Elmer/Ice News

Parameterization of lateral drag in ice flowline models

cross section2Adhikari and Marshall (2012) employ Elmer/Ice model to identify two distinct sources of lateral drag (i.e., geometry-induced and slip-induced drag). Effects of both sources of lateral drag have been systematically parameterized for flowline models of glacier dynamics.

Abstract: Given the cross-sectional geometry of a valley glacier, effects of lateral drag can be parameterized in flowline models through the introduction of Nye shape factors. Lateral drag also arises due to lateral variability in bed topography and basal flow, which induce horizontal shear stress and differential ice motion. For glaciers with various geometric and basal conditions, we compare three-dimensional Stokes solutions to flowline model solutions to examine both sources of lateral drag. We calculate associated correction factors that help flowline models to capture the effects of lateral drag. Such parameterizations provide improved simulations of the dynamics of narrow, channelized, fast-flowing glacial systems. We present an example application for Athabasca Glacier in the Canadian Rocky Mountains.

Relationship between age and depth at ice divides

isochronesIn Martìn and Gudmundsson (2012), effects of nonlinear rheology, temperature and anisotropy on the relationship between age and depth at ice divides is investigated using Elmer/Ice. 

Abstract: Ice flow in divide areas is strongly anisotropic. The evolution of ice fabric, from the onset of divide flow towards steady state with a fully developed fabric, has been shown to profoundly affect both the stratigraphy and surface topography of ice divides. Here, we investigate the effects of ice flow on the age-versus-depth relationship at ice divides by using a full Stokes thermomechanical model with a non-linear anisotropic constitutive relation between stress and strain rates. We compare our results with analytical approximations commonly employed in age–depth predictions, such as the Dansgaard and Lliboutry approximations. We show that these approximations systematically underestimate the age of ice at fully developed divides by as much as one order of magnitude. We also show that divides with fully developed fabric are ideal locations for ice-core extraction because ice under them can be up to one order of magnitude older than ice at the same depth at the flanks. In addition, these divides have a distinctive morphological structure that allows them to be clearly identified from satellite imagery or ground-penetrating radar data.

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