SUPRAGLACIAL DEBRIS EXTENT AND MASS-BALANCE IMPACTS ON EMMONS GLACIER, MOUNT RAINIER

Emmons Glacier is one the largest glaciers in the lower 48 states, dominating the iconic view of Mount Rainier from Sunrise. While most of the mountain’s major glaciers have thinned or retreated since 1970, the Emmons Glacier terminus has thickened. This anomalous behavior—which is mirrored by the adjacent Winthrop Glacier—has typically been attributed to the blanket of supraglacial rock debris on Emmons Glacier’s terminus, which is expected to insulate the underlying ice. Mass balance effects of supraglacial debris depend strongly on the thermal properties and thickness distribution of the debris, neither of which is well constrained for Emmons Glacier. We combined field measurements and satellite remote sensing analysis from a ten-day period during the 2014 melt season to estimate both the debris thickness distribution and key debris thermal properties on Emmons Glacier’s terminus. An ablation stake network and temporary weather station were used to measure the dominant energy fluxes along with elapsed melt of the underlying ice in a small (60 m by 60 m) area of the terminus. Measured sub-debris ablation rates were compared with rates computed in a simplified energy balance model to estimate debris thermal conductivity. The same energy-balance model was then used with debris surface temperatures derived from Landsat 8 thermal infrared bands to estimate the distribution of debris thickness across the entire debris-covered terminus. The resulting map of thermal resistance can be used to inform projections of mass balance and runoff changes.