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lubricated upper surface over which an overlying snow layer may slide. If a solid ice crust is present, any water formed above this crust cannot flow down through it, and when the snow above becomes saturated, additional water will, therefore, run down over the surface of the ice crust. This results in a very wet surface on the ice crust providing a particularly well lubricated surface on which the next higher layer of snow may slide. Thus, where several layers of snow are present, one layer may be wet without the others being wet, and the wet layer is not necessarily the upper layer. It is therefore not enough merely to know that the upper layer of snow possesses good internal cohesion, since it may be lying either on a loose lower layer or on a lubricated lower ice crust, either of which may permit the upper layer, or several layers, to slide away. |
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