Longitudinal Stress Gradients and Basal Shear Stress of a Temperate Valley Glacier

• Published in: Journal of Glaciology
• Main Author: Bindschadler, Robert
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1979
• Subjects: Earth-Surface Processes; Journal of Glaciology
• Online Access: http://dx.doi.org/10.1017/s0022143000015148; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000015148

Abstract For the first time field data from a temperate valley glacier, the Variegated Glacier, are used to investigate the behavior of longitudinal stress gradients predicted by the relation (1) where H is the local depth, and y s and y b are the surface and bed elevations respectively. This equation is similar to one derived by Budd (1970) for plane strain-rate, to evaluate the importance of longitudinal stress gradients, but a shape factor f is included to account approximately for lateral strain-rate gradients. Predictive numerical models of valley glaciers require the local base shear stress to be known as accurately as possible. It has been argued on theoretical grounds that when T is averaged over distances of more than five to ten times the depth, this term is negligible. At larger averaging scales, 2 G can then be considered a correction to the simple geometric expression of base stress due to the presence of longitudinal stress gradients. Field data of velocity and geometry are used to evaluate the terms of Equation (1), where τ b and 2 G are estimated as and at intervals of 100 m, U s is the measured surface center-line velocity, A and n are the flow-law parameters, and is the surface longitudinal strain-rate. The expression for 2 G is an approximation proposed by Budd (1970).