One of the most outstanding features of ice crystals is that no two have ever been found to be alike despite their simple, six-sided symmetry – but this beautiful shape also means that they respond to pressure and stress in a complex manner. They will deform primarily along one axis rather than identically along all axes, a quality called anisotropy.
Polar ice sheets experience different levels, directions and types of stress in different regions. In particular, there are large differences in the stresses in the ice between land-based and floating ice, which leads to characteristic arrangements of all crystals in these areas.
Ma Ying and his colleagues have developed a model which allows them to interpret the effect of crystal orientation in the ice on its flow behaviour on large scales. They find that anisotropy makes ice softer and more deformable where it rests on land, suggesting that simpler ice-sheet models may have underestimated the speed at which ice flows towards the sea. Conversely, they find floating ice to be stiffer if crystal orientation is taken into account because very different stresses act on the ice here. Their findings highlight the importance of understanding and modelling ice anisotropy in order to understand how it affects ice-sheet flow towards, and in, the sea.
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Ma Ying, O. Gagliardini, C. Ritz, F. Gillet-Chaulet, G. Durand, and M. Montagnat (2010), Enhancement factors for grounded ice and ice-shelf both inferred from an anisotropic ice flow model, Journal of Glaciology, 56, 805-812.