SINKHOLE MORPHOLOGY AND DENSITY ON MITCHELL KARST PLATEAU IN SOUTHERN INDIANA

Sinkholes are made on the surface of karst topography where groundwater or rain dissolves limestone creating surface depression. The focus of this project is the examination of sinkholes, their morphology, size, and type to determine their density and relationship with a specific type of bedrock they developed on Mitchell Plateau. We used topographic maps and digital elevation models (DEMs) to trace and measure sinkhole dimensions and density per square kilometer. Mitchell Plateau developed mostly on Blue River Group carbonates (Paoli Limestone, Ste. Genevieve Limestone, St. Louis Limestone) but in its eastern areas it developed on Sanders Group carbonates (Ramp Creek Limestone, Harrodsburg Limestone, Salem Limestone. 7.5-minute topographic maps of Paoli, Crandall, Michell, Corydon East, Laconia. IN, and Fredericksburg were used to measure sinkholes length, width, depth, and sinkhole density per square kilometer. Most of sinkholes on Mitchell Plateau are solution sinkholes and a few are collapse sinkholes. The average sinkhole length is about 31 m (102 ft), the average width is 22 m (72 ft), and average depth is 5 meters (17ft). The highest sinkhole density of 100 per square km was measured in Fredericksburg, IN. 7.5-minute topographic map, and the lowest sinkhole density of 50 per square km was measured in Laconia, IN. We have compared the average depth of ten sinkholes on Mitchell topographic map to same sinkholes on the DEMs, and we have found that DEM measurements indicate slightly deeper sinkholes (7.9 m average) than topographic map measurements (5.8 m average). Our poster will also include data of XRF analysis of rock units that have sinkholes developed on them. We hypothesize that sinkhole density and size are directly related to purity of limestone.