Browsing by Author "Miller, Lynn A."

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    A Paleogeographic reconstruction of glacial Lakes Elk and Wigwam, southeastern British Columbia
    (1991) Miller, Lynn A.; Smith, Derald G.
    Glacial Lake Elk was one of many lakes trapped in tributary valleys of the Rocky Mountain Trench (southeastern British Columbia) during deglaciation of the southern Canadian Cordillera. Remnant features of the lake include benches of lacustrine sediment, deltas, and outlet spillway channels. Some of the deltas are anomalously large, which is attributed to the incorporation or modification of kame deposits. Glacial lakes in the Bull and White River valleys to the northwest, also blocked by Trench ice, contributed flow to the glacial Lake Elk system by draining over low divides. The Hartley Creek delta near Fernie was deposited by flow from glacial Lake Bull. Glacial Lakes Elk and Wigwam were connected at Morrissey Pass, and initially drained eastward through the Crowsnest Pass into Alberta. A plug composed of a sedimentary valley-fill west of Alexander Creek was the controlling outlet at 1371 m a.s.l.. Terraces in the fill represent paleochannel elevations as the blockage was incised. Terraces in the Hartley Creek delta and in Summit Valley, and strandlines on the Crossing Creek delta north of Elkford indicate glacial Lake Elk lowered progressively to its second outlet, Morrissey Pass (Bean/ lower Lodgepole Creeks). The Morrissey Pass outlet (1191 m a.s.l.) was established when recession of ice in the Trench allowed glacial Lake Wigwam to drain westward, providing a lower outlet than the Crowsnest Pass (1371 m a.s.1.). The Crowsnest outlet was abandoned, and glacial Lake Elk discharged southward into the lower Wigwam Valley, via Morrissey Pass, Bean, and Lodgepole Creeks. The duration of the Morrissey Pass phase of glacial Lake Elk is unknown, but incision of the outlet is represented by corresponding terrace elevations in the Hartley Creek delta Catastrophic flows eroded a third outlet of glacial Lake Elk, as a series of jokulhlaups burst through a bedrock gorge (Elko Gorge; 1014 m a.sl.) into glacial Lake Wigwam in the lower Wigwam Valley. Flood deposits include a fan-foreset delta composed of angular blocks and boulders, deposited in a low stage of glacial Lake Wigwam (1075 m a.s.L). The influx of water into the Wigwam basin likely enlarged drainage tunnels or ice marginal channels in the Trench ice dam, and the level of glacial Lake Wigwam dropped a further 75 m. A later flood incised the fan-foreset delta and deposited an extensive boulder gravel fan at 1000 m a.s.L. The floods were recorded in glacial Lake Wigwam as massive sand and gravel beds, typically displaying a coarsening upward trend followed by a fining upward trend, and capped with a silt and lastly, a clay layer. The deposits resemble the slackwater deposits of the glacial Lake Missoula floods in structure, with erosional basal contacts, incorporation of rip-up clasts, and clayey laustrine beds between flood beds. Seven rhythmic flood beds were counted, representing two major and possibly five minor seasonal flooding events, in the span of perhaps seven years. The extensive boulder gravel fan dammed the Wigwam River, and a smaller, postflood lake formed upstream. The lake existed for at least 5,370 years, based on radiocarbon dates of wood samples found in deltaic and lacustrine sediments. Five radiocarbon dates (A: 10, 490; B: 10, 450; C: 9, 930; D: 6, 950, and E: 5, 120 B.P.) and a tephra layer (interpreted as Mazama; 6, 800 B.P.) provide extensive chronological control on the post-flood Wigwam Valley deposits. A large fan-foreset delta deposited into the lake by the Wigwam River and Lodgepole Creek, and lacustrine deposits immediately downstream provide a continuous sedimentary and paleobotanical record of the period between 10, 500 and 5, 000 B.P ., and deserve further investigation.