Abstract
AbstractResults 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.
Highlights
Flow of marine-terminating ice streams accounts for most of the mass lost from the Antarctic Ice Sheet (Rignot and others, 2019) and about half of the mass lost from the Greenland Ice Sheet (IMBIE Team, 2020)
Ice softening by interstitial water that localizes strain in ice-stream shear margins (Haseloff and others, 2019) creates troughs at their surfaces that accelerate ocean-driven break-up of ice shelves (Alley and others, 2019)
Consideration of Poiseuille flow through melt-filled vein networks bounding grains under a head gradient dh/dx yields the specific discharge: q r4 d2 rg m dh dx where d is the grain diameter, r is the radii of individual veins, and B is a dimensionless constant that depends on the vein crosssectional shape and vein network geometry (Fig. 1) (e.g. Frank, 1968)
Summary
Flow of marine-terminating ice streams accounts for most of the mass lost from the Antarctic Ice Sheet (Rignot and others, 2019) and about half of the mass lost from the Greenland Ice Sheet (IMBIE Team, 2020). Fast flow of these glaciers is regulated fundamentally by water. Water production in shear margins controls the supply of water to the underlying bed This basal water helps control the lateral distribution of basal effective stress and drag (Suckale and others, 2014; Perol and Rice, 2015; Meyer and others, 2018; Haseloff and others, 2019). Where d is the grain diameter, r is the radii of individual veins, and B is a dimensionless constant that depends on the vein crosssectional shape and vein network geometry (Fig. 1) (e.g. Frank, 1968)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call