Geomorphology of Glacial Lake Invermere, upper Columbia River Valley, British Columbia
Date
1991
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Abstract
In the upper Columbia and Kootenay River valleys of the Rocky Mountain Trench, between Skookumchuck and Donald, B.C., terraces of thick lacustrine silts and deltaic gravel flank parts of the valley floor. These surficial deposits indicate the presence of a former, Late Pleistocene post-glacial lake, named Glacial Lake Invermere. Lake Invermere was a long and narrow water body, which at its maximum extent occupied the Rocky Mountain Trench from Bluewater Creek, 6 km north of Donald, B.C., to an area 7 km north of Skookumchuck, B.C., a length of 210 km, with an average width of 2.5 km. The maximum area of the lake was approximately 530 km2, with an average depth of 100 m. Blockage of the lake at the northern end of the Trench is interpreted to have been the retreating glacial ice, at the south end blockage resulted from a valley-fill, in a narrow section of the Trench. Although datable organic matter, which could provide an approximate age of Lake Invermere, was not found within the study area, three published radiocarbon dates from nearby were considered to approximate the age of the lake. From the north end of the study area a 10,000 B.P. date and two dates 75 km southeast of the immediate study area at 11,900 and 12,200 B.P., suggest an approximate age of Glacial Lake Invermere at 11,500 to 10,000 B.P. Based on the measured elevations of remnant delta surfaces, Glacial Lake Invermere had two distinct phases. An initial, high phase of 900 m (A.S.L.), which was followed by a lower phase of 840 m. Final deterioration of Trench ice marked the termination of Lake Invermere, however, only after the valley-fill had been completely breached. With the disappearance of the Trench ice, the flow of water, which to this point had been in a southerly direction, reversed flow to a northerly direction, similar to that at present. A major anomaly within the study area, which provided the most significant information of the thesis, was the upper Dutch Creek fan-delta. Dutch Creek is a tributary to the Trench in the vicinity of the upper Columbia River valley, 4 km west of Fairmont Hot Springs, B.C. Originating in the Purcell Mountains, which border the west side of the Trench, Dutch Creek presently flows into Columbia Lake, the head of the Columbia River. The post-glacial creek incised into a thick deltaic and fan sequence exposing a 100 m high by 1 km long cliff face. Stratigraphic interpretation of the vertical profile indicates five major facies; basal bottomset (deltaic), foreset (deltaic), and topset beds, and horizontally stratified fan gravel mantled with a diamicton (till). The deltaic deposits within the vertical profile are interpreted to be the distal facies of a fan-foreset-type delta, which prograded into an interstadial glacial lake. The horizontally stratified gravels, interpreted as alluvial fan deposits, which overlie the deltaic sediments, are representative of a high energy pre-glacial paraglacial event. The alluvial fan gravels, perhaps in a frozen condition, are hypothesized to have provided the protective "cap" preventing gravel removal by the Trench glacier. The uppermost facies is characterized by unstratified and unsorted diamicton interpreted as glacial lodgement till. The till deposits, molded and aligned as surf ace flutings, coupled with evenly distributed fractures within clasts of the stratified fan gravel infer that the delta was overridden by ice of the final Pleistocene glaciation, providing evidence suggesting the upper Dutch Creek delta is of Middle Wisconsinan age. Based on c14 dates of 23,770 and 35,970 B.P., the upper Dutch Creek fluvial deltaic sequence was deposited during a Middle Wisconsinan interstadial period. The significance of this deposit is the fact that glacial ice did not rework the sediments, even though they form a topographic bulge on the side of the valley and were overridden by 1500 m of ice. As a result, this suggests the possibility that many other near surface deposits throughout the interior of B.C. may not necessarily be Late Wisconsinan in age, but interstadial or interglacial in age.
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Bibliography: p. 109-118.
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Citation
Sawicki, O. (1991). Geomorphology of Glacial Lake Invermere, upper Columbia River Valley, British Columbia (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/20629