HR: 0800h
AN: GC41A-0096    [Abstracts]
TI: New stratigraphic constraints on Holocene glacier advances at Mt. Baker, Washington
AU: * Clark, D
EM: doug.clark@wwu.edu
AF: Geology, Western Washington Univ., 516 High St., Bellingham, WA 98225-9080, United States
AU: Ryane, C
EM: cryane@ucalgary.ca
AF: Geoscience, Univ. of Calgary, 2500 University Drive NW, Calgary, AB T2N1N4, Canada
AU: Tucker, D
EM: tuckerd@openaccess.org
AF: Geoscience, Univ. of Calgary, 2500 University Drive NW, Calgary, AB T2N1N4, Canada
AU: Davis, T
EM: pdavis@bentley.edu
AF: Natural Sciences, Bentley College, 175 Forest Street, Waltham, MA 02452, United States
AU: Bowerman, N
EM: nicole_bowerman@nps.gov
AF: North Cascades National Park, Hwy 20, Marblemount, WA 98267, United States
AU: Osborn, G
EM: osborn@ucalgary.ca
AF: Geology, Western Washington Univ., 516 High St., Bellingham, WA 98225-9080, United States
AU: Clague, J
EM: jclague@sfu.ca
AF: Earth Sciences, Simon Fraser Univ., 8888 University Drive, Burnaby, BC V5A1S6, Canada
AU: Menounos, B
EM: menounos@unbc.ca
AF: Geography, Univ. of Northern British Columbia, 3333 University Way, Prince George, BC V2N4Z9, Canada
AU: Scott, K
EM: kscott@usgs.gov
AF: Cascades Volcano Observatory, 1300 SE Cardinal Court, Vancouver, WA 98683, United States
AU: Guilderson, T
EM: guilderson_23@hotmail.com
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550, United States
AU: Riedel, J
EM: jon_riedel@nps.gov
AF: North Cascades National Park, Hwy 20, Marblemount, WA 98267, United States
AU: Steig, E
EM: steig@u.washington.edu
AF: University of Washington, Department of Earth and Space Science, Seattle, WA 98195, United States
AB: New data from a lake sediment core and moraine exposures at Mt. Baker, WA, indicate that a purported early Holocene glacier advance occurred earlier, likely at the end of the Pleistocene. Previous workers used 14C ages associated with small cirque moraines on the SW flank of Mt. Baker, along with the apparent absence of a distinctive scoria (set SC; 8850 14C yr BP, ~9900 cal yr BP) from other moraines on Mt. Baker, as evidence for an advance at ~8400 14C yr BP (~9450 cal yr BP). Such an advance is important to test because it would contrast with glacial records throughout most of the rest of western North America. A 1.2-m sediment core collected from Pocket Lake, which is dammed by one of the previously dated cirque moraines, contains three tephras: Baker set BA (~5800 14C yr BP; 6600 cal yr BP), Mazama ash (6800 14C yr BP; 7600 cal yr BP), and a basal set of ash beds that are tentatively identified as Baker set SC. The lowest macrofossil in the core, ~2 cm above the top of the basal ash beds, yielded an age of 7640 ± 50 14C yr BP (~8400 cal yr BP), consistent with the tephra being SC. Initial geochemical analyses of the tephra also support this identification. These findings indicate that the previous age on the cirque moraine, from organics near the surface of the till, provides a minimum rather than a direct age for the advance that formed the moraine. A 14C age of 11,400 ± 110 14C yr BP (~13,300 cal yr BP) on bulk sediments below the basal ash is likely contaminated and therefore too old. Tephra overlying other ridges at Mt. Baker that were previously identified as post-SC, early-Holocene moraines has been identified as set SC. The ridges thus are actually pre-SC rather than post-SC in age; they may not be moraines in any event. Meanwhile, abundant 14C ages on tills below Deming Glacier indicate both Younger Dryas and Neoglacial advances, but no early Holocene advances. Together, these observations indicate that glaciers in the Mt. Baker area advanced during the YD, were of minimal extent during the early Holocene, and readvanced during the Neoglacial. The similarity of glacier fluctuations here to those in British Columbia and elsewhere in the North Cascades suggests a coherent history of Holocene climate change over a broad area of the northern Cordillera.
UR: http://mbvo.wwu.edu/index.shtml
DE: 0720 Glaciers
DE: 1105 Quaternary geochronology
DE: 1145 Tephrochronology (8455)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting