The greater the pressure, the higher the boiling point. The hot water flashes to steam when the pressure is released as it reaches the surface. This phenomenon also occurs naturally, resulting in such features as geysers. CO 2 also occurs naturally in large amounts in molten magma, which is involved in the explosive eruption of volcanoes. See Greenhouse Effect.
Examples are coal and oil, which have energy potential that is released upon combustion.
Water-cooled geothermal power plants use cooling towers to cool the used steam and condense it back to water for injection back to the edge of the reservoir. The heat from geothermal water, for instance can be conducted through metal plates or pipes to heat other water for district heating systems or a second organic liquid for use in binary power plants. See Plate Tectonics. These motions are thought to be party of the dynamic geologic processes that drive the movement of crustal plates. Earth's crust insulates us from the hot interior.