Geothermal power generation harnesses the thermal energy from the Earth's magma to create steam that drives the turbine and generator to generate power.
The steam flow used for geothermal power is generated by rainwater seeping underground and being heated by the magma. The amount of heat that magma produces is limitless, and rainfall is infinitely repeated, as a result of one of the Earth's atmospheric phenomena. As such, use of underground steam is a part of infinitely-repeated energy collection cycles, and geothermal therefore is renewable energy.