RECONSTRUCTION OF A PALEO DEBRIS FLOW EVENT IN A LIMESTONE CAVE USING FIELD WORK, TERRESTRIAL LIDAR, AND CFD SIMULATION

In the New Discovery section of the Mammoth Cave System in Kentucky, USA, there is a deposit consisting predominantly of Big Clifty sandstone with a total volume of about 650 m³ that cavers have named Mt. Ararat. This is a chaotic, angular, matrix-supported, roughly inversely graded deposit with grain sizes ranging from silt-sized particles through boulders larger than 1 m on each edge, and thus is interpreted as a debris flow deposit. The grain sizes present correlate with high velocities flows inferred from paleoflow indicators including small scallops on exposed limestone adjacent to Mt. Ararat. In this work we provide results from three-dimensional Eulerian-Lagrangian computational fluid dynamics with discrete element modeled sediment transport simulations to support our hypothesis that a debris flow occurred in this passage of Mammoth Cave. In addition, estimates of slurry mass flux associated with this debris flow event are presented. Determination of the mechanism and timing for this event has implications for the geomorphic history of the Mammoth Cave system; behavior of debris flows in caves, narrow canyons, or other confined spaces; and evaluation of the relative contributions to cave development from mechanical and chemical erosion.