Late Quaternary Glacial History of the Southern Uinta Mountains – Ben Laabs

Summary
        Alpine glaciers were numerous in the Uinta Mountains during the Last Glacial Maximum, as documented by W. W. Atwood (1909), G. Osborne (1973), J. Munroe (2001), E. Carson (2003), J. Shakun (2003) and myself (Laabs and Carson, 2005, in press; click here to view maps of the Uintas and paleo-glacier extents). The objectives of my research are (1) to determine the extent and timing of late-Quaternary glacier advances and retreats on the south side of the Uinta Range; (2) the timing of the Last Glacial Maximum for the entire Uinta Range; and (3) set limits on climate during and since the last glaciation in northern Utah.  The results of my study, in collaboration with ongoing research in the Uinta Mountains (e.g., Munroe, 2003; Carson 2003), will include a paleoclimate reconstruction approximately spanning the end of the Last Glacial Maximum to historical time.  Procedures utilized in this study include surficial mapping in the field and on air photos, radiocarbon dating of alpine lake sediments, and surface-exposure dating of moraines using cosmogenic ¹⁰Be and ²⁶Al.

Fieldwork
        In summer 2002, I began mapping the surficial geology of the southern Uinta Mountains in the Ashley National Forest, working with Dr. Jeffrey Munroe (Middlebury College), Jeremy Shakun (Middlebury College, now at UMass-Amherst), and Darlene Koerner (Ashley National Forest – Vernal Ranger District).  Since this time, several students have aided in improving the resolution of this effort, particularly in the Yellowstone and Wolf Creek drainage basins. Mapping glacial deposits has also aided in reconstructing paleo-glacier ELA that compliment those done by Munroe on the north slope; these reconstructions were published by Shakun et al. (2003).
        I also began sampling quartzite boulders on moraines that formed during the Last Glacial Maximum (LGM) on the south slope to obtain cosmogenic exposure ages.  With these ages, I hope to constrain the timing of the LGM for the entire Uinta range. Analyses of in-situ ¹⁰Be in moraine boulders are completed for the Yellowstone, Lake Fork and North Fork Duchesne moraines in Laabs (2004), in addition to boulders on a moraine in the upper Provo basin where Kurt Refsnider is conducting his M.S. research. Additional analyses, including analyses of cosmogenic nuclides on moraine boulders in the northern Uintas, are underway and will be run at PRIME Lab (Purdue University).
        Other chronological control on the timing of glacial events in the Uintas is being generated from radiocarbon in lake-sediment cores retrieved from lateral moraine-dammed lakes.  Jeff Munroe is leading this research and will present a compilation of results from lakes in the southern Uintas at the GSA meeting in Salt Lake City.

Laboratory work
        Extraction of in situ cosmogenic ¹⁰Be and ²⁶Al from samples of quartzite moraine boulders is being done in the UW cosmogenic nuclide extraction laboratory, supervised by Brad Singer. We have slightly modified methods developed by Bierman et al. (1999) and Douglass et al. (2004) to accommodate specific physical and chemical properties of Uinta Mountain quartzite. Samples are being prepared into targets for AMS analyses at the PRIME Lab at Purdue University.

I am also beginning work to apply two 2-D numerical models developed by Plummer and Phillips (2003, QSR) to three formerly-glaciated valleys in the southern Uinta Mountains. The first model is used to calculate energy balance, which determines accumulation and ablation rates for cells within the valleys. The output of this model is read into the second model, an ice-flow model, which simulates glacier growth. Thus, glacier growth in the flow model is dependent on the paleoclimate parameters in the energy-balance model. The goal of this work is to determine a range of paleoclimate scenarios that may have been responsible for the glaciation during the LGM in the southern Uinta Mountains. Preliminary model results will be published soon in Laabs et al. (in press, Geomorphology).

Publications (papers, theses and abstracts)

Carson, E.S., Munroe, J.S., and Laabs, B.J.C., 2005. Radiocarbon constraints on timing of deglaciation and deposition of valley-fill sediments from Dry Gulch, Uinta Mountains, northeastern Utah: Abstracts with Programs, Geological Society of America, vol. 37, no. 7, in press.

Carson, E.S., Munroe, J.S., and Laabs, B.J.C., 2003. Post-Glacial Environmental Change in the Uinta Mountains, Utah: Proceedings of the Rocky Mountain Anthropological Conference.

Laabs, B.J.C., 2004. Late Quaternary glacial and paleoclimate history of the southern Uinta Mountains, Utah: Ph.D. Dissertation, University of Wisconsin, Madison, 162 pp.

Laabs, B.J.C. and Carson, E.C., 2005. Glacial geology of the southern Uinta Mountains, In Dehler, C.M., Pederson, J.L., Sprinkel, D.A., and Kowallis, B.J. (eds.), Uinta Mountain Geology, Utah Geological Association Publication 33, Salt Lake City, Utah, in press.

Laabs, B.J.C., Munroe, J.S., Shakun, J.D., and Caffee, M., 2005. New evidence of synchroneity between deglaciation in the Uinta Mountains and the fall of Lake Bonneville: Abstracts with Programs, Geological Society of America, vol. 37, no. 7, in press.

Laabs, B.J.C., Plummer, M.A., and Mickelson, D.M., 2005. Climate during the Last Glacial Maximum in the Wasatch and southern Uinta Mountains inferred from glacier modeling: In Munroe, J.S., Laabs, B.J.C., and Carson, E.C. (eds.), Quaternary Landscape Change and Modern Process in the Western U.S., Elsevier, Amsterdam, in press.

Munroe, J.S., Laabs, B.J.C., Pederson, J.L., and Carson, E.S., 2005. From cirques to canyon cutting: new Quaternary research in the Uinta Mountains: In, Dehler, C.M. and Pederson, J.L. (eds.), Fieldtrip Guide, 2005 Annual Meeting of the Geological Society of America, Salt Lake City, Utah, Geological Society of America, Boulder, CO, in press.

Shakun, J.D., Munroe, J.S., and Laabs, B.J.C., 2003. Last Glacial Maximum Equilibrium-Line Altitudes and Paleoclimate, Northeastern Utah: Geological Society of America, Abstracts with Programs, vol. 35, no. 6.

Other Links to Uinta Mountain Research

Quaternary Research in the Uinta Mountains (the UMRG homepage)

Jeff Munroe’s research in the Uintas

Eric Carson’s research in the Uintas

Acknowledgments
        This project is generously supported by the NSF (EAR-0345277), the Geological Society of America, the Desert Research Institute, the UW-Madison Vilas Fellowship, the Purdue Rare Isotope Measurement Laboratory (PRIME Lab), and the Ashley National Forest.

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Updated 9/5/05