The word geothermal literally means “earth heat” (geo is Greek for earth; therme means heat). Geothermal zones are areas of high heat within the earth’s crust. The crust is the outermost layer, ranging between 35 and 70 km thick in most regions. The mantle, with layers of intensely heated rock, lies directly under the crust. Located deep under the earth or closer to the surface, the depths where geothermal heat can be found—and tapped— depend on the thickness of earth’s crust. In countries along the East African Rift Valley like Uganda, Kenya and Tanzania, and in Pacific Rim countries like New Zealand, the Philippines and Indonesia, the crust is relatively thin or fractured, containing deep cracks and fault lines. In such regions the geothermal heat, rooted in the underlying mantle, lies closest to the earth’s surface.  The geotherma gradient, which is the increase in subsurface temperatures with increasing depth underground, is high. Water seeps down through the cracks and its temperatures shoot high as it makes contact with hot subterranean rocks.

“Wherever you have high volcanic activity…you will very likely have geothermal energy available close to surface,” explains Stephan Singer, the director of global energy policy with the World Wide Fund for Nature (WWF).

Modern geothermal technology has found ways of tapping the steam and converting it into usable energy. Drilling the earth at an appropriate site will give rise to boiling water and steam. The blend surges up like a bold signature of the earth’s own creation in eons past. Seated in the vast subterranean expanses, geothermal resources are considered to be renewable. The geological backdrop of geothermal energy goes all the way back to the  earth’s creation.