Geothermal energy is formed within the Earth. Geothermal energy is clean and stable, but it's only available near tectonic plate boundaries. Plate boundaries are where volcanic activity and earthquakes occur.
The U.S. Energy Information Administration mentions that the word "geothermal" comes from the Greek words geo, meaning earth, and therme, meaning heat. Ancient cultures, including the Romans, Native Americans and Chinese, used geothermal heat for heating, cooking and bathing. In modern times, many believe the water from natural hot springs contains rich minerals that heal the body. People have enjoyed geothermal heat in hot springs for thousands of years. In certain parts of Iceland, hot water from geothermal plants runs under roads and sidewalks to melt ice.
Power plants tap into geothermal energy by using steam or hot water reservoirs to generate electricity. A standard geothermal system uses pipes buried more than 4 feet beneath the ground. A liquid is pumped into the pipes to absorb and transmit the heat. People use wells to pump steam or heated water to the surface for home use, and geothermal output is used as a heating and cooling source for buildings.
Geothermal plants are common in the western part of the United States due to the abundance of hot water reservoirs. Because of the slow decay of radioactive particles, the Earth's core generates heat that is hotter than the surface of the Sun.