SINKHOLE MORPHOLOGY AND DENSITY ON MITCHELL KARST PLATEAU IN SOUTHERN INDIANA

Sinkholes are made on the surface of karst topography where groundwater or rainwater dissolves limestone creating surface depressions. Most sinkholes on Mitchell Plateau are solution sinkholes and a few are collapse sinkholes. The focus of this project is to examine the morphology of sinkholes to determine their relationship with specific units of limestone on the Mitchell Plateau. Our hypothesis is that sinkhole density and size are directly correlated with the purity of limestone. Blue River Group carbonates are more pure and higher in CaCO₃ content, where we expect to find higher density of sinkholes than in Sanders Group carbonates, which contain more silica (SiO₂) and dolomite (MgCa(CO)₃). We used 1-meter resolution digital elevation models (DEMs), and ArcGIS Pro to map and measure sinkhole dimensions and density per square kilometer. XRF analysis was used to analyze the composition of the limestone to find the highest concentration of calcium carbonate. Dimensional data from the 7.5-minute topographic maps of Paoli, Crandall, Mitchell, Corydon East, Laconia, Bedford, and Fredericksburg, IN. were compared to the ArcGIS data. The Mitchell Plateau developed mostly on Blue River Group carbonates (St. Louis, Ste. Genevieve, and Paoli limestones) but in its eastern areas it developed on the Sanders Group carbonates (Ramp Creek, Harrodsburg, and Salem limestones). The average sinkhole length is about 87 m (285 ft), the average width is 62 m (203 ft), and average depth is 4 meters (14ft). The highest sinkhole density, measured at 108 per square kilometer, was found in northern Fredericksburg, IN. Conversely, the lowest sinkhole density, at 32 per square kilometer, was recorded in the southern Mitchell, IN quadrangle, both areas mapped on a 7.5-minute topographic map where the Blue River Group is located. Initial findings indicate that the sinkholes in northern Mitchell, IN, where the Blue River Group is visible, tend to be deeper on average compared to other areas. XRF results show that St. Louis has the highest CaO₃ of 93.55% followed by the Salem and St. Genevieve limestones at 91.70% and 91.37% respectively.