CGRG Bibliography of Canadian Geomorphology
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Author : Barnes, S.
Date : 2000.
Title : The paleogeography of Glacial Lake Champagne, Southern Yukon: Implications for the last deglaciation.
Publication : 30th International Arctic Workshop, Program and Abstracts, 2000. Institute of Arctic and Alpine Research, University of Colorado at Boulder
Issue :
Page(s) : 17-19.
Abstract
Glacial Lake Champagne (GLC) was a major deglacial feature of southern Yukon covering parts of the Alsek River and the Yukon River drainages. At its highest stand, GLC covered 2425 km2, had a long axis of 260 km, and a maximum depth of at least 159 m. The lake was centred over Whitehorse, extending west to near Haines Junction, east to Jake's Corner, south to near the White Pass, and north to Lake Laberge (Fig 1). There has been abundant geomorphic activity since deglaciation that has obscured the record of GLC. Poor preservation of landforms and sediments is a result of aeolian deflation, permafrost, slumping, and fluvial processes. Exposures of GLC sediments are commonly truncated at the bottom by slump deposits and at the top by loess deposits. There were no sections that had an entire succession of sediment that was interpreted to span the history of GLC. In spite of this, a paleogeographic reconstruction of GLC can be made as described below. Deltas at Lime Creek, Watson River, Takhini, and Champagne (Fig. 1) provide the best evidence for lake stage. Lime Creek Delta (LCD) and Watson River Delta (WRD) are comprised of two levels, whereas Takhini Delta (TD) is comprised of two well and one weakly developed level. The Champagne Delta (CD) has only one level. These four deltas constrain the elevation of GLC with two significant stages at 765 m and 725 m, with a minor stage at about 720 m asl. Numerous paleo-shorelines exist throughout the GLC basin. There are groups of shorelines on the north slope of the Dezadeash River valley, as well as in the Carcross region. Shorelines that lie above 765 m in the western portion of GLC are ascribed to an earlier deglacial lake that did not intrude into the Yukon River drainage. Because paleo-shorelines are discontinuous reconstructions of local isostatic response are not possible. Glaciolacustrine sediment is common in most of the modern river valleys in the region. Holocene fluvial downcutting has been significant, especially in the Yukon and Takhini River valleys, where up to 60 m of sediment have been exposed. Detailed stratigraphic logs were completed at six sites in the eastern portion of the GLC basin. The stratigraphic record is highly variable from site to site, with sedimentary successions ranging from massive silts to diamicton. The sedimentology and distribution of deposits is interpreted to be largely a function of ice proximity. The thickest exposures of glaciolacustrine sediments occur in the northeastern portion of the basin, which has the fewest examples of shorelines and deltas. The paleogeography of GLC is important as it can be used to delineate the position of ice fronts during deglaciation. There are two possible outlets for GLC, both of which must be blocked in order for the lake to exist. The Alsek River outlets were blocked by ice from the St. Elias piedmont lobe complex (Jackson et al., 1991; Duk-Rodkin, 1999). Based on the distribution of sediments and landforms associated with GLC, the Yukon River outlet was blocked north of Whitehorse at or near present day Lake Laberge. The interpretation of dominant ice flow direction was downslope (south to north) through the Yukon River valley with ice sourced in the Coast Mountains (Duk-Rodkin, 1999). This interpretation is inconsistent with the presence of an ice dam at Lake Laberge (LL) north of Whitehorse. Stagnant ice at LL is rejected as the blockage mechanism because there are (at least) two stages of GLC that were stable enough to form delta and paleo-shoreline features. Also, a stagnant ice blockage must have remained competent while ice retreated southward from the dam a distance of 100 km. It is hypothesized that ice responsible for the LL dam was part of the Cassiar Lobe, sourced east of LL in the adjacent highlands, or was part of the Cordilleran Lobe, and spilled over from the Teslin Valley. This ice blockage was active throughout the duration of the stable phases of GLC, leading to at least two stable stages, and geomorphic features consistent with a longer lived GLC.
Bibliography of Canadian Geomorphology