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80-4 Spatial variations in subglacial erosion determined by paired cosmogenic nuclides, southeastern Alaska

Session: Recent Advances in Glacial Geology, Geomorphology, and Chronology

Presenting Author:

Jeremy Brooks

Authors:

Brooks, Jeremy Patrick¹, Jones, Andrew², Marcott, Shaun³, Zoet, Lucas⁴, Lifton, Nathaniel⁵

(1) Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA, (2) Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA, (3) Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA, (4) Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA, (5) Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA; Department of Physics and Astronomy, Purdue University, West Lafayette, IN, USA,

Abstract:

Bedrock erosion by glaciers shapes alpine landscapes, produces vast sediment yields, affects ice dynamics on long timescales, and generates fresh mineral surface area for chemical weathering reactions. Despite the importance of glacial erosion as a geomorphic process, quantifying rates and spatial patterns of glacial erosion has remained enigmatic. Here, we use measurements of in situ ¹⁰Be and ¹⁴C to determine glacial erosion rates during Holocene ice cover for an alpine glacier in southeastern Alaska. We focus on two spatial scales: valley-scale erosion in which we collect samples across the ~2 km² glacier forefield, and landform-scale erosion where samples were collected along a ~100 m longitudinal transect of a roche moutonnée. Bedrock samples (n = 27) collected across the glacier forefield reveal substantial variations in abrasion rates, ranging from <0.01 mm/yr to ~0.7 mm/yr, which are consistent with the inferred Holocene ice history and nuclide measurement uncertainties. A subset (n = 7) of these samples collected along the roche moutonnée transect include upstream abraded surfaces and downstream quarried surfaces, to quantify the relative efficiency of the two erosional processes. Our results suggest that the vertical rate of quarrying is at least five times greater than the abrasion rate at this location. We identify an order-of-magnitude discrepancy in erosion rates determined from cosmogenic nuclides compared to studies using proglacial sediment volumes in southern Alaska, and suggest that both methods may not accurately measure basin-averaged glacial erosion rates due to measurement biases. This work suggests that subglacial erosion rates are highly variable based on local glaciological factors, with implications for glacial landform development and landscape evolution modeling.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7106

Spatial variations in subglacial erosion determined by paired cosmogenic nuclides, southeastern Alaska

Description

Session Format: Oral

Presentation Date: 10/20/2025

Presentation Start Time: 09:05 AM

Presentation Room: HBGCC, 213AB

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