Laboratory Studies of the Physics of Debris Entrainment, Transport, and Deposition at the Bed of a Temperate Glacier

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Processes of erosion, entrainment, and deposition at the beds of glaciers govern the supply of debris available for subglacial modification, and thus, play an important role in the evolution of subglacially sculpted topography. In addition, deformation of subglacial debris directly influences the dynamics of many glaciers and ice sheets. Despite the strong motivation for studying the physics of interactions between concentrated debris, ice, and glacier beds, no laboratory experiments under well controlled, realistic conditions have been conducted. We propose a series of experiments in which conditions at the bed of a temperature glacier will be closely simulated. In some experiments, a rock bed slid beneath a fixed block of temperate ice that contains dense arrays of rock particles. Our goals will be to simulate glacial abrasion and debris comminution, and to demonstrate the conditions under which basal melt-out and entrainment of debris occur. Experiments to date indicate that these processes are strongly affected by the tendency for ice to penetrate and flow through debris by regelation. To better understand this process regelation of ice through till will be idealized in other experiments by pushing ice through a three-dimensional array of spheres. Results will be compared with predictions of an existing regelation theory, which we will modify by including the important effect of solutes on thermal gradients. In both series of experiments, all pertinent glaciological variables will be monitored, including ice and bed temperature, basal melt rate, and effective pressure. These experiments will held fill a conspicuous void in the study of glacial geologic processes.