GLACIER MELTWATER ANALYSES AT MOUNT RAINIER, WA

Mount Rainier, a stratovolcano in Washington State, is one of the most glaciated peaks in the conterminous United States and as such offers opportunities to study interactions between volcanic and glacier hydrologic processes. This presentation will share geochemical analyses of Mount Rainier glacier meltwater. Samples were collected during the ablation season over the last eight years; when possible, samples were collected at sufficient frequency over consecutive days to capture diurnal variations. Analyses include concentrations of sulfate and chloride, suspended sediment, and bicarbonate measured in samples collected by hand; as well as pH, electrical conductivity, and water temperature measured by a multiparameter probe. Our results reveal glacier hydrologic systems extremely sensitive to atmospheric changes; diurnal temperature changes can cause stream levels to fluctuate by tens of centimeters overnight, in some instances altering the stream channel morphology. Increased stream discharge appears to dilute hydrothermal influences, but meltwater samples collected during diurnal discharge minima yield low levels of sulfate and chloride in some instances. Based on analyses of thermal spring waters, we interpret these concentrations as indications of hydrothermal influence on the subglacial environment. Regions of the mountain with more extensive hydrothermal alteration yield meltwaters with higher levels of sulfate and chloride. Nevertheless, these systems are dominated by atmospherically-derived waters during the ablation season; an inversely proportional relationship between electrical conductivity and meltwater discharge, and bicarbonate analyses suggest atmospherically-dominated glacier hydrologic systems with limited water storage in the subglacial environment.