They just overproduced. The first electricity produced by tapping into pockets of steam trapped in the earth made its debut in 1904 in Larderello, Italy. That plant, rebuilt due to World War II damage, is still operating. The first U.S. geothermal plant was a small operation at The Geysers built in 1962. Steam fields are created when water flows through fissures in the rock deep in the earth and is heated by hot magma.
Geothermal plants tap into that pressure and use it to spin turbines.
The plants' cooling towers release plumes of white steam, which can be seen for miles on a clear day. Wet steam plants tap into superheated water in the earth, separate the steam and use it to power generators. The water and the condensed steam is pumped back into the earth.