DETECTING ROCK GLACIER MOVEMENT WITH UAS-BASED PHOTOGRAPHY AND TOTAL STATION SURVEYS, GREAT BASIN NATIONAL PARK, NEVADA

Great Basin National Park, located in the South Snake range of Nevada, is home to the Wheeler Peak rock glacier, an iconic feature within the park that may play an important role as a hydrologic resource for alpine and riparian ecosystems. Mechanics and movement of the rock glacier are difficult to measure, however, due to inherent challenges of detecting slow surface change. Movement of the Wheeler peak rock glacier was detected by repeat total station surveys in 2011-13, indicating that the more active upper lobes are shifting downvalley while the lower lobes remain comparatively stagnant. The application of unmanned aerial system (UAS)-based photogrammetry allows for more efficient surveying of a larger area than would be feasible to cover with the previously used total station survey methods. UAS surveys allow for the measurement of horizontal and vertical motion as well as volumetric change; the latter could not be quantified using total station surveying. In order to establish that observed differences between surveys are representative of rock glacier motion and not an artifact of inherent variation, it is necessary to analyze the reproducibility of UAS-based photography. In 2019, images were collected during three flights over the lower portion of the rock glacier using a pre-mapped flight path. Two flights captured nadir angle images and the final flight captured oblique angle images. Comparison of high resolution point clouds generated using these image sets indicate that variation is concentrated in regions of steep slopes and depressions, potentially related to decreased point cloud density which is often observed on sloped surfaces. Surface roughness along gradual slopes does not appear to be a source of variability between repeat surveys. We continue the discussion of challenges and potential solutions to detecting change on landforms with rough surfaces, overcoming these challenges is key to future of rock glacier monitoring and understanding alpine environmental change.