The verification and significance of three approaches to longitudinal stresses in high–resolution models of glacier flow

Abstract

Hubbard, A., 2000: The verification and significance of three approaches to longitudinal stresses in high-resolution models of glacier flow. Geogr. Ann., 82 A (4): 471-487.ABSTRACT. With the purpose of improving the ice physics underpinning time-dependent glacier flowline models, three independent approaches for solving longitudinal stresses in glaciers are discussed and verified by application to Haut Glacier d'Arolla. To highlight any shortcomings, the reduced and much utilised driving stress approximation is also applied and compared. Modelled velocity patterns using the three full stress schemes exhibit consistency with one another and good coincidence with observed velocities for the 1991 summer melt season. Furthermore, these stress patterns indicate that longitudinal stresses are significant and of a similar order of magnitude as the basal shear stress components. However, the driving stress approximation yields erratic fluctuations in the stress and velocity fields which are neither realistic in terms of mass continuity nor agree with observations. Basal decoupling experiments indicate a complex relationship between basal velocity and englacial stresses with considerable dampening of any basal perturbation occurring as it is dissipated towards the surface and transferred throughout the ice mass. The driving stress approximation fails to account at all for any such coupling. Experiments to identify the length scale over which longitudinal effects operate indicate that they are significant even up to 10 ice thicknesses. The implication here is that longitudinal stresses play a significant role in determining glacier dynamics on length scales up to at least 2 km and that the predictive power of models of glacier flow based purely on the driving stress approximation is therefore subject to significant limitations. Inclusion of longitudinal stresses overcomes one of the main limitations imposed on such models and, given the potential ease of incorporation of the schemes described here, this deficiency may readily be resolved.

A Coupled Ice‐Sheet/Ice‐Shelf/Sediment Model Applied to a Marine‐Margin Flowline: Forced and Unforced Variations

“…Our equations fall into type L1L2 of Hindmarsh's (2004) categorization of various approximate schemes, which is found to yield relatively accurate results. Using a similar technique to ours, Hubbard (2000) found that results for a valley glacier agree well with those using a higherorder model. Hindmarsh (1993Hindmarsh ( , 1996 and Hindmarsh and Le Meur (2001) have investigated whether the dynamics of the narrow transitional region near the grounding line matter for overall equilibrium and stability properties, but these issues remain unresolved.…”

High-resolution numerical simulation of Younger Dryas glaciation in Scotland

“…Ice flow occurs through internal deformation and Weertman (1964)-type sliding when basal temperatures reach the pressure melting point, and which is adjusted with a dimensionless scaling factor. Longitudinal stresses become increasingly important in high resolution models such as the one used here, and are computed using an empirically validated ice-stretching algorithm (Hubbard, 2000).…”

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