hole in the earth that emits steam and gases, such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. They can occur along tiny cracks or long fissures, and individually or in clusters.

Monitoring a fumarole at White Island. Image: Julian Thomson.

Monitoring a fumarole at White Island. Image: Julian Thomson.

Mud pools: Pools of bubbling mud form in high-temperature geothermal areas where water is in short supply.

Silica terraces: Geothermally heated water contains large amounts of dissolved silica. When these waters reach the surface they cool rapidly and precipitate solid silica, which create terraces and other features at the surface. In 2011, a team of scientists led by Cornel de Ronde of GNS Science, rediscovered the famous Pink and White Terraces, 125 years after they were drowned in Lake Rotomahana, following the brief but devastating eruption of Mount Tarawera on June 10th 1886.