A permeameter for temperate ice: first results on permeability sensitivity to grain size

Abstract

Results of ice-stream models that treat temperate ice deformation as a two-phase flow are sensitive to the ice permeability. We have constructed and begun using a custom, falling-head permeameter for measuring the permeability of temperate, polycrystalline ice. Chilled water is passed through an ice disk that is kept at the pressure-melting temperature while the rate of head decrease indicates the permeability. Fluorescein dye in the water allows water-vein geometry to be studied using fluorescence microscopy. Water flow over durations of seconds to hours is Darcian, and for grain diameter d increasing from 1.7 to 8.9 mm, average permeability decreases from 2 × 10−12 to 4 × 10−15 m2. In tests with dye on fine (d = 2 mm) and coarse (d = 7 mm) ice, average area-weighted vein radii are nearly equal, 41 and 34 μm, respectively. These average radii, if included in a theory slightly modified from Nye and Frank (1973), yield permeability values within a factor of 2.0 of best-fit values based on regression of the data. Permeability values depend on d−3.4, rather than d−2 as predicted by models if vein radii are considered independent of d. In future experiments, the dependence of permeability on liquid water content will be measured.

Diffuse debris entrainment in glacier, lab and model environments

“…Mader, 1992 a ) yield . For comparison, in detailed observations on ice from 7–60 m depth beneath the surface of Blue Glacier, Raymond and Harrison (1975) found that average vein cross-sectional areas measured within an hour of sample recovery implied R v 0 values near 100 μ m; enhanced solute concentrations in basal ice would be consistent with larger values and accordingly we assign a nominal R v 0 = 300 μ m, which is similar to the vein sizes measured in the ice permeability study by Fowler and Iverson (2022). Guidance in estimating the permeability scale k 0 comes from theoretical considerations for polycrystalline intergranular flow described by Frank (1968) suggesting that , with the constant χ ≈ 2000 according to Nye and Frank (1973).…”

“…Ongoing experimental efforts to measure the permeability of polycrystalline glacier ice (e.g. Fowler and Iverson, 2022) are expected to reduce the uncertainty in assigning values for this important parameter. Relatively straightforward model extensions could be made to include the dependence of particle drag on vein size, though it should be noted that detailed observations of particle settling in capillary tubes (e.g.…”

Complex motion of Greenland Ice Sheet outlet glaciers with basal temperate ice

“…These results emphasize not only the importance of temperate ice but also the paucity of information regarding temperate ice at micro- and macroscales, particularly for the GrIS. Recent laboratory studies on temperate ice are limited [e.g., ( 34 , 42 )], and the parameter space for temperate ice flow is relatively unconstrained [e.g., ( 18 , 34 , 35 , 43 )], with temperate ice modeling studies mainly directed toward Antarctic shear margins. Although we do not include anisotropy, the rheology of temperate ice in our model is at the most viscous end of plausible values (see Materials and Methods), with less viscous formulations having the potential to further increase the deformation accommodated within the temperate layer.…”

Subtemperate regelation exhibits power-law premelting

“…Rempel & Meyer [4] demonstrated that under well-drained conditions, facilitated by water flow through a permeable obstacle (and/or permeable ice, cf. [20,21]), the rate of regelation can be enhanced by up to an order of magnitude in comparison with the regelation velocity anticipated under the undrained conditions that pertain when the liquid pressure is constrained to match the ice normal stress. However, their analysis does not hold in the idealized hard-bedded case involving impermeable ice separated from impermeable rock, wherein meltwater flow paths and the attendant hydraulic resistance are tied to thermodynamics.…”