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Abstract Within the temperate ice of ice stream shear margins, high strain and accompanying recrystallization likely result in longitudinal foliation characterized by thin, steeply dipping ice layers with distinct variations in grain size and bubble content. The sensitivity of ice permeability to these factors, particularly grain size, implies that foliation causes shear‐margin ice to be hydraulically anisotropic. In this study, the permeability of foliated ice is measured in disks cut from cores from Athabasca Glacier, allowing permeability anisotropy to be assessed. We collected cores oriented normal and parallel to foliation from beneath the weathered crust of the glacier. Permeability values range from approximately  m²and correlate with the textures and orientations of foliation layers. Results indicate that the anisotropic permeability of foliated ice can be approximated using a model that incorporates an empirical grain‐size/permeability relationship and a model of vein clogging by air bubbles. For water flow parallel to foliation, the arithmetic mean of the area‐weighted permeability closely approximates the bulk permeability; for flow perpendicular to foliation, measurements agree with the harmonic mean permeability, weighted to the thickness of each layer. These findings imply hydraulic anisotropy spanning several orders of magnitude in temperate glacier ice, with water flux governed by the most and least permeable layers in the flow‐parallel and flow‐perpendicular cases, respectively. 

Abstract To better constrain meltwater transport and ice viscosity in temperate glaciers, particularly in ice stream shear margins, we use a custom permeameter to study the untested model relationship between the permeability of temperate ice and its liquid water content. The permeability of lab-made ice of two mean grain diameters (1.8 and 4.2 mm) is measured, and water content is controlled with the ice salinity and measured calorimetrically. Fluorescein dye is added to through-flowing, chilled water to highlight flow pathways through the ice after experiments. As predicted by a simple model, permeability increases with approximately the square of the water content and by about three orders of magnitude across water contents of 0.1–4.4%. However, permeability values are less than those of the model by average factors of 2.6 and 4.1 for the finer and coarser ice, respectively. This discrepancy is likely due to tortuous, truncated or air-clogged veins. The order-of-magnitude agreement between measured and modeled values may indicate that reduced permeability from these factors is nearly compensated by preferential flow in oversized veins that are isolated or arborescent. Both kinds of preferred flow pathways are observed but the latter only in fine-grained ice at water contents > 2%.