About A Geothermal Reservoir
The first thing you need to know is that the heat from Earth's core flows outward continuously. Sometimes, the heat-in the form of magma reaches the surface as lava, but it stays underneath the Earth's crust. The magma heats nearby water and rock to levels as hot as 700*F. When water is heated by the Earth, the superheated water, or maybe steam, is trapped under a layer of porous rocks. This is altogether "enveloped" by a layer of watertight rock. The result is a geothermal reservoir!! Rainwater can also trickle down into the natural reservoir and add a bit more water. Geothermal power plants use the superheated water inside the reservoir to produce electricity.