ELECTRICAL RESISTIVITY INVESTIGATIONS OF KARST FEATURES NEAR SPRINGFIELD, MISSOURI

Springfield, Missouri is located on the Springfield Plateau which is on the southwestern flank of the Ozark Dome. The Ozark Dome consists of carbonate and siliceous strata uplifted mainly in the Late Paleozoic. In the Springfield region, the Paleozoic units consist mainly of nearly horizontal Mississippian carbonates including the Burlington Limestone which were fractured during the uplift of the Ozark Dome. Some of these fractures over time have been enlarged due to groundwater flow and thus have led to the development of karst geomorphological features including caves, sinkholes and solution valleys. The development of new sinkholes within the Mississippian carbonates is a reoccurring problem in urban areas in and surrounding Springfield. Recently, new sinkholes have been developing in a region in south Springfield near the city of Nixa. These sinkholes are relatively small (a few to ten meters wide) but are occurring in residential areas and may lead to houses being abandoned. To investigate the size, geometry and depth of these sinkholes, a series of direct-current electrical resistivity surveys were conducted. The surveys which were performed using the Schlumberger array were conducted over areas with exposed sinkholes. The main problem in conducting electrical surveys in residential areas is that one cannot obtain a large electrode spacing that allows one to image deep enough to determine the depth of the sinkhole. Due to cultural influences (e.g., fences, houses, sidewalks, electrical cables/lines, streets) we could not have the current electrode spacing large enough to image below 15 to 20 feet the surface. However, in several environments, if the sinkhole is near the surface, one can determine the lateral extent of the developing sinkhole and the electrical resistivity survey can add valuable information in planning any actions in controlling the enlargement of the sinkhole. The electrical resistivity survey in south Springfield over an exposed sinkhole imaged the lateral extent of the sinkhole based on excavations of the sinkhole. Two dimensional inversion of the data showed that the sinkhole is approximately 3 meters wide and 4 meters deep. Additionally, a small region of low electrical resistivity values were imaged that may represent presently developing karst features.