The solid outermost layer of the Earth, mostly consisting of rock, and ranging from 3 - 35 miles (4.8 - 56 kilometers) thick, comprises the topmost portion of the lithosphere. Earth's crust insulates us from the hot interior.

Energy Resource

A source of useable power, which can be drawn on when needed. Energy resources are often classified as renewable or non-renewable.


The ability to do work, such as making things move and heating them up. Energy can take many forms, including electrical, chemical, radiant, mechanical and heat.


A small hole or vent in the Earth's surface, found near volcanic areas, from which steam or gases shoot out.


A machine that converts mechanical power into electricity by spinning copper wires (conductors) within a magnetic field.

Geothermal Energy

The word "geothermal" literally means "Earth" plus "heat." Energy that is generated by converting hot water or steam from deep beneath the Earth's surface into electricity.

Geothermal Reservoir

A large volume of underground hot water and steam in porous and fractured hot rock. The hot water in geothermal reservoirs occupies only 2% to 5% of the volume of rock, but if the reservoir is large enough and hot enough, it can be a powerful source of energy. Geothermal reservoirs are sometimes covered by a layer of impermeable rock. While geothermal reservoirs usually have surface manifestations such as hot springs or fumaroles, some do not.

Geothermal Power Plant

A facility which uses naturally occurring steam or heat to drive turbine-generators to produce electricity. Three different types make use of the various temperature ranges of geothermal resources: dry steam, flash and binary.

Geothermal Resource

The natural heat, hot water and steam within the Earth.

Geothermal Water

Water heated by the natural heat inside the Earth.


A natural hot spring that sends up a fountain of water and steam into the air; some geysers "spout" at regular intervals and some are unpredictable.

Hot Springs

A natural spring of water this is warmer than body temperature and therefore feels hot; may collect in pools or flow into streams and lakes. A geothermal phenomenon.

Injection Well

A well through which water is injected into an underground reservoir. Geothermal production and injection wells are constructed of pipes layered inside one another and cemented into the earth and to each other. This protects any shallow drinking water aquifers from mixing with deeper geothermal water.


Hot, thick, molten (liquid) rock found beneath the Earth's surface; formed mainly in the mantle.

Power Plant

A central station where electricity is produced using turbines and generators.


The force exerted over a certain area. Our atmosphere exerts pressure on the surface of the earth, and layers of rock exert pressure on those below them.

Renewable Resource

A resource that can be used continuously without being completely depleted (because it regenerates itself within a useful amount of time). Examples include water (small hydro) and wind power, solar energy and geothermal energy.


The vapor form of water that develops when water boils. Steam is made of very tiny heated water particles (molecules), which are bouncing around and bumping into each other at very high speeds. These heated water molecules are also spreading out and expanding in every direction they can. If we confine or trap water in a container, with a pipe as an opening, and heat the water to steam, it will create great pressure in the container and will rush out the pipe with a great deal of force. This force (the "power" of steam) can be put to work turning a turbine connected to an electricity generator.


A machine with blades that are rotated by the forceful movement of liquid or gas, such as air, steam or water or a combination.