T265 Geologic Research in the Cascades: Understanding Glacier Change, Geologic Hazards, and Mountain Hydrology along an Active Margin in a Changing Climate (Posters)

Wednesday, 25 September 2024
8:00 AM - 5:30 PM
Hall D

MAGNETIC MINERAL FINGERPRINTS OF SEDIMENT SOURCES IN A PARTIALLY GLACIATED WATERSHED: A CASE STUDY OF THE PUYALLUP-WHITE RIVER WATERSHED, WA

Paper number: T265-7
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

As anthropogenic climate change accelerates glacial retreat, exposing subglacial sediment to erosion, sediment supply to glaciated watersheds is expected to increase. Where glacial and lowland sediment sources have distinct compositions, mineralogy can be used to trace glacial sediment fluxes. The Puyallup-White River watershed, a partially-glaciated system on the west side of Mt. Rainier, provides such an opportunity. Here we compare the mineralogy of fresh sediment from an upland source (Emmons Glacier) to that of potential lowland sediment sources, especially soils. The magnetic iron oxide mineralogy, in particular, appears to be distinctive: magnetic hysteresis characteristics suggests that glacial material, glacially-sourced suspended sediment, and Commencement Bay sediment are all characterized by a ~60:40 mixture of coarse multidomain to fine single-domain iron oxide particles, whereas soils contain a higher fraction of coarse iron oxides and possibly some ultrafine particles. Peak magnetic coercivities are similar for glacier and bay sediments (~20mT) but slightly higher for river sediments (~30mT). These patterns are consistent with a common iron oxide component in glacial and Commencement Bay sediments, distinct from that in soils. In addition, the magnetic susceptibility of the fine sediment fraction (a proxy for iron mineral concentration) is highest at the glacier and lowest in Commencement Bay. Emmons Glacier sediment specifically has a higher ratio of high-field to low-field magnetic susceptibility (>1%) compared to other sources, indicating a higher concentration of paramagnetic minerals, e.g. Fe-silicates, which are observed in scanning electron micrographs of magnetic separates. These distinctions point toward a “fingerprint” of glacial sediment characterized by fine Fe-oxides and abundant Fe-silicates (perhaps including silicate-hosted Fe-oxides). The glacial component is variably mixed with a lowland component characterized by coarse Fe-oxides and a higher proportion of Fe-free silicates. We expect these distinct source fingerprints to support the development of proxies for past ablation rates of Mt. Rainier’s glaciers.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-404936

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