Sliding over anisotropic beds
Many glacier beds are anisotropic, by which is meant that the dominant wavelengths are different in the two map-plane directions. A largely unexplored consequence of Nye-Kamb sliding theory is the fact that an anisotropic bed can produce a sliding velocity not parallel to the tangential traction vec...
| Published in: | Annals of Glaciology |
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| Main Author: | |
| Format: | Article in Journal/Newspaper |
| Language: | unknown |
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International Glaciological Society
2000
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| Online Access: | http://nora.nerc.ac.uk/id/eprint/20577/ https://doi.org/10.3189/172756400781820840 |
| Summary: | Many glacier beds are anisotropic, by which is meant that the dominant wavelengths are different in the two map-plane directions. A largely unexplored consequence of Nye-Kamb sliding theory is the fact that an anisotropic bed can produce a sliding velocity not parallel to the tangential traction vector. This has important consequences, since observations of non-parallel flow are often taken as indications that the shallow-ice approximation has broken down, whereas this need not be the case with an anisotropic bed. Mathematically, this effect can be incorporated through the use of a sliding tensor. The mathematical properties of this tensor are outlined, and the correct "invariant" for the sliding law, a quadratic form, is deduced. Nye-Kamb theory for anisotropic beds is discussed. Flow on the infinite plane and the properties of surface-topography diffusion are elucidated. The properities of kinematic waves and shock waves are discussed. Kinematic waves can have a lateral component. Numerical computations of ice-sheet flow on beds with anisotropic roughness are presented, with emphasis placed on how this affects divide-ridge structure. It is suggested that cold-based ice sheets, which have an anisotropic bed affecting the shear layer, may also show non-parallelism of surface slope and velocity. |
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