T22 Cordilleran Ice Sheet Outburst Floods: From Glacial Lake Missoula to the Hubbard Glacier

Sunday, 22 October 2017
8:00 AM - 12:00 PM
Chelan 5

COMPARING LANDFORMS AND LANDSCAPES BETWEEN THE CHANNELED SCABLANDS AND CANADA'S WESTERN INTERIOR

Paper number: T22-10
Program: Technical Sessions
Time: 10:30 AM – 10:45 AM

Authors

  • Robert R. Young Presenting Author
    University of British Columbia Okanagan, Kelowna, BC

Abstract

Digital elevation models (DEMs) from several sources reveal large, previously unrecognized glacial landforms. Work on landforms and sediment relationships test land-forming models of individual features. Crosscutting relationships further tested the models, and revealed the sequence and type of land-forming processes. Models of individual feature formation, and as a whole landscape are tested against those discovered in the Channeled Scabland of Washington State.

Flood channel analogues in the Washington Scablands were seen, except that they rise over a height of almost 800 m and are nearly 80 km wide. In the Scablands hummocky features, including ridges and swales and potholes, originated with erosion by “kolks” within an initial broad sheet flow as they eroded into a variety of substrates, including basalt. Subsequent concentration of flow eroded channels, leaving the hummock areas as elevated remnants between the channels. Similarly, hummocky topography exists between megachannels in Alberta, which are also cut into a variety of substrates. Hummock composition includes an array of sediments and structures within a uniform hummocky topography. The hummocks are therefore also fluvial erosional remnants and not formed by glacial processes.

Other divergences with the Channeled Scabland model were found in higher elevation, subglacial fluvial forms. An upland between the megachannels, 180 m above the hummocks, and 300 m above the eastern megachannel has a tunnel channel containing eskers cut into its upper surface. The eskers are sharp crested, indicating no post-depositional deformation, but have crushed gravel, indicating extreme vertical loading within a channel. The distal end of the esker overlies the hummocky belt, indicating esker deposition occurred after hummock formation. Wider and deeper channels that go uphill are found at similar elevations approximately 300 km SW. The inference is that extreme discharges capable of achieving these elevations were regional in scale, and 300 m higher than megachannels that border the hummocks. These discharges occurred near glacial maximum, and the regional array of landforms was produced sequentially afterwards. There was no alteration by retreating glacial processes, suggesting the Laurentide Ice Sheet collapsed and melted in place.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-306888

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