Geothermal heat, sometimes called geothermal energy, is the heat energy contained within the Earth. Geothermal heat can be found from a few feet below the earth's crust all the way to its core, about 4,000 miles down. Geothermal heat is stored in solid and molten rock and in underground water.
Facts About Geothermal Heat
Just about anywhere around the world, the temperature a few feet below the Earth's surface is within the range of 45-58 degrees Fahrenheit, no matter the climate. At the Earth's center, temperatures may reach over 9,000 degrees. In comparison, the surface of the sun is approximately 11,000 degrees.
The Source of Geothermal Heat
According to a 2003 article in Science Daily, geophysicists at the University of Berkeley believe they have found evidence that the intense temperatures at the Earth's solid iron inner core are mostly caused by the slow decay of radioactive potassium, uranium and thorium. The outer core -- the area of molten rock, called magma, that surrounds the inner core -- is also extremely hot and can melt the rock surrounding it, called the mantle, so that it, too, becomes magma. Magma occasionally reaches the surface of the Earth through the process known as "convection," where we can see it as lava flowing from an erupting volcano. Although some magma does rise to the Earth's surface, most often it stays within the Earth and heats nearby water and rock, sometimes to a temperature of 700 degrees F. The super-heated water can find its way to the Earth's surface through porous rocks and cracks, creating hot springs and geysers.
Historic Uses of Geothermal Heat
For thousands of years, people fortunate enough to live nearby, such as the Maori of New Zealand, the Romans, Chinese, Japanese and Native Americans, have taken advantage of hot springs, sometimes for relaxation, often for their perceived medicinal properties, as well as for cooking and heating.
The hot springs for which Hot Springs, Arkansas, is named have drawn tourists seeking their curative powers since the early 19th century. Yellowstone National Park in Montana is home to thousands of hot springs and geysers, including the famous Old Faithful.
More Recent Uses of Geothermal Heat
Geothermal heat pumps are a type of furnace-air conditioner combination that, using a looped pipe arrangement, either pump heat from the Earth, just below the surface, to warm the interiors of homes and businesses, or pump heat from these indoor spaces back into the ground.
Geothermally heated underground water has been used in France for six generations for the heating of buildings. Iceland, Poland, Hungary and Turkey also make use of district heating systems. Some communities in the western United States make use of underground geothermal reservoirs to heat several buildings at one time, and the potential exists for hundreds more cities to do the same.
The Future of Geothermal Heat
All that is needed for the generation of electricity is a source of energy that, when directed at the blades of a turbine, turns the turbine fast enough to create an electric field (with the help of a giant magnet) that can be harnessed and sent out to the electric distribution grid for consumer use. Geothermal electric generation involves drilling down into the Earth a mile or more, injecting water into areas of very hot rocks and using the resulting steam to drive turbines above the surface of the Earth, creating electricity.
One advantage of geothermal electric generation is that, unlike coal-, natural gas- and oil-fired power plants, no fuel is required (and, as a bonus, no pollution is created by its burning), and, unlike solar- and wind-powered electric generation, geothermal heat energy is available 24 hours a day, seven days a week. The generation process uses much less electricity because it doesn't have to create the steam to power a turbine, it simply moves it to the Earth's surface.