Transfer of Basal Sliding Variations to the Surface of a Linearly Viscous Glacier

• Published in: Journal of Glaciology
• Main Authors: Balise, Michael J., Raymond, Charles F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1985
• Subjects: Earth-Surface Processes; Journal of Glaciology
• Online Access: http://dx.doi.org/10.1017/s002214300000664x; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002214300000664X

Abstract The transfer of basal velocity anomalies to the surface of a glacier is investigated using a model of a planar parallel-sided slab (thickness H ) of linear viscous rheology. Surface velocity parallel ( u s ) and normal ( v s ) to the surface is calculated for various spatial distributions of basal velocity anomalies with components parallel ( u b ) and normal ( v b ) to the surface. Four scales of differing behavior can be identified depending on the spatial length L of the basal anomalies. At very short scales ( L ≤ 1 H ) there is essentially no response at the surface. At short scales (1 H ≤ L ≤ 5 H ), a basal anomaly u b induces a response in both u s and v s . The spatial pattern of u s is such that velocity peaks in u s can be shifted from peaks in u b , and may differ in number. The amplitude of u s is up to about 0.3| u b |. The amplitude of the cross-component effect v s may be greater than the amplitude of u s . A basal anomaly v b induces a response in both v s and u s. The pattern of v s is the same as the pattern of v b , and the amplitude of v s is up to about 0.7 | v b |. The amplitude of the cross-component effect u s is less than the amplitude of v s . At intermediate scales (5 H ≤ L ≤ 10 H ), results differ from the short scale in two respects; velocity peaks in u s correspond with peaks in u b and surface amplitudes are increased, except for cross-component effects for which surface amplitudes are of the same order as at the short scale. These cross-component effects at the short and intermediate scales show in particular that substantial anomalous surface-normal motions can be induced by deformation, even though the basal velocity anomaly is parallel to the surface. At long scales (10 H ≤ L ), the velocity anomaly at the surface is essentially the same as the anomaly at the bed. For all scales, the longitudinal strain-rate averaged over depth is larger in magnitude than the longitudinal strain-rate at the surface and, at the short scale, it may differ in sign, so that v s cannot be ...