Enlargement Of Englacial Conduits In Cold Ice – Verification Of Basic Theory Against Simple Experiments, And Some New Insights
Nossokoff, Austin 1 ; Rajaram, Harihar 2
2 Presenting Author
1 CU Boulder
2 CU Boulder
The dynamics of the englacial cryo-hydrologic system control two important mechanisms contributing to accelerated ice flow on the Greenland Ice Sheet- delivery of water to the bed to drive basal sliding, and cryo-hydrologic warming. The dynamics of englacial conduits in cold ice is influenced by refreezing, creep closure, and melt-driven enlargement resulting from viscous and turbulent energy dissipation (head loss) in flowing water. We report results from simple laboratory experiments focused on determining the critical flow rate through englacial conduits for producing enlargement (i.e. sufficient thermal energy generated from head loss). Our experiments did not incorporate the influence of creep closure. However, the competition between refreezing and melt enlargement was investigated. Theoretical and computational formulations of the thermodynamics were also developed. At low flow rates or with stagnant water, refreezing dominates. Warming of the ice surrounding the conduit by latent heat release was measured during the experiments and found to be consistent with theoretical expectations. At high flow rates, conduit growth was observed. Perhaps the most interesting finding from our experiments is that to explain the behavior in the high flow rate regime, an unusually high friction factor must be invoked for the conduits, because of the scalloping that naturally develops, leading to increased roughness as the conduit is enlarged. This feature is consistent with observed features of englacial and subglacial conduits, and is remarkably well reproduced even in small-scale laboratory experiments.