As we move deeper from the surface of the earth to the core, we see an increase in temperature, called the geothermal gradient. Near the surface of the earth, the geothermal gradient has an average value of about 30 ° C per km depth. In some areas, either due to recent volcanic volcanoes or hot water rise from deep depths through cracks, the geothermal gradient is significantly above 30 ° C, resulting in relatively low depths of aquifers containing high water or steam. temperature. These areas are called geothermal fields and in these areas the exploitation of geothermal energy is extremely advantageous. When hot water or steam finds a way out through some opening of the Earth's crust to its surface then we have hot springs or hot springs.