The Derweze area is rich in natural gas. While drilling in 1971, Soviet geologists tapped into a cavern filled with natural gas. The ground beneath the drilling rig collapsed, leaving a large hole with a diameter of 70 meters (230 ft). To avoid poisonous gas discharge, it was decided the best solution was burn it off. Geologists had hoped the fire would use all the fuel in a matter of days, but the gas is still burning today. Locals have dubbed the cavern “The Door to Hell”.