STATUS OF KARST MAPPING IN OHIO

The Ohio Department of Natural Resources, Division of Geological Survey (the Survey) is in its seventh consecutive year of karst mapping, and the current work is revealing intriguing karst features previously unseen in the state. Regions with karst and potential karst are readily identified using a 2.5 square feet per pixel digital elevation model (DEM) with 6 inch vertical accuracy derived from light distance and ranging (LiDAR) data. Field checking of these features validates the DEM-derived features and often leads to the discovery of new features. Analysis of the DEM in the Sinking Spring 7.5-minute quadrangle of south-central Ohio suggests 2,030 potential karst features to field visit. Of these, a total of 713 sinkholes, 32 springs, and 263 suspect points have been field visited and mapped so far, making the Sinking Spring quadrangle the most karst-dense quadrangle the Survey has mapped to date. This recent field work near Sinking Spring, Ohio, has located some interesting karst features that may be partly controlled by past glaciation. In this part of the state, springs are frequently found down slope from sinkholes where water percolates down through the dissolutioned carbonate bedrock, encounters shale, and travels laterally. However, some springs have been located further up slope than the sinkholes they drain into. This may indicate irregular subsurface flow, perhaps caused by till deposits of variable thickness or variability in solution patterns. Another unique characteristic of the sinkholes in this region is the tendency to cluster along valley rims, likely controlled by a combination of bedrock position relative to topography and till thickness. In the same area, a few deep karst bedrock fractures were encountered that appear to have infilled with till and later reactivated, which is interesting because they may be indicative of the timing of karst activity versus glaciation.