Jerome-Etienne Lesemann, Department of Earth Science, Vancouver Island University, presents “Blame Canada (partly)! Proglacial and subglacial melwater sources from the southern margin of the Cordilleran Ice Sheet, and its contribution to erosion of the Channeled Scabland”
This presentation revisits one of J Harlen Bretz’s early notions about meltwater source(s) for the genesis of the Channeled Scabland: did some of the Channeled Scabland-forming water originate from the numerous valleys draining the southern margin of the Cordilleran Ice Sheet in southern British Columbia and northern Washington State?
With a focus on Okanogan Valley (and its northern extent into British Columbia), this presentation examines the hydrology of the Cordilleran Ice Sheet (CIS) through an assessment of evidence suggesting that large volumes of glacial meltwater were stored in lakes formed beneath and in front of the CIS at various times during its existence. Sudden drainage of some of these lakes carved large bedrock canyons and created extensive sedimentary deposits along the valley. Some of these lake drainages may have contributed to formation of the Channeled Scabland by providing additional water to some of the catastrophic outbursts of Glacial Lake Missoula. Some ongoing work on Omak and Waterville Plateaus illustrates this possibility. On these plateaus, coulees and streamlined bedrock residuals create subglacial scabland topography that is identical to the scabland topography found beyond the glacial margin in the Channeled Scabland. This form analogy implies process analogy: water erosion. The key difference is that flows over Omak and Waterville plateaus were subglacial. These coulees and residual bedrock ridges can be mapped into a regional network of anabranched channels that culminate with focused flows into Moses Coulee, suggesting that this classic Scabland landform may partially owe its origin to subglacial meltwater drainage.
Within the broader context of glacial hydrology, it will be shown that these various proglacial and subglacial drainages are entirely consistent with cycles of growth and decay of ice sheets, and are supported by a growing body of modeling and observations from modern glacial environments. The ultimate goal of this presentation is to recast the starting question from: did meltwater originate from northern sources? to how could meltwater not originate from these sources?
Thursday, November 30, 2017, 7:00 pm in CWU’s Science II Building room 103
Lecture sponsored by the Ellensburg Chapter of the Ice Age Floods Institute & CWU Geological Sciences