UTILIZING ELECTRICAL RESISTIVITY TOMOGRAPHY (ERT) TO INVESTIGATE UNDISCOVERED CAVE CONNECTIONS IN HIGHLAND COUNTY, VIRGINIA

Burnsville Cove, Highland County, Virginia is home to many known cave systems. There is evidence that two of these, Helictite and Wishing Well Cave, are connected by undiscovered subsurface conduits. The drainage system that feeds the nearby Emory Spring is unknown but studies have shown that it likely flows through an open conduit that doesn’t allow for chemical exchange between the water and ground. Furthermore, airflow detected in Wishing Well Cave suggests that there are connections that allow for air exchange. We conducted an Electrical Resistivity Tomography (ERT) survey within an area of interest characterized by multiple sinkholes on the surface between the two cave systems. ERT finds the resistivity of the subsurface by injecting currents and measuring the voltage drop between different configurations of electrodes, generating a grid of apparent resistivities. This can be correlated to rock units, void spaces, and zones of water saturation. Three lines were collected consisting of 56 electrodes each over the area of interest. Dipole-Dipole and Schlumberger arrays were collected to produce a merged data set with better lateral and vertical resolution. The data was processed with EarthImager 2D, a software that generates a continuous resistivity image using inversion modeling. The first line was over known passages of Wishing Well to constrain how it appears in the inversion. The other two lines were near the boundaries of each system to understand how any void spaces might connect. Placement was also guided by the sinkholes in order to better reveal connections between any void spaces and the surface. We found anomalies that suggest the presence of both a resistive region of high porosity, possibly capable of air exchance. As well as a region of high conductivity that might indicate a permeable water saturated connection. Future work includes additional lines to investigate less direct paths between the cave systems, and longer lines to identify void spaces deeper from the surface.