Accelerating rates of glacier change and topographic controls, Glacier National Park, MT, USA: 1966-2021

Changing mountain glaciers impact downstream hydrology and alpine ecosystems and provide tangible evidence of climate change to the broader public. Recent advances in photogrammetry and remote sensing data availability allow these changes to be quantified at regional spatial scales. In turn, explaining glacier-to-glacier variability over multi-decadal time scales has only recently become possible due to advances in data availability and technology. In this study, we use historical aerial photographs, modern satellite stereo imagery, and LiDAR data to quantify area, volume, and mass change at 35 glaciers within Glacier National Park, MT, USA from 1966-2021. All 35 glaciers lost area and volume over the 55-year study interval. Collectively, regional glacier mass loss was -0.21 ± 0.07 Gt representing a 46% decrease in the region's total previously estimated ice volume. Glacier mass loss rates were faster over the period 2008-2021 than 1966-2008. Variability in glacier mass loss rates is likely explained by topographic controls, such as elevation distribution, glacier aspect, clear sky radiation, snow avalanches, and wind redistribution of snow. The greatest rates of glacier volume change in the region are observed at Grinnell Glacier where lake calving processes influence glacier mass balance. The USGS Benchmark Glacier (Sperry Glacier) in the region shows rates of mass loss that are 160-170% higher than the average mass loss rate of the region, suggesting a need for caution when regionalizing in situ glaciological records of glacier change.