GEOPHYSICAL SEARCH FOR CONCEALED KARST NORTH OF BELLEVUE, OHIO

Streams are sparse near Bellevue, Ohio because karst in the Columbus Limestone drains the area to feed springs in Castalia and Sandusky Bay. However, on rare occasions, sinkholes north of Bellevue have acted as springs following episodes of heavy precipitation. We used micro-gravity and electrical resistivity in an attempt to map subsurface voids in the area where flooding in 2008 was most severe. Gravity was also measured at more widely spaced stations surrounding the study area. Although a dipole-dipole profile over Seneca Caverns (south of Bellevue) shows both air-filled and water-filled voids in the limestone, we discovered no similar geophysical evidence of voids along either of two long (690 m and 830 m) east-west resistivity profiles along roads north and south of the most striking sinkhole complex in the area. Resistivity lows are instead interpreted as sediment-filled karst. Except for sinkholes only a few meters across and broad but shallow circular depressions in many agricultural fields, most of the surface is characterized by glacial and shoreline features over 10,000 years old. These broad depressions might be ancient karst filled with glacial-age sediments rather than zones of developing karst.