Pre-Late Wisconsin Outburst Floods and Their Pathways

Kate Farrington

Whitman College, Walla Walla WA 99362

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Study of newly discovered sites containing pre-late Wisconsin outburst flood-related deposits has led to improved understanding of possible flood provenance. The three sites in this study contain reworked, caliche capped flood deposits containing exotic clasts of both granitic and metasedimentary lithologies. These clasts, in addition to a micaceous sediment matrix, support three main provenance hypotheses. Based on the lithologies of transported clasts as compared to the local rocks of different surrounding areas, the most likely origins for the floodwaters are Lake Columbia, an older Lake Missoula, or from melting and release of water from under the Cordilleran Ice Sheet in southern British Columbia.