MAPPING SUPRAGLACIAL DEBRIS ON EMMONS GLACIER, MOUNT RAINIER, WA

Debris-covered glaciers from around the world offer distinct environmental, climatic, and historical conditions from which to study the effects of debris on glacier-surface evolution. A rich literature on debris-covered glaciers exists from decades of field work, remote-sensing observations, laboratory studies, and modeling that are typically site specific but provide general understanding about controls on glacier melting. In general, for the ablation zone of a glacier to be covered by more than ~50% debris, the debris flux needs to be relatively high and the ice-flow rate needs to be relatively low; this is the case for many Mt. Rainier glacier termini. In the lower regions of these glaciers the debris cover acts to insulate or enhance melting of underlying glacier ice. On Emmons Glacier we know that the debris cover, and especially rockfall from a 1963 avalanche, has insulated the lower glacier. However, heterogeneities in debris-cover thickness and character have led to significant (up to multi-meter scale) heterogeneities in surface elevation. We are particularly interested in how different terrain sources and different clast sizes may influence the efficiency of ice insulation. In order to address how debris cover controls the evolution of the lower Emmons Glacier, we are mapping supraglacial debris units to constrain the source, character, and movement of the sediment. During summer of 2016 we assessed sediment cover thickness, composition, size, sorting, as well as site temperature, slope angle, and if there were any stagnant ice formations along two transects at two different elevations across the width of the lower glacier. Some key results from 2016 field work include finding 1) more fine-grained sediment at lower elevation, 2) more angular grained sediment on the eastern side of the glacier where there was a rockfall event in 1963, and 3) fewer ultra-fine grained sediment near the center of the glacier. During summer of 2017, using visually derived differences in color and boulder density, we defined six surface-sediment units based on August 2016 satellite imagery and compared these units to sedimentological data collected in summer 2016.