Multi-annual measures of rock glacier-wide volume change and surface kinematics in Great Basin National Park

Abstract:

Mid-latitude, mountain glaciers are important freshwater resources and sensitive indicators of alpine climate change. Great Basin National Park is home to the only mapped glacier in the state of Nevada, the Wheeler Peak Glacier (WPG), a debris-covered glacierette situated above the Lehman Rock Glacier (LRG). These two landforms share a sheltered north-facing cirque and are the most pronounced extant cryospheric features in the Snake Range. They play a significant role in alpine sediment cascade and are likely important sources of base flow for the alpine lakes and streams below that provide specialized habitat for endemic species. Across the mid-latitudes, the kinematical behavior of rock glaciers is changing due to permafrost sensitivity to air temperature increases– magnifying interest in characterizing rock glacier kinematics alongside volumetric change. Beginning in 2015, our group has undertaken annual geodetic surveys of the LRG to measure volumetric and kinematic changes across its tongue-shaped surface using terrestrial dGNSS and aerial photogrammetric observations. Here we describe the geomorphology and inter-annual kinematics of the LRG as well as measures of surface velocity and volumetric change between 2015-19. It is possible LRG kinematics have abruptly reactivated due to recent climatic perturbations, but we challenge previous classifications of the LRG as wholly relict. The younger upper lobe of the LRG exhibits the most activity and may be accelerating, whereas the older lower lobe appears relict. Co-registered DEM-differencing at sub-decimeter resolution reveal widespread patterns of surface lowering across the LRG and WPG, with a net rock glacier-wide volume loss of >45,953 m^3 between 2015-2019 and evidence of localized thermokarst feature development. We discuss these results and describe how our innovative student-led field observation techniques enable us to document alpine cryo-geomorphic dynamics at fine spatial-temporal scales to better understand the processes that drive them. Detailed topographic observations also provide insights into annual debris input as well as periglacial processes of cryoplanation, nivation, and long-term freeze-thaw cycling, thus improving our capability for predicting future landscape evolution in glaciated mountain environments.