USING RESISTIVITY TO CHARACTERIZE PAST AND PRESENT GROUNDWATER FLOE IN A KARST SETTING TO BETTER UNDERSTAND THE FORMATION AND EVOLUTION OF OWL CAVE AND WATER SINKS COMPLEXES IN HIGHLAND COUNTY, VA

The evolution of cave systems in karst is a complex process, driven by the distribution of soluble rocks in the subsurface, the pathways within which water collects and flows, and constraints of the geological structure. While the caves themselves can be explored, many factors controlling their evolution are hidden in the subsurface, making the process difficult to ascertain. By extracting this information, we will be better able to understand not only how the cave systems formed and changed overtime, but how they are likely to evolve going forward, allowing for a more accurate understanding of, and mitigation of, potential hazards.

We collected several datasets using electrical resistivity tomography (ERT) in the area around Owl Cave and Water Sinks, with the purpose of characterizing the resistivity structure of the subsurface along profiles chosen to give insight into past and present groundwater flow. Features with very low resistivity (<50 ohm-meters) suggest active water flow, whereas features with very high resistivities (~100,000ohm-meters) indicate void spaces, and therefore may illuminate potential water flow pathways that are no longer active.

Interpreting the resistivity cross-sections within the framework of the regional geology, we are able to piece together the pathways for water flow in the past and present, and from that, develop an understanding of the development of the cave systems in the area. We concluded that within the anticlinal structure, an impermeable layer of sandstone embedded within the limestone served as the primary constraint to water flow, and that the dipping of this layer caused the water pathways to migrate laterally as they deepened, driving the overall evolution of the system.