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Natural Displays of Geothermal Energy

Volcanoes, fumaroles, boric-acid fumaroles and geysers: when nature puts on a show.

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The heat of the Earth used to produce geothermal energy stems from impressive and spectacular natural phenomena that are intrinsic to our planet. The best-known natural displays of geothermal energy are volcanoes, fumaroles, boric-acid fumaroles and geysers.


Volcanoes are the most famous natural display of geothermal energy on the planet. Extremely complex geological structures, they have been generated within the earth’s crust since the beginning of time by the rising – following eruptive activity – of molten rock mass, magma, formed below or inside the earth’s crust. The temperature of magma outflow is usually between 650 and 1200°C.

About 91% of Earth’s volcanoes are underwater, while there are about 1500 that are active on land. The land around volcanoes has great geothermal potential, which can be used to produce renewable energy, like at the Cerro Pabellón plant in Chile.

1. Cerro Pabellón (Cile) | 2. Fumaroles | 3. Gayser


Fumaroles are secondary volcanic phenomena. These small but deep cracks in the ground release gas at temperatures that can range from 100 to 900°C. The drop in temperature when the gas comes in contact with the air causes it to condense and creates fumes, which is where the phenomenon gets its name.

Fumaroles are generally located near craters or active volcanoes, as well as in areas where volcanic activity has stopped, but minor geothermal, or even hydrothermal, events still happen. Their complex chemical composition features a very strong acidity (with a pH almost at zero) and profoundly alters the surrounding soil, where the yellow coloring of sulfur often stands out.

Boric-acid Fumaroles and Geysers

Boric-acid fumaroles are violent emissions of water vapor from the subsoil, at temperatures between 150 and 230°C.  They feature constant emissions and very high pressure (up to 20 atmospheres). Boric-acid fumaroles are the main feature of the Larderello area.

Geysers are very rare sources of boiling water, as they require geological and climate conditions that are found in very few areas of the planet. Iceland and Yellowstone National Park (in Wyoming, USA) are the two most famous areas featuring geysers: in both, a large quantity of geothermal energy is produced.

Geysers are powerful jets of water and steam, usually erupting at regular intervals. The duration of the jet can vary from a few seconds to several minutes. The name comes from the Icelandic verb gjósa, meaning to erupt, or to release in jets. And Geysir is the name of the most famous Icelandic geyser, which, in its most active periods, was able to emit jets up to 60 meters high.

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