INVESTIGATING SUBGLACIAL HYDROTHERMAL INFLUENCE ON MOUNT RAINIER, WA THROUGH HYDROCHEMICAL ANALYSES OF GLACIAL MELTWATER

Mount Rainier is a glaciated stratovolcano in the Cascade Volcanic Arc in Washington State. In this study, we analyzed meltwater from Nisqually and Emmons Glaciers to determine the influence of the mountain’s hydrothermal system on the subglacial environment. Because thermal springs on Mount Rainier contain elevated concentrations of chloride and sulfate, the presence of these two anions in meltwater, as well as decreased pH values and increased electrical conductivity, were interpreted as indications that the subglacial environment is influenced by hydrothermal processes. Additionally, alkalinity titrations were performed to determine the relative amount of atmospheric input such as snowmelt. Samples collected from the Nisqually River contained Cl^- and SO₄^2- concentrations ranging from 0.80-0.94 ± 0.04 mg/L and 3.86-4.22 ± 0.04 mg/L, respectively. Emmons Glacier concentrations fell within the ranges of 1.28-1.41 ± 0.03 mg/L and 5.78-6.31 ± 0.03 mg/L for chloride and sulfate. Analysis of meltwater collected at the same locations in the summers of 2015 and 2016 yielded similar anion concentrations. Our results suggest that meltwater from Emmons Glacier is minimally influenced by hydrothermal processes, but more influenced than Nisqually Glacier meltwater. These findings are consistent with previous studies that (a) suggest that a large majority of the hydrothermally altered rock underneath Emmons Glacier was removed during the Osceola Mudflow, 5600 years ago, and (b) offer little evidence of hydrothermal alteration or activity beneath Nisqually Glacier.