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
Reconstructing a Late Pleistocene ice cap in the Salmon River Mountains, western Idaho, U.S.A.
Paper number: 16-2
Program: Technical Sessions
Time: 3:40 PM – 4:00 PM
Authors
Abstract
The Northern Rocky Mountains of the western United States feature a rich geologic record of Quaternary glaciations. Glacial deposits and landforms in the Salmon River Mountains of western Idaho have afforded reconstructions of ice extent and thickness near the margins of Pleistocene mountain glaciers. Reconstructions of ice extent in accumulation areas have been more challenging, however, due to the complex geometry of large ice cap-outlet glacier systems. Lidar-based digital terrain models can reveal glacial geomorphological features where detailed reconstructions are missing, providing key imagery for mapping glacial features and delimiting the full extent of mountain glaciation. This study maps the glacial geomorphology of a large area centered on the Landmark basin in the western Salmon River Mountains. Here, an assemblage of streamlined glacial-erosional landforms represents a pattern of ice flow across drainage divides, indicating that the Landmark basin featured a thick ice cap with numerous outlet glaciers in the headwaters of the Payette and Salmon Rivers. The largest outlets formed piedmont glaciers in neighboring intramontane basins, including the well-preserved moraine complex impounding Warm Lake ~30 km northwest of Cascade, Idaho. A map-based reconstruction of the Landmark ice cap has a planimetric surface area of 1140 km2 and a thickness exceeding 400 meters near the center of the ice cap. The northern outlet of the ice cap terminated near Yellow Pine, Idaho, and the southern outlet terminated 6 km north of Deadwood Reservoir. Moraines deposited along the margins of more than 20 outlet glaciers are multi-crested and feature abundant granitic boulders suitable for cosmogenic exposure dating, affording an opportunity to reconstruct the evolution of the ice cap and the timing of Pleistocene glaciation in western Idaho.
Geological Society of America Abstracts with Programs. Vol. 58, No. 4
doi: 10.1130/abs/2026RM-410693
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