Summer Snow Avalanches
During the summer months, as already explained, every type of snow can be found in the High Alps from pure winter powder to the numberless varieties of spring crusts and spring soft snow.
It follows that avalanches in summer obey the same laws as in spring. There are far fewer avalanches in summer than in spring, for there is far less snow to fall. Quite enough, however, is left to make the avalanche problem of vital importance for the ski-runner and the summer climber.
The various types of avalanches described in this chapter are not confined to winter or spring, with the possible exception of the wind-slab avalanche. I should have said, a priori, that wind-slab avalanches were peculiar to winter and the early spring, for they depend for their existence on snow falling at a very low temperature, and on the snowfall being followed by strong and cold winds before the sun has time to melt the snow and to bind it into the underlying surface. I am told by Mr. Young that he has seen wind-slab avalanches in summer—probably, I should imagine, in the very late summer or early autumn, when the conditions begin to approximate to winter conditions. Apart, then, from wind-slab avalanches, which must be very uncommon in summer, all the other types are by no means unusual. Avalanches of powder snow, of old wet snow and new wet snow can occur at any month of the year.
It is not necessary to give separate rules for summer and for spring. The important factors in the problem are not so much the season as the amount of snow that has fallen, the temperature, the angle of the sun, etc. etc. If the reader thoroughly understands avalanche craft in winter and in spring, he should be able to cope with the same or with similar problems in summer.
The majority of fatal avalanche accidents in summer are due to snow slides. I have for convenience’ sake adopted the arbitrary distinction of avalanches into avalanches proper—those which are dangerous owing to the weight and quantity of the snow that falls—and snow-slides, which are only dangerous in so far as they carry the climber or ski-runner with them over a cliff or into a crevasse. Most summer avalanche accidents are due to snow slides, and occur in places which the ski-runner could not reach on ski. Snow resting on ice in gullies, or snow resting on smooth slabs, etc., are frequent causes of fatal accidents. Such avalanches or snow-slides have been described by Mr. Young.
The classical device for testing whether snow is resting on ice—i.e. throwing a big rock down the suspicious slope—is often of use to a ski-runner who is in doubt whether to descend a doubtful slope on ski or on foot.