Ice mélange and the rheology of floating granular materials

Between the boundaries of tidewater glaciers and the ocean sits ice mélange, the worlds largest granular material. Created by glacial calving events in narrow straits or fjords, the dynamics and physical properties of ice mélange are important for determining variability in calving rates and meltwater release. We explore ice mélange with experiments that study its rheology, transverse velocity profile, and thickness profile. Polypropylene is used as a substitute for comminuted ice, due to their similar densities. We explored a variety of shapes in a narrow water tank with rough walls to simulate a fjord. A suspended acrylic plate acts as our glacier terminus. It is attached to two force sensors, allowing us to measure the force imparted by the mélange. Cameras mounted above and on the side of the chamber allow us to track surface velocity fields (using PIV) and depth profiles respectively. By comparing our results to simple, depth-averaged models of granular fluids, the thickness profile provides the friction coefficient between the mélange and the walls. Additionally, velocity profiles transverse to the flow direction allow us to test the accuracy of different granular rheologies. Finally, our experimental setup allows for rapid perturbations to the mélange (i.e. calving events), whereby the transient force and recovery to equilibrium can be measured.