THE INFLUENCE OF GLACIAL ISOSTATIC ADJUSTMENT ON CHANNELED SCABLAND INCISION (Invited Presentation)

During the last deglaciation, dozens of glacial outburst floods scoured the Channeled Scabland landscape of eastern Washington, USA. Over this same period, deformation of the Earth’s crust in response to melting ice sheets changed the topography by hundreds of meters. We investigated whether glacial isostatic adjustment affected routing of the Missoula floods and incision of the Channeled Scabland. We used modern topography corrected for glacial isostatic adjustment as an input to flood models that solved the depth-averaged shallow water equations, and compared the results to erosion constraints. Our results showed that floods traversed and eroded parts of two major tracts of the Channeled Scabland—Telford-Crab Creek and Cheney-Palouse—near 18 ka, whereas glacial isostatic adjustment limited flow into the Cheney-Palouse tract at 15.5 ka. Partitioning of flow between tracts was governed by dynamic tilting of the landscape which affected the filling and overspill of glacial Lake Columbia, directly upstream of the tracts. These results highlight the impact of glacial isostatic adjustment on megaflood routing and landscape evolution.