Energy

What it is

Heat is thermal energy. Consequently, the heat contained inside the Earth is called geothermal energy. However, the term geothermal energy is used to define the fraction of the earth’s heat which can be exploited by human beings. The earth’s inner structure is similar to that of an egg. The yoke is the central core, the albumen represents the mantle, the shell is the earth’s crust. The top layer of the mantello, upon which the crust rests, is made of a fluid called magma. When the magma finds a way out towards the surface, it creates volcanoes and is termed lava.

Geothermal gradient
By moving from the surface towards the core of the earth, the temperature rises by approximately 2/3°C each 100 metres. That increase is called “geothermal gradient” and is not constant. There are areas where it amounts to less than 1°C per 100 metres, whereas in other “hot” or “geothermal areas” it can be 10 times higher. They include volcanic areas where magma is a more shallow depth, so that the temperature exceeds 300°C at 500/1000 metres.