RESISTANCE IS NOT FUTILE: GEOPHYSICAL SURVEYS OF KARST FEATURES USING ELECTRICAL RESISTIVITY, SPRINGFIELD, MISSOURI

Springfield, Missouri is located on the Springfield Plateau which consists of Paleozoic carbonate and siliceous rocks with a thin soil cover. The uppermost exposed unit is the Mississippian Burlington Limestone, a nearly horizontal carbonate layer which is susceptible to karst formation. Karst features such as caves and sinkholes present hazards for engineering and groundwater contamination. An understanding of the location, size and geometry of these features is needed to adequately manage and prepare for karst related hazards. The James River Freeway/US-160 Interchange in Springfield is within close proximity to sinkholes, caves, and springs, and therefore a location of concern for future karst hazard formation.

Geophysical surveys using electrical resistivity were implemented to study known karst features and to better understand groundwater flow and overall karst geology of the area. Two-dimensional resistivity profiles using the Schlumberger array with electrode spacing of either 1 or 2 meters were used. The features surveyed include a water-filled cave, a newly forming sinkhole, and a bedrock hillside containing perennial springs. Results of surveying the cave verify electrical resistivity detects water-filled voids with accurate depth. The newly formed sinkhole is detected as a low resistivity zone which extends to the subsurface but which then trends laterally away from the center into another discrete resistivity low, likely a water and soil saturated conduit that remains detectable even without recent precipitation. Discharge of groundwater through springs at the bedrock hillside appears to be through widened conduits along a bedding plane. Urban geophysical noise sources, specifically power lines, were also observed and investigated for future resistivity surveys to consider. Along with dye traces performed at these karst features a greater insight into local geology and hydrology has been made which can be used to better assess karst hazards.