POST-GLACIAL DRAINAGE DEVELOPMENT AND FLUVIAL GEOMORPHOLOGY OF THE TUG HILL PLATEAU, NEW YORK

At the Last Glacial Maximum, the Adirondack Mountains and Tug Hill Plateau of northern New York were completely covered by the Laurentide ice sheet. Abundant drumlins and other streamlined landforms across the top of Tug Hill record the direction of ice flow as it entered the Black River Valley and subsequently over Tug Hill and the Adirondacks. Bedrock channels and incipient tunnel channels cross cut these streamlined landforms suggesting complex interactions between erosion by the ice sheet and the subglacial fluvial conditions during times of decoupling between the ice sheet and the bed. As the ice receded following the LGM, proglacial lakes occupied the lowlands adjacent to the Tug Hill Plateau, setting baselevel for drainage networks developing sub-aerially in the absence of ice. The gentle southwestern dip of Tug Hill’s Paleozoic strata, and the alternation of weak shale and more resistant limestone sets another important boundary condition for both ice sheet erosion and post-glacial drainage reorganization and localized incision. This study investigates the imprint of glacial erosional processes, subglacial and ice margin fluvial processes, and lithology on the modern drainage network of Tug Hill Plateau.

For drainage basins across Tug Hill, we investigate how the dominant drainage pattern compares to the local trends of streamlined landforms vs. discontinuous tunnel and ice margin channels. Dramatic canyons, or ‘gulfs’ in the local vernacular, have incised into the eastern and western margins of the plateau. However, the magnitude of incision and the extent of how far up-system that incision has propagated vary from basin to basin. We are working to understand the origin and evolution of these gulfs, and distinguish between those that re-occupy subglacial and ice margin canyons vs. those that represent entirely post-glacial incision. High resolution (1-meter) airborne LiDAR for the Black River Valley to the east of Tug Hill allows for careful consideration of channels’ longitudinal profiles and patterns of incision across the cuesta-like eastern margin of the plateau. Previous studies’ mapping of proglacial lake levels in the Black River Valley, and new insight into what appear to be discontinuous wave-cut benches on Tug Hill guide our accounting for falling baselevel as Tug Hill’s eastern gulfs formed.