HR: 1340h
AN: U43A-0827    [Abstracts]
TI: New Evidence for Holocene Glacier Fluctuations on Mt. Baker, Washington
AU: Davis, P T
EM: pdavis@bentley.edu
AF: Department of Natural Sciences, Bentley College, 175 Forest Street, Waltham, MA 20452-4750 United States
AU: * Osborn, G
U43A-0827 AF: Geology and Geophysics, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4 Canada
AU: Menounos, B
U43A-0827 AF: Geography, University of Northern British Columbia, 3333 University Way, Prince George, BC V2N 4Z9 Canada
AU: Ryane, C
U43A-0827 AF: Geology and Geophysics, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4 Canada
AU: Clague, J
U43A-0827 AF: Department of Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6 Canada
AU: Riedel, J
U43A-0827 AF: Department of Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6 Canada
AU: Koch, J
U43A-0827 AF: Department of Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6 Canada
AU: Scott, K
U43A-0827 AF: Cascades Volcano Observatory, U.S. Geological Survey, 1300 SE Cardinal Court, Bldg. 10, Suite 100, Vancouver, WA 98683 United States
AB: Ongoing research on Mt. Baker, an active Cascades stratovolcano, provides new constraints on the timing of Holocene glacier fluctuations. Previously mapped deposits on the southwest flank of Mt. Baker suggested to some that glacial advances during the early to mid- Holocene were more extensive than those during the Little Ice Age (LIA). This interpretation was based on the presence and absence of Mazama (ca. 6800 ¹⁴C yr BP) and Mt. Baker set OP (ca. 5800 ¹⁴C yr BP) tephras, and a scoria deposited at ca. 8,800 ¹⁴C yr BP. Our work indicates a more complex distribution of the scoria than previously thought, as well as its presence on deposits reported to be scoria-free. In addition, many of the landforms previously mapped as moraines are bedrock or bedrock-cored ridges. At Easton Glacier, we identified two tills separated by an abrupt unconformity in the east lateral moraine about 20 m below the moraine crest. The unconformity is marked by (1) a deformed mat of peat and detrital wood fragments and trunks up to 0.5 m in diameter, (2) two tephra layers, and (3) a thick red silt below the two tephra layers that may be a weathering product of the tephra(s) or, alternatively, a third, weathered tephra. The two tephras have field characteristics identical to those of Mazama and Baker Set OP present on the south flank of the volcano. Two samples of detrital wood yielded ages of 5260 ± 70 and 5240 ± 70 ¹⁴C yr BP, which we interpret to indicate (1) construction of a moraine prior to 6800 ¹⁴C yr by a glacier with an extent similar to that of the LIA, (2) retreat of the glacier, stabilization of the moraine, and establishment of a forest, and (3) advance of the glacier at ca. 5200 ¹⁴C yr, overriding the vegetated moraine surface. This advance is correlative with the well-known `Garibaldi Advance' in the southern Coast Mountains of British Columbia. At Coleman Glacier, an unconformity about 12 m below the crest of the southwest lateral moraine is marked by a laterally-continuous wood mat. The wood mat dips into the proximal flank of the moraine and contains logs up to 0.4 m diameter, one of which dates to 940 ± 50 ¹⁴C yr BP. This age is consistent with radiocarbon-dated glacier advances in the Canadian Rocky and Coast mountains. The data collectively suggest that Mt. Baker glaciers responded to Holocene climate change in a similar manner to other glaciers in western North America. We have found no evidence to support the suggestion that glaciers on Mt. Baker were more extensive during the early and middle Holocene than during the LIA.
DE: 0720 Glaciers
DE: 1105 Quaternary geochronology
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Union [U]
MN: Fall Meeting 2005