EAR-PF: Experimental study of the dynamics of frozen, cohesive river banks: bridging pore-scale properties with channel-scale dynamics.

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Dr. Kieran Dunne has been awarded an NSF EAR Postdoctoral Fellowship to study the effects of widespread thawing in the Arctic on changes in frozen riverbank erosion and on the release of greenhouse gasses and heavy metals. The work will take place under the mentorship of Dr. Michael Lamb at California Institute of Technology. Accelerating climate change in the Arctic is leading to the widespread thawing of permafrost (ice and soil that typically remains frozen throughout the year). The loss of permafrost results in weakening of riverbanks, river channel migration and speeds up the release of greenhouse gasses and heavy metals. These environmental issues combined with changes in the shape of rivers have led to the displacement of communities in the Arctic. This project seeks to characterize the ways that the composition of permafrost riverbank impacts the rate of riverbank erosion and river channel migration in the Arctic. The work includes a series of experiments to determine the properties that control erosion and river migration, contributing to a framework for improved management of river systems in polar regions and a better understanding of the global carbon cycle. The project also includes education and outreach activities that incorporate preexisting California Institute of Technology programs for high school and undergraduate students. Dr. Dunne also plans to develop and distribute online educational modules on river processes hosted on SedEdu.Huge regions of land in the Arctic through which rivers incise are comprised of permafrost. The presence of pore ice in permafrost substrates has been shown to have a profound effect on the erodibility bank material as pore ice greatly increases the yield strength of frozen soil relative to unfrozen soil. As a result, the erosion rates of permafrost soils are highly sensitive to climate-driven changes to both local hydrological and atmospheric temperature conditions. This study seeks to develop a mechanistic understanding of the effects of permafrost composition and water temperature on the erosion rate of frozen riverbanks. A suite of experiments will be performed to determine the effects of cohesive sediment on the thermomechanical and geotechnical properties of permafrost substrates that govern the rate of riverbank erosion in Arctic regions. This experimental approach will be coupled with analysis of high-resolution satellite imagery of natural, permafrost rivers in the Arctic to determine how rates of channel bank erosion and lateral migration changes throughout the year in response to the governing mechanisms explored in the lab.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.