A natural and renewable source of thermal energy extracted from regions of volcanic activity such as fumaroles, hot springs, and geysers. The heat is extracted by drilling a borehole down into the high-temperature porous rock, which ranges from just below the surface of the Earth in some places, to several kilometres down. Hot water and steam is either brought to the surface and used directly, or water is sent down where it is heated by conduction and returned to the surface. Geothermal energy is used for domestic or district heating, industrial processes, or for power generation in turbogenerators. Countries that use significant amounts of geothermal energy include the US, the Philippines, Iceland, and New Zealand. The district heating system in Reykjavik, Iceland provides heat for 95 per cent of the buildings.