HR: 0800h
AN: C41B-0475    [Abstracts]
TI: Analogue Experimental Study of Debris Entrainment by Ice Growing into Supercooled Water
AU: * Spannuth, M
EM: melissa.spannuth@yale.edu
AF: Department of Geology and Geophysics, Yale University, Kline Geology Lab PO Box 208109, New Haven, CT 06520-8109, United States
AU: Wettlaufer, J S
EM: john.wettlaufer@yale.edu
AF: Department of Geology and Geophysics, Yale University, Kline Geology Lab PO Box 208109, New Haven, CT 06520-8109, United States
AB: Field studies have identified several processes by which glaciers and ice sheets can accumulate debris-rich basal ice. Although significant effort has gone into modeling these processes and the inferred effects on glacier dynamics, there is a dearth of laboratory investigations. In particular, in several field settings debris entrainment by frazil ice growing in glaciohydraulically supercooled water channels has been suggested as the source of the dirty basal ice. However, the physical mechanisms by which frazil ice actually traps the sediment and then incorporates it into the basal ice remain unclear. In order to clarify this process, we have frozen solutions of 140 nm-diameter silica spheres dispersed in water in a 400 micron-thick cell supercooled to between -2 and -6 C. The thinness of the cell results in an essentially two-dimensional ice fabric, thus allowing us to observe the particle distribution and movement during freezing and subsequent coarsening. During the nucleation and unstable growth of the ice we find that many particles segregate to the liquid interstices between ice dendrites. Over the next 10 seconds the inter-dendrite liquid freezes and some particles become trapped between dendrites while some are pushed ahead of the ice front. As the ice coarsens over several days, particles migrate through the ice due to temperature gradient regelation and move with the grain boundaries/veins/nodes, which evolve to accommodate the coarsening. While the physical conditions in our experiment do not correspond exactly to those of subglacial conduits, our observations of the microscopic dynamics of particles during the freezing and evolution of supercooled, sediment-laden water can help guide future experiments and provide insight into the ice and sediment textures observed in glacier basal ice.
DE: 0720 Glaciers
DE: 0726 Ice sheets
DE: 0730 Ice streams
DE: 0736 Snow (1827, 1863)
DE: 0794 Instruments and techniques
SC: Cryosphere [C]
MN: 2007 Fall Meeting