Have you ever marveled at the power and predictability of Yellowstone's Old Faithful Geyser? Enjoyed a dip in a hot spring? Turned on any electric appliance in Reykjavik, Iceland? If so, you have already been introduced to geothermics.
"Geothermics" is the energy that is being released from the interior of the Earth in the form of heat. The process is not well-understood even today; it is estimated that between 45 and 90% of this heat is a product of radioactive decay from such elements as uranium, potassium, and thorium in the planet's mantle. Other possible sources include heat from the tidal forces of Earth's rotation (the crust compresses and distorts as the Earth spins, causing friction); heat from the friction of sinking heavy metals such as iron, nickel, and copper as they fall toward the Earth's core (these elements are both original components of the Earth's crust and products of metallic meteors); and heat generated by the Earth's magnetic field.
As a result the interior of our planet is incredibly hot, and the temperature rises with increasing depth. Just 50 or 60 miles below the surface, the temperature reaches an estimated 1200 to 2200 degrees Fahrenheit (650 to 1200 degrees Celsius). The core may be more than 12,000 degrees F (6735 C), but nobody knows for sure. Around the globe, internal heat leaks out at a constant background rate as the planet cools, mostly via diffusion and the slow convective boil of the mantle, the liquid layer upon which the crust rides. At certain places where the Earth's crust is thinner than average and magma from the mantle is close to the surface, the heat seeps out at a higher rate. These sites include coastal volcanoes, geological "hotspots" such as those underlying Yellowstone and the Hawaiian Islands, and spreading zones where the crust is being pulled apart, such as Iceland, the mid-Atlantic ridge, and Africa's Rift Valley.
People have used the phenomenon of geothermal heating for centuries, if not millennia. Japanese, Koreans, and the Norse settlers on Iceland piped water from hot springs into their houses as early as the 14th century to provide a source of central heating. The fierce Maori people of New Zealand used hot pools for cooking game, roots... and conquered human enemies.
Today, those nations around the world that are so lucky as to have abundant geothermal activity are using the Earth's own power to generate electricity. Nuclear, coal, and gas-powered power plants use the energy from those processes to turn water into steam, which then drives turbines, creating electricity. Geothermal plants often simply use steam produced naturally by the Earth itself to turn the turbines. In other places, water is piped down into hot dry areas of the crust, where it flashes into steam, once again turning the turbines that light cities.
New Zealand is one of the world's foremost producers of geothermal energy; 12% of the country's electricity comes from geothermal sources. Other producers span the globe: in fact, a number of cities run almost entirely of geothermal energy, including Reykjavik, Iceland; Budapest, Hungary; Klamath Falls, Oregon; and Boise, Idaho. The Italian province of Tuscany has been using geothermal energy since 1904.
Geothermal power is a boon to the environment since, unlike fossil fuel-powered plants, it does not release carbon dioxide or poisons such as mercury into the air. The only major disadvantage of geothermal electricity production is that the process of extracting steam from the Earth's crust can disrupt nearby geysers, hot springs, and fumaroles. Nonetheless, geothermics can provide clean, renewable energy that will be freely available for billions of years into the future... until the Earth itself runs out of steam.
Sources:
Environment Waikato Regional Council, "Energy and Extraction" (Feb 26, 2007).
http://www.ew.govt.nz/enviroinfo/geothermal/energy.htm
Wikipedia, "Geothermal (geology)" (accessed Feb. 25, 2008).
http://en.wikipedia.org/wiki/Geothermal_%28geology%29
MSN Encarta, "Geothermics" (accessed Feb. 25, 2008).
http://encarta.msn.com/encyclopedia_761562283/geothermics.html
