A natural gas field in Derweze, Turkmenistan was identified by Soviet engineers in 1971 as an oil field. When engineers set up a drilling rig, the ground beneath the rig and camp collapsed into a crater (226 ft. crater and 98 ft. deep) and disappeared. To prevent methane gas from escaping, geologists set fire to it expecting it to burn off in a few weeks. The fire has been burning ever since.