16-18 Mapping Multi-level Cave Systems Using Ground Penetrating Radar in South-Central Pennsylvania’s Cumberland County

Session: From Thin Section to Outcrop: Exploration of Undergraduate Research (Posters)

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Abstract:

During 2023 and 2025, PASSHE Geology Field Course students used GPR to map subsurface karst architecture at two cave systems in south-central PA: Carnegie Cave (CC) and Black Coffey Caverns (BCC). Surveys were conducted using a MALA X3M with 250- and 100-MHz antennas. At BCC, data was collected from the surface and from within cave passages. The primary goal was to determine whether GPR could resolve known cave levels and identify voids beneath karst depressions.

Initial surveys at CC demonstrated the ability of GPR to image at least 4 stacked cave horizons, including at least four discrete cave levels, two of which were mapped. These results guided more targeted investigations at BCC during the 2025 field season. At BCC, surface GPR profiles were collected parallel and perpendicular to the strike of steeply dipping limestone units. Three profiles, oriented parallel to strike, were collected along Williamson Road, and thirteen were collected ~E-W across bedding. Individual transects averaged 34 m in length. Four underground transects totaling 138.5 m were collected along cave passages at two cave levels. Underground profiles ran within high-purity limestone beds or within fracture intensifications.

At BCC, the cave lies beneath a complex of closed depressions (~33, 44, and 60 m in E-W length). The largest exhibits ~2 m of surface relief. Transect T17 begins in the upper cave level at ~530 ft elevation, extends southward beneath the central sinkhole down to ~524 ft at it lowest point. Surface GPR data reveals it is ~6 m below ground. T20 was collected within the second conduit level. Its sump was at an elevation of ~502 ft (~7 m below the upper passage). T20 data reveals deeper anomalies/voids down to at least ~482 ft elevation. The elevation of Conococheague Creek is at ~469 ft, where cavers identified a smaller cave system, indicating the presence of a 4th cave level. 

Our mapping thus reveals that BCC is a complex, vertically integrated karst conduit system. Together, surface and underground GPR data document significant vertical separation between cave levels and reveal laterally extensive, unexposed voids beneath the sinkhole complex. These results demonstrate the effectiveness of GPR for mapping multi-level karst systems and highlight the strong structural and hydrologic controls governing cave development in the Cumberland Valley.

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