Coal Mine Subsidence Near Sheridan, Wyoming

Abstract

Studies of coal mine subsidence features in a 30-sq. mi area 3–12 mi north of Sheridan, Wyo., indicate that the long-range surface effects of mining thick coal beds underground beneath weak overburden less than about 200 ft thick are greater than the effects of well-planned surface mining practices with proper reclamation and revegetation. Coal resource recovery also is higher and more efficient in most surface mining operations. Subsidence depressions, cracks, pits, and troughs above underground mine workings can render the surface unusable for development because of the hazard to people and structures. Surface drainage and ground water can be disrupted or diverted by depressions, cracks, and pits above underlying coal mines, which, in turn, can dewater root systems of vegetation and affect water rights. Fires may start by spontaneous ignition in abandoned coal mines if air and water under the right conditions reach surface mine highwalls or underground workings through subsidence cracks, pits, or troughs. Fires in underground mines commonly are a greater hazard to people, animals, and structures than fires in surface mine highwalls because: (1) a greater volume of fuel commonly is available in underground mines, (2) the underground fires may not be apparent on the surface until they are very extensive, and (3) fires on highwalls can be controlled much more easily than underground fires.