GLACIAL IMPRINTS OF THE OKANOGAN LOBE, SOUTHERN MARGIN OF THE CORDILLERAN ICE SHEET: A GIS-AIDED RECONSTRUCTION

Glaciation is a fundamental control on the morphology and processes acting on, mid- to high-latitude continental margins. In northeastern Washington State (USA), the Okanogan lobe of the Cordilleran Ice Sheet flowed southward through the Okanogan trough from the Interior Plateau of British Columbia and invaded the Waterville Plateau during the late Wisconsin (Fraser Glaciation). This had a profound influence on the landscape and meltwater routing and flooding events in adjacent areas (e.g., Channeled Scablands). To help improve our understanding of the spatial distribution, morphology, processes, and dynamics of the Okanogan lobe, we have extracted glacial bedform (i.e., drumlin, macro-flutes, till lineations, and eskers) information from digital elevation models (DEMs) and aerial photographs, delineated the ice-flow pattern, and reconstructed the ice-surface profile. Our study reveals the spatial distribution and morphology of glacial features and their landscape. The arrangement of sediment-rich (soft bed) areas and exposed bedrock (hard bed) may reflect a link to the local topography and probably the ice-sheet delivery of sediments. A higher proportion of drift is found along the western and central portion of the Waterville Plateau, while progressively more bedrock is exposed to the east and generally at lower elevations. The late-glacial history in this area is more complex than previously thought; some glacial landforms overlap older forms indicating more than one ice-flow event and possibly a switch in flow/thermal regimes. Reconstructions of the ice-surface morphology and estimated driving stresses (17–26 kPa) implied from ice thickness and surface slope in the terminal area suggest fast basal flow characteristics during the last ice-flow event.