COUPLING HIGH RESOLUTION SURFACE AND SUBSURFACE POINT CLOUDS FOR CAVERN AND KARST MODELING, CHARACTERIZATION AND ANALYSIS

Accurately surveyed and high resolution surface and subsurface point clouds significantly improve the mapping and modeling of caves and karst. The detailed geometries and geomorphologies revealed by these digital outcrop models allows for rapid and thorough interpretation and analysis. Modeling multi-elevation data sets jointly presents the opportunity to characterize and interpret the rock mass between multiple levels of the environment, analyze the potential geological, hydrological and biological connections, and extrapolate this characterization into the surrounding unexplored geology.

To test the applicability of this methodology, two easily accessible caves in Southeast Arizona with surface and subsurface point cloud data were modeled, characterized and analyzed. Coronado Cave in Coronado National Memorial was laser scanned with millimeter scale resolution for the length of the primary passage and has publically available 3 meter lidar-based surface digital elevation model (DEM, raster/gridded bare-earth surface) for the ground topography. Kartchner Caverns State Park was scanned with millimeter scale lidar for the three main public rooms: the Rotunda, Throne and Big Rooms. For the ground surface of Kartchner, unlike Coronado, the point cloud was surveyed by an unmanned aircraft system (UAS, UAV, or drone) using photogrammetry processing. The centimeter scale point cloud data was then processed further into DEMs, digital surface models (DSM, mesh/vector all-points surface) and digital terrain models (DTM, mesh/vector bare-earth surface). All cave passages had centimeter scale 3D mesh surfaces created. On both the surface and subsurface terrain models, geometrical and geomorphological features were automatically and manually identified, digitized and extruded along their orientations.

Analysis of the linked models showed that many surface fault, fracture and karst geomorphology features connect to controlling cave features. The 3 meter resolution surface data for Coronado Cave was not high enough to reveal many surface features except near the two collapsed entrances. Kartchner Caverns had more solid linkages, with the Rotunda Room showing a conspicuous surface expression to match the room morphology.