Geothermal Energy:
The temperature increases as one goes inside the earth and the temperature at Earth’s center is about 6000°C. If the crust is thin, the temperature can even be 250°C a few kilometers down. Temperature increases by about 3°C for every 100m increase in depth. So, it is very obvious that one will find heated rock hot enough to boil water at some distance below the ground. Geothermal energy is the energy obtained from the stored heat inside the earth’s crust. This form of energy was prevalent since the existence of the earth.
The crust floats over the molten mantle known as magma. When magma gushes and forces out through the cracks and faults in the earth’s surface during a volcanic eruption, it is called lava. If water comes close to or in contact with such hot rocks it starts boiling and quickly changes into steam. The temperature may be more than 300°F and when this hot water comes out through cracks, it is called a hot spring, such as Emerald Pool at Yellowstone National Park. Sometimes the hot water explodes in the air to form a geyser like Old Faithful Geyser. When holes are drilled, the steam comes up which can then turn turbines to drive electrical generators.