If a sally is attempted in bad weather from a hut which is situated among glacier snow-fields, it is advisable to cut up a number of small stakes from the firewood. These can be planted in the snow at intervals of a hundred yards or so in order that a retreat can always be made back to the hut if further advance is impossible.
Snow Conditions in the High Alps.
If the Alps were windless, the snow that falls between November and the end of February would remain powdery and unspoiled on all save very steep south slopes. At high altitudes the sun is powerless to affect the snow in midwinter on gentle south slopes. The snow would remain powdery on northern slopes till the middle of April but for wind. Unfortunately, the High Alps are swept by wind, more especially during long spells of fine cloudless weather, during which the ‘bise,’ or north wind, sweeps across all exposed ridges and faces. Consequently, the snow seldom remains long unspoiled. In sheltered glacier valleys it may retain its powdery condition, but on all more or less exposed slopes it soon hardens. Of course, if an expedition is planned within two or three days of a fresh snowfall, the party may have perfect powder snow; but such snow is the exception in winter in the High Alps, whereas it is the rule in spring.
Rock Ridges and Ice Slopes.
Rock climbing does not properly come within the scope of mountaineering on ski; but so many ski-runners combine a ski tour with a final scramble up a rock ridge, such as the last arête of Monte Rosa or the Zinal Rothhorn, that some discussion of the condition of rocks and ice slopes in winter is essential.
As a rule, rock ridges are as dry, or drier, in winter than in summer. Snow that falls in summer often falls at a temperature little below freezing. It is often most adhesive stuff. The strong summer sun followed by frosts at night turns this snow into crust, or at least into snow with a considerable power of sticking to the rocks. In summer it is often several days before the big rock peaks will go after a heavy snowfall. But in winter the snow that falls in the High Alps is light and powdery. The low temperatures and the reduced power of the sun prevent the snow melting; it retains its light powdery character, and is swept away from exposed ridges by the wind. It offers no resistance to the wind, for it is composed of light dry crystals with no cohesive or adhesive power. Consequently, the rock ridges in the winter are often freer from snow than in average summer weather, which is a mixture of good and bad. In winter, cornices have little chance of forming. In fact, if the weather is mild and the ridge windless on the day of the ascent, it is scarcely more difficult to climb a rock ridge of average difficulty in winter than in summer. South ridges are, of course, much warmer than north ridges, but they are not necessarily more free of snow; for the agent that reduces the snow on the rock ridges is not the sun—powerless as a melting agent at these altitudes in winter—but the wind; and in fine weather the wind, as often as not, blows from the north. Of course, if the north wind is blowing, a north ridge may be impossible, for the rocks promptly become extremely cold to touch, so that in general it is wisest to select south rock ridges in preference to north. None the less, rock ridges facing north, such as the north ridge of the Zinal Rothhorn or the north ridge of the Gspaltenhorn, have been climbed without difficulty in midwinter.[22]
The same causes which keep the rock ridges comparatively free from snow tend to remove any snow that may fall on to steep ice slopes.
Inexperienced winter mountaineers are often surprised to find as much or more ice on summit slopes in winter than in summer.
As a matter of fact, there is often quite as much ice on steep exposed slopes in winter as in summer.
An ice slope is transformed into a snow slope when falling snow is accompanied by a temperature just above freezing-point—in other words, when the snow is very nearly sleet. Such snow adheres to the underlying ice, and by the normal process of alternate thaw and frost becomes more and more firmly attached. The next snowfall that occurs attaches itself to the underlying thin stratum of snow crust lying on ice, so that in the course of time the ice slope is covered by a compact and reliable layer of crusted snow.