Effects of coal mine subsidence in the Sheridan, Wyoming, area

Analyses of the surface effects of past underground coal mining in the Sheridan, Wyoming, area suggest that underground mining of strippable coal deposits may damage the environment more over long periods of time than would modern surface mining, provided proper restoration pro cedures are followed after surface mining. Subsidence depressions and pits are a continuing hazard to the environ ment and to man's activities in the Sheridan, Wyo., area above abandoned underground mines in weak overburden less than about 60 m thick and where the overburden is less than about 10-15 times the thickness of coal mined. In addi tion, fires commonly start by spontaneous ignition when water and air enter the abandoned mine workings via sub sidence cracks and pits. The fires can then spread to unmined coal as they create more cavities, more subsidence, and more cracks and pits through which air can circulate.