INVESTIGATING SUBGLACIAL ENVIRONMENTS AT MOUNT RAINIER, WASHINGTON USING SUSPENDED SEDIMENT CONCENTRATIONS AND HYDROCHEMICAL ANALYSIS

We use hydrochemical and suspended sediment analysis of glacial meltwater from Mount Rainier, Washington to investigate subglacial environments, including hydrothermal influence, weathering and erosion processes, and sediment storage. Mount Rainier thermal springs contain high levels of sulfate and chloride; we interpret the presence of these anions in glacial meltwater as indicators of subglacial hydrothermal influence. We expect to see higher concentrations of subglacially-supplied sulfate and chloride during diurnal lows in meltwater discharge, when the supply of snowmelt to glacial meltwater is low. Data collected in the summers of 2012-2016 suggest that increased production of suspended sediment is associated with hydrothermally-altered bedrock beneath the glacier. Meltwater from Tahoma glacier, which originates from an area known to be hydrothermally altered, yields consistently higher levels of chloride and sulfate, and of suspended sediment relative to other glaciers. Additional analyses of Emmons, Winthrop, and Carbon meltwater will provide a more detailed assessment of subglacial environments on Mount Rainier. We expect meltwater from Winthrop and Emmons glaciers to contain relatively high levels of sulfate and chloride due to their proximity to hydrothermally-altered bedrock. We also hypothesize that suspended sediment concentrations will decrease toward the end of the ablation season due to the melting of subglacial pockets that store suspended sediment during the accumulation season. Our work will inform ongoing efforts to understand sediment transport and geologic hazard risk in Mount Rainier National Park.