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TILTED TREES AND LOST LAKES: DENDROGLACIOLOGICAL INSIGHTS INTO LITTLE ICE AGE GLACIER ACTIVITY IN THE NORTHEAST ST. ELIAS MOUNTAINS, YUKON TERRITORY

REYES, ALBERTO V  Department of Earth and Atmospheric Sciences, University of Alberta.
Luckman, Brian H  Department of Geography, University of Western Ontario.
Smith, Dan J  Department of Geography, University of Victoria.
Jensen, Britta J.L.  Department of Earth Sciences, Simon Fraser University.
Clague, John J  Department of Earth Sciences, Simon Fraser University.

Chronologies of regional Holocene glacier activity in the St. Elias Mountains can complement ongoing high-resolution paleoclimate investigations based on tree-ring records and high-altitude ice cores. Previous investigations of Little Ice Age (LIA) glacier activity in the northeast St. Elias Mountains, however, were limited by uncertain ecesis intervals and lichen age-growth relationships, as well as large error terms associated with calibrated radiocarbon ages at LIA time scales (Denton and Stuiver, 1966; Rampton, 1970; Denton and Karlén, 1977). Tree-ring dating of overridden trees and tilted snags, which has been extensively used in coastal Alaska (Calkin et al., 2001) and the Canadian Rocky Mountains (Luckman, 2000) to resolve LIA glacier advances at decadal timescales, has not been applied in the St. Elias Mountain because suitable dating material has not previously been located.

Here we present initial results of several investigations that are broadly targeted at elucidating the Little Ice Age behaviour of glaciers in the northeast St. Elias Mountains. Dendrochronological techniques were used to refine the history of Neoglacial Lake Alsek (Clague and Rampton, 1982), which formed at least three times since the early 17th century when Lowell Glacier blocked drainage of the south-flowing Alsek River. Crossdated driftwood associated with three phases of Lake Alsek constrains the timing of advanced positions of Lowell Glacier, including its LIA maximum position, which was probably attained in the 17th century. Similar methods are being used to develop a high-resolution chronology of ice-dammed Lake Donjek (Perchanok, 1980) which potentially threatens the Alaska Highway transportation corridor north of Kluane Lake. We dated two distinct driftwood strandlines that suggest Donjek Glacier was at its maximum LIA position in the early-mid 19th century. At Kaskawulsh Glacier, white spruce stems were sheared and tilted when terminal moraines were deposited during the culmination of its most extensive Little Ice Age advance. The ages of seven such stems, which we dated by comparing their ring-width patterns to a ~900 year tree-ring chronology from nearby south Kluane Lake, suggest that Kaskawulsh Glacier was at its most extensive Holocene position in the early-mid 18th century. Our results highlight the potential for long tree-ring records to provide decadal-scale dating of geomorphic events in the northern St. Elias Mountains.

REFERENCES
Calkin, P.E., Wiles, G.C., Barclay, D.J., 2001, Holocene coastal glaciation of Alaska: Quaternary Science Reviews, v. 20, p. 449-461.



Clague, J.J., Rampton, V.N., 1982, Neoglacial Lake Alsek: Canadian Journal of Earth Sciences, v. 19, p. 94-117.



Denton, G.H., Karlén, W., 1977, Holocene glacial and tree-line variations in the White River Valley and Skolai Pass, Alaska and Yukon Territory: Quaternary Research, v. 7, p. 63-111.



Denton, G.H., Stuiver, M., 1966, Neoglacial chronology, northeastern St. Elias Mountains, Canada: American Journal of Science, v. 264, p. 577-599.



Luckman, B.H., 2000, The Little Ice Age in the Canadian Rockies: Geomorphology, v. 32, p. 357-384.



Perchanok, M.S., 1980, History of a glacier-dammed lake on Donjek River, Yukon. MA thesis, Carleton University, Ottawa, Ontario, Canada.



Rampton, V.N., 1970, Neoglacial fluctuations of the Natazhat and Klutlan Glaciers, Yukon Territory, Canada: Canadian Journal of Earth Sciences, v. 7, p. 1236-1263.


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