GOING, GOING, GONE? DECIPHERING THE MASS BALANCE OF VERY SMALL GLACIERS IN THE AMERICAN WEST

Very small glaciers (<0.5 km²) account for ~60–80% of all glaciers in mid- and low-latitude mountain ranges and are predicted to experience rapid mass loss in the coming decades due to their short response times and narrow elevation ranges. However, secondary mass balance processes (e.g., topographic shading and snow redistribution by wind and avalanches) can effectively decouple these glaciers from regional climate forcings, challenging our ability to predict their response. Previous studies have found widely varying sensitivities to late 20^th and early 21^st century warming for these glaciers, emphasizing the need for further research into the drivers of both seasonal and long-term mass balance of these glaciers. Here, we present preliminary findings from glaciers in Colorado and Wyoming, including Arapaho Glacier (AG) and Middle Teton Glacier (MTG). Ground-penetrating radar surveys in June 2021 and June 2022 on MTG revealed spatial patterns in winter mass balance that were shaped by wind redistribution and avalanching, as well as a mean ice thickness of ~30 m. On AG, we documented >20 m in thinning between an airborne lidar survey in 2005 and a UAV Structure from Motion survey in 2021, with a spatial pattern that reflects solar exposure. Lastly, we utilized airborne and satellite imagery to map accumulation area ratios (AARs) for ~10 glaciers across the region from 2013 to present. We found AARs to be exceptionally low in 2021 and 2022, with many glaciers reaching minimum values of 0.2 or less.