Geologic Publications for Mount Rainier

Evolving supraglacial sediment sources and extent on a large debris-covered glacier

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Author(s): Karina Ramirez, Jose Jimenez, Claire Todd

Category: PRESENTATION
Document Type: Poster 265-1
Publisher: Geological Society of America Abstracts with Programs
Published Year: 2024
Volume: 56
Number: 5
Pages:
DOI Identifier: 10.1130/abs/2024AM-404509
ISBN Identifier:
Keywords:

Abstract:
Emmons Glacier on Mount Rainier, WA is the largest glacier by area in the conterminous United States; approximately one-fourth of its 11 km² extent is covered by supraglacial debris. Field and remote sensing observations have shown that (a) the debris cover is made up of distinct units; (b) the area of debris-covered ice is increasing, while total glacier extent has decreased since 1991; and (c) the area of less weathered supraglacial debris units near the centerline of the glacier are expanding at the expense of more weathered supraglacial debris units near the glacier margins. These observations suggest distinct debris sources with different rates of sediment delivery to the glacier surface. To identify the source and post-depositional evolution of the debris cover on Emmons Glacier, we combine remote sensing-based mapping of debris unit boundaries with field-based sedimentological observations such as relative weathering, clast size and angularity, and mineralogical composition. Preliminary findings show that infrequent or intermittent rockfall supplies weathered debris to the margins of the glacier, where ice velocities are slow to negligible; and active ice flow delivers subglacially- and englacially- sourced debris near the centerline of the glacier. The migration of debris unit boundaries suggests a transition from a rockfall-dominant debris supply to a primarily glacially-derived source of supraglacial debris. This finding is consistent with a series of well-documented rockfalls that buried the lower half of Emmons Glacier in rock fragments from Little Tahoma Peak in 1963. These events have implications for the future surface mass balance of the glacier: thick rockfall debris will preserve the glacier ice beneath it, but this effect may be limited to the glacier margins.

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Suggested Citations:
In Text Citation:
Ramirez and others (2024) or (Ramirez et al., 2024)

References Citation:
Ramirez, K., J. Jimenez, and C. Todd, 2024, Evolving supraglacial sediment sources and extent on a large debris-covered glacier: Poster 265-1, Geological Society of America Abstracts with Programs, Vol. 56, No. 5, doi: 10.1130/abs/2024AM-404509.