文章基本信息

标题：Shear margins in glaciers and ice sheets
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作者：Raymond Charles
期刊名称：Journal of Glaciology
印刷版ISSN：0022-1430
电子版ISSN：1727-5652
出版年度：1996
卷号：42
期号：140
页码：90-102
DOI：10.1017/S0022143000030550
出版社：Cambridge University Press
摘要：Analytical and numerical techniques are used to examine the flow response of a sloped slab of power-law fluid (power n) subjected to basal boundary conditions that vary spatially across the flow direction, as for example near an ice-stream margin with planar basal topography. The primary assumption is that basal shear stress is proportional to the basal speed times a spatially variable slip resistance. The ratio of mean basal speed to the speed originating from shearing through the thickness. denoted as r, gives a measure of how slippery the bed is. The principal conclusion is that a localized disturbance in slip resistance affects the basal stress and speed in a zone spread over a greater width of the flow. In units of ice thickness H, the spatial scale of spreading is proportional to a single dimensionless number R n ≡ (r/n 1) 1/n 1 derived from n and r. The consequence for a shear zone above a sharp jump in slip resistance is that the shearing is spread out over a boundary layer with a width proportional to R n . For an ice stream caused by a band of low slip resistance with a half-width of w H, the margins influence velocity and stress in the central part of the band depending on R n in comparison to w. Three regimes can be identified, which for n = 3 are quantified as follows: low r defined as R 3 w, for which the central flow is essentially unaffected by the margins and the driving stress is supported entire by by basal drag; high r defined as R 3 > 1w, for which the boundary layers from both sides bridge across the full flow width and the driving stress in the center is supported almost entirely by side drag; intermediate r, for which the driving stress in the center is supported by a combination of basal and side drag. Shear zones that are narrower than predicted on the basis of this theory (≈ R 3 ) would require localized softening of the ice to explain the concentration of deformation at a shorter scale.