CROSSING BOUNDARIES ON PUBLIC LANDS: AN UPDATE ON GEOPHYSICAL SURVEYS OF A POTENTIALLY EXTENSIVE CAVE SYSTEM UNDERLYING BLM AND NATIONAL PARK SERVICE UNITS

During the spring, 2015 field season National Cave and Karst Research Institute (NCKRI) personnel conducted a microgravity survey over Big Manhole Cave, located on public land administered by the US Bureau of Land Management in the Guadalupe Mountains of southeastern New Mexico. Big Manhole is a relatively shallow pit cave, and is thought by many cavers to be a second entrance to Lechuguilla Cave, the deepest cave in the continental United States. Digging in Big Manhole has been occurring sporadically for many years, following airflow through cemented breakdown. Microgravity survey results indicate a negative gravity anomaly southwest of the cave entrance, consistent with results of a 3D resistivity survey conducted in the area by NCKRI staff in 2012-2013. Combined geophysical results suggest the presence of a substantial void in the subsurface a few tens of meters below and extending to the south of the dig. The entrance to Big Manhole Cave is located <300 m north of the Carlsbad Caverns National Park boundary. Lechuguilla Cave is located within the Park, but at its northeasternmost point Lechuguilla is only 300 m from BLM administered land. If a connection is established between Big Manhole and Lechuguilla Caves, it will raise interesting questions about dual management of this unique natural resource.