What is Geothermal?
The word geothermal  comes from the Greek words "geo," meaning earth and "therme," meaning heat.  Geothermal heat is generated from within the earth's core, some 4,000 miles below the surface.  The heat is produced mainly by the slow decay of radioactive materials such as uranium and potassium found in the various materials that make up the earth's interior.  The amount of heat within 10,000 meters (about 33,000 feet) of Earth's surface contains 50,000 times more energy than all the oil and natural gas resources in the world. 

The earth's interior is made up of different layers including, the core, outer core, mantle and the crust.  The core is made of iron, the outer core is melted rock, called magma.  The mantle, which is approximately 1,800 miles thick, surrounds the core and outer core and is made up of magma and rock.  And, finally the crust, which is the very thin layer, that forms the continents and ocean floors.  This outermost layer is anywhere between 3-35 miles thick - shallower under the ocean floor then the continents.  And, as we all know this crust is not uniform, it is comprised of large, distinct pieces called plates.  These plates interact at their boundaries in three ways:  by sliding or grinding past each other (transform boundaries), by colliding (convergent) or pulling apart (divergent or spreading).   The latter two interactions tend to bring magma to the surface, or at least closer to the surface making the heat more accessible. 

This heat can be used as an energy source in many ways, from large and complex power stations to small and relatively simple pumping systems.  This heat energy, known as geothermal energy, can be found almost anywhere, so it is far more common than you might think.  Some applications of geothermal energy use the earth's temperatures near the surface, while others require drilling miles into the earth. The three main uses of geothermal energy are:  
  • Direct Use and District Heating Systems which use hot water from springs or reservoirs near the surface.
  • Electricity generation in a power plant requires water or steam at very high temperature (300 to 700 degrees Fahrenheit). Geothermal power plants are generally built where geothermal reservoirs are located within a mile or two of the surface.
  • Geothermal heat pumps use stable ground or water temperatures near the earth's surface to control building temperatures above ground.

Tapping geothermal energy is an affordable and sustainable solution to reducing our dependence on fossil fuels, and the global warming and public health risks that result from their use.