Piping at a geothermal power station. Geothermal power stations generate electricity by harnessing the energy in water and steam that have been heated naturally within the Earth's crust. In areas of volcanic activity this hot water and steam lies at or near the surface. The pipes collect the steam and concentrate it, building up high pressures and speeds (here, 60 metres a second). The steam is then passed through turbines to generate electricity. Photographed at Wairakei Geothermal Power Station on New Zealand's North Island.