Subtemperate regelation exhibits power-law premelting

Abstract

Wire regelation is a common tabletop demonstration of the pressure-dependence of the ice melting temperature where a loaded wire moves from top to bottom through a block of ice, yet leaves the block intact. With the background temperature fixed at the bulk melting point ∼0°C, the elevated ice and liquid pressures beneath the wire cause melting because of the negative Clapeyron slope, while refreezing takes place above the wire where the pressures are reduced. Regelation is a model for temperate glacier ice moving through small bedrock obstacles. Laboratory experiments demonstrate that regelation continues to occur, albeit at much slower velocities, when the fixed background ice temperature is cold enough that the wire load is insufficient to produce bulk melting, suggesting that premelting plays a central role. Here, we compile available data for wire regelation at all temperatures. We then develop a model for the subtemperate data points, where the film thickness depends on the temperature below the melting point. We find agreement between the power-law model and the laboratory data for slow regelation velocities, allowing us to characterize the dominant premelting mechanisms for different wire compositions. These results advance our understanding of the role of premelting in subtemperate glacier sliding.