CHRONOLOGY AND PALEOCLIMATE OF LATE PLEISTOCENE GLACIATION IN THE TRINITY ALPS, CALIFORNIA, FROM COSMOGENIC 10BE AND NUMERICAL MODELLING

Glaciers are sensitive indicators of climate variation, especially to changes in precipitation and temperature over sub-millennial timescales. The western United States exhibits an excellent record of glaciation, but ongoing work across the region shows complex and yet-unexplained variation in timing of deglaciation at the end of the Last Glacial Maximum (LGM). The Trinity Alps of the southern Klamath Mountains in Northern California contain an excellent record of Pleistocene glaciation which can be used to fill a significant spatial gap in published glacial chronologies.

Glacial deposits in the Trinity Alps were located using Google Earth and previously published maps, and were confirmed in the field. This study focusses on the Long Gulch and Trail Gulch Valleys at the northern margin of the Trinity Alps Wilderness Area. 24 samples from 5 moraines were taken for ¹⁰Be dating, as well as 3 samples from striated bedrock. Of the 24, 10 samples were selected for exposure age analysis: 3 from bedrock, 5 from an LGM moraine and 2 from an older moraine. These ages should provide at least 2 ages of glacial abandonment within the valleys. Our new ages will be combined with 26 ¹⁰Be ages collected between 2004-2012 to provide a detailed chronology of late Pleistocene glacial advances and retreat in the Klamath Mts. Our new ages will be combined with numerical modelling of glacial extent in Trail Gulch and Long Gulch using a coupled ice-flow model and mass and energy balance model. This will allow us to interpret the specific climate conditions for each glacial the two valleys.

Initial dating results suggest that at least 2 pulses occurred during the LGM at approximately 15 and 19 ka. When paired with the final chronology, results from the paleoclimate modelling should provide new insights into the latitudinal variation in timing and character of paleoclimate change in the western US.