Experimental observation of the onset of fracture percolation in columnar ice

Abstract

While the contribution of brine channels to the critical behavior of sea ice permeability is well known, fractures can also contribute to the critical behavior of ice permeability. Above a critical fracture density, cracks link together to create a continuous pathway for flow. To isolate the contribution of fractures to percolation through ice, we present novel experiments to quantify the critical strain required for the onset of fracture percolation in freshwater columnar-grained ice. We monitored the percolation of the ice as it was compressed uniaxially across the columns at −10oC to axial strains of 0.5–2% at a strain rate of 10−5 s−1, i.e., 1 order of magnitude below the ductile-to-brittle transition. We observed that the threshold for along-column permeability corresponds with peak strength. Lateral connectivity develops over limited distances postpeak strength near the onset of near-steady state flow and is facilitated by the breakage of the columns.