122 From the Cosmos and Back: Quantifying Processes and Rates of Landscape Change

This session explores how methods such as cosmogenic nuclides, apatite (U-Th)/He thermochronometry, U-series geochemistry, luminescence, and chemical mass balances quantify relationships between climate, tectonics, and erosion.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 212AB

Using High-Resolution ¹⁰Be Exposure Ages to Track Deglaciation Dynamics in the Eastern Sierra Nevada

Paper number: 122-9
Program: Technical Sessions
Time: 3:50 PM – 4:10 PM

Authors

Abstract

Reconstructing past glacier dynamics is key to understanding late-Quaternary climate change and landscape evolution in alpine environments. Traditionally, glacier chronologies have relied on cosmogenic nuclide dating of moraines, which constrain ice extent but provide limited insight into the dynamics of glacier retreat. Here, we present densely sampled ¹⁰Be exposure ages from exposed bedrock surfaces along elevational transects in two adjacent catchments in Bishop Creek, eastern Sierra Nevada (California). This approach allows for a more nuanced reconstruction of ice extent and an examination of the pacing of deglaciation.

Our results show that calculated exposure ages from both basins are consistent along the transects and younger than established moraine-based chronologies. We interpret this offset as a signature of post-depositional erosion and applied two site-specific end-member scenarios (surface rock and till erosion) to correct exposure ages. The corrected results indicate that valley glaciers in Bishop Creek persisted >5 km downvalley until ~13 ka, significantly farther and later than previously recognized. Minimal variation in exposure ages across both catchments suggests rapid retreat over a period of several hundred years during the Recess Peak deglaciation. These findings challenge the prevailing view that post-LGM (Tioga 4) glaciation in the region was limited to small cirque glaciers. Instead, our results show that valley glaciers in Bishop Creek remained more extensive and underwent abrupt retreat after the Recess Peak glaciation (14-13 ka).

Our study presents a novel approach for reconstructing glacier retreat using bedrock sampling and erosion-corrected ¹⁰Be exposure dating. This method complements moraine-based chronologies and is especially useful in landscapes where moraines provide an incomplete or ambiguous record of glacier retreat. It holds broad potential for reconstructing glacier dynamics during periods of climatic change in other previously glaciated alpine regions.

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

doi: 10.1130/abs/2025AM-413811

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