GSA Connects 2021 in Portland, Oregon

Paper No. 147-10
Presentation Time: 10:50 AM


PICO, Tamara1, LAMB, Michael P.2, DAVID, Scott3, LARSEN, Isaac3, MIX, Alan4 and LEHNIGK, Karin E.5, (1)CaltechGeological & Planetary Sciences, 20 Oxford St, Cambridge, MA 02138-2902, (2)Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, (3)Department of Geosciences, University of Massachusetts Amherst, Amherst, MA 01003, (4)College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, 104 CEOAS Admin Bldg, Corvallis, OR 97331, (5)Geoscience, UMass Amherst, 611 North Pleasant Street, 233 Morrill Science Center, Amherst, MA 01003

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.