16 Understanding the Past and Present Cryosphere of the Rocky Mountains

Alpine snow and ice play seminal roles in the environmental, geomorphic, and hydrologic processes. This session welcomes abstracts on scientific studies of the past and present cryosphere in the Rocky Mountains and beyond.

Monday, 18 May 2026
3:00 PM - 5:30 PM
Alvarado C

Variable rates of glacier retreat after 16 ka in the Trinity Alps of Northern California from new 10Be exposure dating of glacial landforms

Paper number: 16-1
Program: Technical Sessions
Time: 3:20 PM – 3:40 PM

Authors

Abstract

The Trinity Alps of northern California provide evidence for glaciers in the late Pleistocene, yet few chronologies exist for this range. This study focuses on the Stuart Fork Valley within the Trinity Alps Wilderness. We document the timing of the last Pleistocene glacier advance and retreat by combining new mapping with ten new 10Be cosmogenic exposure-ages. Five boulders were sampled from a prominent set of moraines located 9.3 km down valley from the cirque, representing the last major glaciation of the Stuart Fork Valley. Four boulders range from 14.3 ka to 16.3 ka and provide an inverse-variance weighted mean of 15.7 ± 0.4 ka, with one boulder excluded (27.3 ka) because it is assumed to have inheritance. Five bedrock samples collected from the valley floor and an adjacent high-elevation plateau constrain the timing of glacier retreat from ~15.7 ka to ~8.6 ka. Rapid ice loss and glacier shrinkage occurred from 15.7 ka to 15.2 ka with an average rate of ~5.8 m/yr. From 15.2 ka to 13 ka, glacier retreat decreased to 1.7 m/yr.  Shrinkage slowed even more between ~13 and 10 ka to 0.5 m/yr. This data suggests that although glaciers in the Trinity Alps retreated rapidly immediately after 15.7 ka, the rate decreased at 15.2 and again at 13 ka, and ice remained on the north-facing valley slopes until at least 8 ka.  We infer the slow rates of early Holocene retreat to be due to topographic shielding combined with a wet climate due to the close proximity of the Trinity Alps to the Pacific Ocean, despite rising temperatures.  These results provide new data for understanding the variability of late Pleistocene climate change in the western US. 

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410569

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