Rocks beneath the Earths crust contain naturally decaying radioactive materials like uranium, producing a continuous supply of heat. The amount of heat within 10,000 metres of the Earths surface contains 50,000 times more energy than all the oil and gas resources in the world.
Geothermal energy is power generated by the harnessing of heat beneath the Earths surface. Wells are used to pipe steam and hot water from deep within the Earth, up to the surface. The hot water is then used to drive turbines and generate electricity. The regions with highest underground temperatures are in areas with active or geologically young volcanoes. These "hot spots" often occur around the Pacific Rim. This area is also known as the "Ring of Fire" due to the large number of volcanoes.
In the UK at a depth of about 1500 to 3000 metres below the surface there are some aquifers that contain water at very high temperatures. This water can be pumped up to the surface and used in heating schemes.