Geomorphological Analysis of Longhorn Cavern in Burnet County, Texas via Integrated Ground and Airborne LIDAR Data

Longhorn Cavern is located within Burnet County, Texas in the Llano Uplift region. Longhorn Cavern encounters flooding via water percolation through the cavern ceiling from water discharging through sinkholes on the surface. This paper focuses on the four key topics which are: (1) generate an accurate and high-resolution 3-dimensional model of the cavern from a TLS (Terrestrial Laser Scanning) survey to provide a surface expression of it, (2) produce meshes from the collected data of the cavern for volumetric calculations of the cavern itself and the volume of the strata between the surface and cavern ceiling (3) characterize sinkholes within the area underneath the forest canopy, and (4) to delineate the water percolation/cover collapse zones from these sinkholes through a cavern to surface expression. To build a 3-dimensional model of the cavern, a LIDAR survey was performed in this study. TLS data was collected over the span of 3 days that was composed of 39 scans throughout Longhorn Cavern from the Sam Bass Entrance through the Hall of Gems room. The output of this LIDAR data was a high-resolution 3-D model of Longhorn Cavern containing a point density 457 points per m2 and a length of 460 m. The average standard deviation error is 2.21 between registered scans. Meshes were generated from this point cloud and the volume of the cavern was 16,035.47 m3. The volume of the strata above the cavern was 287,058.38 m3. 1-meter aerial LIDAR data of the surface around Longhorn Cavern was downloaded from the USGS 3-DEP project database, and a DEM was generated from it to delineate sinkholes around Longhorn Cavern State Park. 3 high-risk sinkholes water percolation/cover-collapse zones were discovered which include Sinkholes 28, 29, and 39. The volume above the cavern for sinkhole 28 is 13,254.21 m3, sinkhole 29 is 7,411.16 m3, and sinkhole 39 is 3,450.99 m3.