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

FRONTISPIECE.-Aerialobh'que views showing surface sub sidence effects above abandoned coal mines 10-15 km north of .Sheridan, Wyo.A, Aerial obh'que view of sub sidence depressions and pits above the Old Monarch mine in operation from 1904from to 1921from (May 1978)).Rectangular depressions, some of which are bounded by pits or locally include pits, are evident at right.Some of the pits are sealed at the bottom and provide sufficient moisture to support trees (foreground).Overburden thickness is estimated to be approximately 10-15 m.The depressions occur where much of the coal is removed and the remaining coal cannot support the weight of the overburden.Pits at the margins of the depressions commonly are caused by piping failure and the local flow of surface water to CONTENTS ------------Page --------------------"--------------•----"""--•"-"---•-••---"-"-""•"-j. -------•--------»-"---------------"----------""•-"-•"••"-""--""•"""