geothermal energy

Geothermal energy is derived from the natural heat present below the surface of the Earth. Cool water is pumped down where it is heated up in large underground reservoirs before being pumped back to the surface.

Geothermal activity at Rotorua in the Bay of Plenty area of New Zealand's North Island. Rotorua is in a volcanic zone, which produces hot thermal springs, geysers, and pools of boiling mud. Among the vapour is hydrogen sulphide gas, which smells like rotten eggs.

Wairakei geothermal power station, New Zealand.

The Blue Lagoon, near Keflavik, is one of Iceland's most popular tourist destinations. It is not a natural geothermal spring; it is a pale blue pool of hot water emitted from the Svastgensi geothermal power plant. Algae thrive in the hot saline water, but as the water cools in the air they die. The silica-rich mud on the floor of the lagoon, and the dead algae in the water, combine to give the lagoon its colour.

Nesjavellir geothermal power station, Thingvellir, Iceland. Geothermal energy is a form of renewable energy that uses the natural heat of the Earth to heat water. The hot water or steam can then be converted into electricity. Nesjavellir is situated in an area of volcanic activity and has higher than normal rock temperatures near to the surface.

Energy extracted for heating and electricity generation from natural steam, hot water, or hot dry rocks in the Earth's crust. It is a form of renewable energy. Water is pumped down through an injection well where it passes through joints in the hot rocks. It rises to the surface through a recovery well and may be converted to steam or run through a heat exchanger. Steam may be directed through turbines to produce electrical energy. It is an important source of energy in volcanically-active areas such as Iceland and New Zealand. The Earth's internal heat is produced by the decay of radioactive substances in the rocks.