Cordilleran Section - 115th Annual Meeting - 2019

Paper No. 12-5
Presentation Time: 2:55 PM


FLOREA, Lee J., Indiana Geological and Water Survey, Indiana University, 611 North Walnut Grove Avenue, Bloomington, IN 47405 and TODD, Claire E., Department of Geosciences, Pacific Lutheran University, Rieke Science Center 158, Tacoma, WA 98447

The glacio-volcanic hydrologic system at Mt. Rainier, a stratovolcano in the Cascade Volcanic Arc, comprises a suite of geochemical interactions between rising volcanic gases, circulating groundwater, bedrock, and an overlying mantle of glacial ice. Both authors, first independently and now together, seek to expand upon earlier datasets to provide a blueprint for thermal and chemical monitoring of volcano activity. For example, PI Todd focuses on hydrothermal weathering on the flank of the volcanic edifice that mobilizes sulfate and chloride ions and how monitoring of those ions may lead to better prediction of locations and times of higher risk of glacial outburst floods. PI Florea, in contrast, focuses on the summit fumarole caves and how the water, fumarole gas, and ice chemistry in the crater are a product of water circulation in the upper edifice and crater.

In the August 2017 campaign, both authors collected samples from a suite of thermal springs, talus springs, end-glacial streams, fumaroles, drip waters, and glacial ice for geochemical and isotopic analysis. From all sample sites, the isotopic ratios of δ2H and δ18O were analyzed and compared to data from earlier studies. The δ2H and δ18O values of talus springs largely align with recharge originating from localized flow systems. Thermal springs and end-glacial streams are more depleted than their elevation would predict; a portion of their recharge originates from higher elevations. In the crater, fumarole moisture and drip waters in the glacial caves overlap and are narrower in range than glacial ice; in other words, from locally recycled moisture.

Three thermal springs (Paradise 1 & 2, Longmire) and one end-glacial stream (Winthrop) were additionally analyzed for dissolved ions, δ34S, and 36Cl/Cl and 129I/I. The Paradise thermal springs (7-70 mg/L Cl; 18-200 mg/L SO4) and the end-glacial stream (3 mg/L Cl; 13 mg/L SO4) returned similar δ34S values of +4‰, compared to the ~0.5‰ in summit fumaroles and the +15‰ from Longmire hot spring (200 mg/L Cl; 18 mg/L SO4). Ratios of 129I/I follow the same trend as δ34S, suggesting older waters contribute more to the thermal springs at Paradise. The 36Cl/Cl data are the inverse of 129I/I. This may seem contradictory, but it is important to note that, unlike 129I/I, modern 36Cl/Cl is lower today than during peak nuclear testing.