Why is the air temperature very hot in deep mines?
A combination of: (1) Increasing air pressure — there’s more air over your head (2) The geothermal gradient — the internal temperature of the Earth increases with depth from the surface. Near the surface, the average geothermal gradient is about 25 degrees centigrade (77 degrees Fahrenheit) for every kilometer of depth. Some areas have much higher gradients because of deep fault zones, rifting, magmatic intrusions, or active tectonic forces. The geothermal gradient can make conditions in the super-deep mines uncomfortable, dangerous and deadly. Hot enough to spontaneously explode rocks or bend steel. The TauTona Gold Mine in South Africa is the deepest mine in the world, bottoming out at roughly 3.9 kilometers. Down there natural air temperatures are 55°C (131°F). Without the massive air conditioning, the miners would be unable to work, dropping like flies from heat exhaustion and dehydration. The actual rock face itself can get up to 60 °C (140 °F). The geothermal gradient of 25 deg
