|geothermal (jē'ō-thûr'məl) Pronunciation Key
Relating to the internal heat of the Earth. The water of hot springs and geysers is heated by geothermal sources. ◇ Geothermal energy is power generated from natural steam, hot water, hot rocks, or lava in the Earth's crust. In general, geothermal power is produced by pumping water into cracks in the Earth's crust and then conveying the heated water or steam back to the surface so that its heat can be extracted through a heat exchanger, or its pressure can be used to drive turbines.