Using electrical resistivity methods to map cave passages and conduits in the San Solomon Springs karstic aquifer system, West Texas, USA

Personnel with the National Cave and Karst Research Institute (NCKRI) have conducted a series of electrical resistivity (ER) surveys over and beyond mapped portions of Phantom Lake Spring Cave, currently the deepest underwater cave in the United States, and one component of the San Solomon Springs group, a network of karstic springs in far west Texas. Most of the cave is partially or completely flooded with slightly brackish water, and appears on ER profiles as a zone of low electrical resistivity. ER surveys show electrically conductive zones indicative of a flooded conduit up to 400 m beyond the farthest downgradient station in the mapped portion of the cave. A dye trace study conducted in 2013 suggests that water in Phantom Lake Spring Cave flows at a rate of 1000 m/day through conduits formed in Cretaceous limestone, eventually discharging from San Solomon Spring at Balmorhea State Park, six kilometers east of the cave entrance. Low resistivity anomalies identified on an ER survey conducted ~400 m west of the park probably represent those flooded karstic conduits, confirming the hydrologic link between Phantom Lake Spring Cave and San Solomon Spring.