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Master of Science (MS)
Clark, Douglas H., 1961-
Mitchell, Robert J. (Geologist)
Amos, Colin B.
An ongoing study attempting to date boulders from Neoglacial moraines across the Sierra Nevada mountain range, CA using high precision cosmogenic radionuclide (CRN) exposure dating has yielded ages that contradict historical records and prior research in the range. To test whether these CRN ages have glacial significance or are merely a function of geomorphic processes that promote inheritance, I collected glaciolacustrine sediment cores to document independent glacier chronologies for the Lyell and Maclure glaciers in Yosemite National Park and the Price glaciers in the Desolation Wilderness. The Lyell glaciolacustrine cores indicate glacial advances from ~1830-1230 cal yr BP and ~610-80 cal yr BP. The Maclure sediment cores indicate advances from ~1650-1280 cal yr BP and ~1020-370 cal yr BP. No rock flour record is apparent from the Price sediment cores.
Based on historical accounts, prior research, and glaciolacustrine records, I interpret CRN dating for the Lyell moraines represents true age of the glacier maximum. I propose that the disparate CRN ages from the Maclure glacier result from an ice-cored moraine, which can preserve exposure histories of prior glacial advances by moraine reincorporation rather than obliteration. The Price CRN ages do not represent glacial maxima and appear to be the result of inheritance due to rockfall events, insufficient glacial erosion, and reworked rocky debris from prior deposits. From these records, I suggest that larger glaciers with an ice-free core are better suited for this new, highly precise CRN exposure dating than smaller glaciers, or those with extensive ice-cored moraines.
Western Washington University
Sierra Nevada (Calif. and Nev.)
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Cary, William, "Testing ¹⁰Be Exposure Dating of Holocene Cirque Moraines using Glaciolacustrine Sediments in the Sierra Nevada, California" (2018). WWU Graduate School Collection. 695.