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

Multiple glacier advances during the Late Pleistocene and Holocene in the Trinity Alps, Klamath Mountains, CA

Paper number: 16-0
Program: Technical Sessions
Time: 3:00 PM – 3:20 PM

Authors

Abstract

Late Quaternary glacial history is well documented across many of the mountain ranges of the western United States.  A notable exception is the Klamath Mountains in northern California, where u-shaped valleys, cirques, and moraines attest to a rich but unquantified glacial history. This study provides 32 new 10Be exposure ages from 3 glaciated valleys in the Trinity Alps wilderness: Sugar Pine, Upper Coffee Creek, and Grizzly Creek.   Detailed Quaternary mapping combined with cosmogenic exposure age-dating and tree-ring analysis reveals 4 distinct sets of moraines: pLGM,  LGM-max, LGM-l,  and Holocene.  ELAs calculated for these paleoglaciers are 1960±65 (pLGM), 2020±50 (LGM-max), 2090±60 (LGM-l), and 2400±100 (Holocene) meters, making them much lower in elevation than other paleoglaciers in CA for the Pleistocene.  10Be cosmogenic exposure ages from pLGM boulders (n=8) have a median age of 40.4 ka, although ages range from 15.6-125 ka, implying significant post-depositional erosion of these moraines. LGM-max boulders (n=7) have a 10Be median age of 19.9 ka, with 5 boulders clustered between 18.3-20.2 ka.  LGM-l boulders (n=7) have a 10Be median age of 15.6 ka, with 4 boulders clustering between 13.5-15.9 ka.  Five boulders from Holocene moraines provide 10Be exposure ages between ~0.2-7.5 ka. The oldest trees growing on the older (outer) and younger (inner) Holocene moraines provide minimum ages for glacier advances 1296-1391 and 1845-1940 C.E., respectively, and suggest Holocene glacier advances may be synchronous with the start and end of the Little Ice Age.   Together, these data imply at least four distinct glacial episodes: 1) pre-LGM glaciers may represent pre 130 ka ages but may also incorporate glaciers between ~80-40 ka, 2) LGM-max glaciers that reached their maximum extent 20.2-18.3 ka and shrank after 18 ka into the upper portions of the valleys, 3) LGM-l glaciers represent a re-advance of valley glaciers to ~75% of their LGM-max length at ~15.6 ka, followed by slow retreat until at least 13 ka, and 4) at least 2 late Holocene glacier advances are confined to the highest cirques ~675 and 125 years ago, although other late Holocene advances are suggested by our cosmogenic ages. These ages reflect slightly later and much lower elevation glaciers than elsewhere in CA for the same time period.

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

doi: 10.1130/abs/2026RM-410563

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