Multi-scale models of thermo-mechanical feedbacks on a soft, wet bed

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Sea level is observed to be rising at an accelerating rate. A significant portion of this rise is derived from glaciers. Glacier sliding speeds and the discharge rates of the ice streams and outlet glaciers that drain Earth?s major ice sheets are primarily controlled by conditions at their beds. This project will use models to explore constraints on the bed conditions that control sliding. This will begin at small scales where the physics are understood from experiments and the results will be used to rigorously account for the effects of heterogeneities across the larger scales of observed glacier flow and associated landscape development.The project will improve glacier modeling and, ultimately, contribute to improved scenarios of future sea level rise. It will contribute to STEM workforce development by providing support for the training of a post-doctoral associate. Five undergraduate students will be entrained effectively into the research program. Outreach to middle schools will be achieved through the PI?s participation in summer teacher workshops, followed by co-development and co-teaching of a project on glaciers and sea level rise. This will include the development of a hands-on demonstration.The principal investigator proposes to develop a hierarchy of models aimed at exploring the consequences of thermo-mechanical coupling between ice, water, and till. His studies will span a very wide range of time scales: from the elastic response to tidal forcing at transiently locked portions of the bed, to the decadal periods over which significant topographic modifications take place. He will also examine a broad range of length scales, including the transitional regions accessed by seepage flows between conduits, and basin-wide responses to modeled and observed topographic roughness. Water pressures close to flotation reduce the resistance to frictional sliding and bring the effective stress supported by sediment particle contacts to within the range typical of the upper few meters of soil in subaerial environments. Long-established, experimentally supported thermo-mechanical treatments of ice-water-sediment interactions under such conditions have only recently been applied to the subglacial environment. Further work is needed to fully integrate this understanding and its implications for glacier sliding and landscape development. This proposal targets a selection of model problems aimed at elucidating the thermo-mechanical constraints on behavior near transitions in basal properties, rigorously accounting for the effects of heterogeneities across the range of scales relevant to modern observations. With the intuition gained from focused studies on carefully selected systems, the principal investigator will develop strategies for parameterizing the model predictions so that they can be incorporated in large-scale simulations of glacier and ice sheet dynamics.