EAR-PF: Revisiting Megafloods: Insights From Glacial Isostatic Adjustment on Flood Size, Flow Routes, and Climate Response

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Dr. Tamara Pico has been awarded an NSF EAR Postdoctoral Fellowship to investigate the influence of glacial isostatic adjustment on late Pleistocene catastrophic flooding to improve our understanding of the timing and routing of mega-floods. The work will be conducted at the California Institute of Technology and Oregon State University. During the last ice age, 22,000 to 14,000 years ago, dozens of catastrophic mega-floods from an ice-dammed Glacial Lake Missoula scoured the landscapes of Idaho and eastern Washington, forming what are known as the Channeled Scablands. These glacial lake outbursts are the largest known floods on Earth. Reconstructing the magnitude of these events informs our understanding of how floods shape Earth's landscapes and relate to abrupt changes in climate. Over the period of flooding, ice sheet melting caused crustal deformation with rates of about 10 mm/yr, which is orders of magnitude above regional tectonic uplift rates, resulting in a substantially different regional topography relative to today. This process of glacial isostatic adjustment has been neglected in prior estimates of flood volumes or discharge, introducing a potentially large error, which has not yet been quantified. This study will provide a more accurate estimates of total discharge during flood events which in turn will help quantify the response of the ocean and broader climate system to mega-floods. In addition, the research will help inform for outburst flood planning by studying the nature of past catastrophic flooding and the stability of ice sheets in response to climate change. The PI has extensive leadership and outreach experience in women in science and underrepresented minority groups and will continue a committed involvement in these communities. Outburst mega-floods from glacial Lake Missoula, occurring from 22,000 to 14,000 years ago, are the largest known floods on Earth. Prior estimates of water volume and flow discharge during these flood events rely on slopes based on modern topography. Over this time period, glacial isostatic adjustment caused crustal deformation with rates of about 10 mm/yr, orders of magnitude above regional uplift rates, and changed local slopes by about 30%. Thus, prior estimates of flood volumes include a potentially large error, which has not yet been quantified. Furthermore, over the interval of Missoula flooding, patterns of uplift and subsidence due to glacial isostatic adjustment evolved significantly, and this reshaping of topography may explain observed changes in flood routing over time. This proposal, within disciplines of Geomorphology and Geophysics, seeks to investigate the influence of glacial isostatic adjustment on the Channeled Scablands landscape as it developed over the course of Missoula mega-flood events. Three interconnected goals for this project are proposed: (1) reconstruct drainage path evolution across the interval of flood events in response to glacial isostatic adjustment; (2) accurately estimate flood discharge using slopes corrected for glacial isostatic adjustment; and (3) connect the response of ocean, and broader climate system, to newly-refined estimates of total freshwater flux. Glacial isostatic adjustment simulations will be performed to predict paleo-topography and paleo-slopes in the Channeled Scablands. Flood drainage pathways and flood discharge estimates will be calculated using the resulting topography corrected for glacial-isostatic adjustment. Finally, these new estimates of freshwater flux will be compared to the geochemical record of sediment cores collected off the Oregon coast, to assess the response of the ocean's biological system to mega-flood events. The proposed research, which transcends multiple scales by using glacial-isostatic adjustment modeling to connect geomorphic processes to both small and large wavelength features of the mantle's response to ice loading, ultimately linking local short-lived outburst flooding to longer global climate changes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.