Abstract
Abstract. Shear stress at the base of glaciers exerts a significant control on basal sliding and hence also glacial erosion in arctic and high-altitude areas. However, the inaccessible nature of glacial beds complicates empirical studies of basal shear stress, and little is therefore known of its spatial and temporal distribution. In this study we seek to improve our understanding of basal shear stress using a higher-order numerical ice model (iSOSIA). In order to test the validity of the higher-order model, we first compare the detailed distribution of basal shear stress in iSOSIA and in a three-dimensional full-Stokes model (Elmer/Ice). We find that iSOSIA and Elmer/Ice predict similar first-order stress and velocity patterns, and that differences are restricted to local variations at length scales of the order of the grid resolution. In addition, we find that subglacial shear stress is relatively uniform and insensitive to subtle changes in local topographic relief. Following the initial comparison studies, we use iSOSIA to investigate changes in basal shear stress as a result of landscape evolution by glacial erosion. The experiments with landscape evolution show that subglacial shear stress decreases as glacial erosion transforms preglacial V-shaped valleys into U-shaped troughs. These findings support the hypothesis that glacial erosion is most efficient in the early stages of glacial landscape development.
Highlights
The widespread late-Cenozoic glaciations produced distinctive glacial landforms in many mid- to high-latitude mountain ranges (e.g. Penck, 1905; Sugden and John, 1976)
In order to test the validity of the higher-order model, we first compare the detailed distribution of basal shear stress in iSOSIA and in a three-dimensional full-Stokes model (Elmer/Ice)
We find that iSOSIA and Elmer/Ice predict similar first-order stress and velocity patterns, and that differences are restricted to local variations at length scales of the order of the grid resolution
Summary
The widespread late-Cenozoic glaciations produced distinctive glacial landforms in many mid- to high-latitude mountain ranges (e.g. Penck, 1905; Sugden and John, 1976). A few studies have measured sliding velocity and basal stress directly; examples include the Glacier d’Argentière in the French Alps (Boulton et al, 1979) and under Engabreen in Norway (Cohen et al, 2000, 2005; Iverson et al, 2003). These studies measured regional shear stress values between 0.1 and 0.3 MPa. These studies measured regional shear stress values between 0.1 and 0.3 MPa Interpretations from these studies are complicated by their limited spatial and temporal extent, and by local heterogeneity such as the presence of cavities that might concentrate stress at much higher values. Despite several complications in such studies (Joughin et al, 2004; Gudmundsson and Raymond, 2008; Habermann et al, 2012), and very different subglacial settings, these studies find basal shear stress of the order of 0.1–0.4 MPa
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