Читать книгу Winter Climbs in the Cairngorms. The Cairngorms and Creag Meagaidh онлайн

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Although general observation is important, a simple snow pit can give further information about the snowpack and its stability. A snow pit dug in a safe but relevant position for the suspect slope is useful. It is dug down to ground level or, more usually, to the level of a stable consolidated layer. The back or sidewall of the pit is inspected for snow layers of differing hardness. Significant differences in hardness between adjacent snow layers can be a warning sign. A pit can be dug quickly with an axe and need not be elaborate to give relevant information. Even the resistance felt when pushing the axe into the snow may reveal much about the layers. However, due to local variations in the properties of snow, any snow pit or test will only give information about one point, and must be considered as part of the overall picture.

Route choice and safety precautions

A number of factors influence route choice in avalanche terrain (here route choice is not limited to a climb, but includes all movement in the mountains). Ridges, buttresses and flat ground are safer than open slopes. Windward slopes are generally safer than lee slopes, but even here local variations in topography can create a localised avalanche hazard. Convex slopes are more likely to slide than concave ones, and gullies or depressions tend to concentrate avalanche depth and power. Even a very small area of windslab can represent a hazard if the run-out is into rocks, over a drop, or into a terrain trap such as a stream-bed or similar hollow where the debris can be funnelled and build up to considerable depths. Some very serious accidents have occurred where the slab that released was only about the size of a mattress.