EVOLUTION OF A GLACIER TERMINUS WITH IMPLICATIONS FOR LOCATING STAGNANT ICE

We use field observations and satellite imagery of the terminus of Emmons Glacier, Mount Rainier, WA to locate stagnant ice, and to understand the evolution of the glacier terminus in response to declining mass balance. Emmons Glacier is the largest glacier on Mount Rainier, and supplies the White River, a tributary of the Puyallup River Watershed. Analysis of satellite imagery since 2006, available through the National Agricultural Imagery Program, shows 103 m of terminus retreat at the centerline of the glacier, compared to 87 m of retreat on the western margin and 73 m of retreat on the eastern margin. Preliminary analysis of proglacial sediment on the valley floor, immediately in front of the western glacier margin, suggests the deposition of angular supraglacial debris; while subglacially transported debris dominates proglacial sediment in front of the glacier centerline, where the White River emerges. Satellite imagery of this midpoint shows a widening ice face, consistent with a lowering ice slope at the terminus. We interpret the length of this ice face as an approximate limit of active ice flow at the glacier terminus, which represented ~20% of the total length of the 2019 terminus margin. Subglacial meltwater streams emerging from the terminus have been limited to this active portion of the terminus since 2006. Although seasonal variation in the location of these channels is not fully captured in satellite imagery analyzed for this study, there is limited remote sensing or field evidence of substantial and sustained meltwater release from the eastern and western margins since 2006. Our findings suggest that Emmons Glacier ice is stagnating at the terminus front. Continued negative glacier mass balance will likely result in the expansion of stagnant ice, and increased concavity of the glacier terminus margin.