Avalanche
Death comes quickly in the mountains. Each winter holidaymakers are caught unawares as they happily ski away from the fixed runs, little realizing that a small avalanche (雪崩) can send them crashing in a bone - breaking fall down the slope and leave them buried under tons of crisp white snow. There are lots of theories about how to avoid disaster when hit by an avalanche. Practice is normally less cheerful.
The snow in the Salzburg of Austria where a recent disaster took place was typical avalanche material. For several days before the incident I had skied locally. Early winter snow was wearing thin and covered with ice. On top of that new, warmer flakes were gently falling to produce a erous carpet. To the skier who enjoys unmarked slopes it is tempting stuff, deep new powder snow on a hard base——the skiing that dreams are made of. And sometimes nightmares.
Snow falls in sections like a cake. Different sections have different densities because of the temperatures at the time of the fall and in the weeks afterwards. Problems come when any particular section is too thick and not sticking to the section beneath. The snow of the past few weeks had been falling in rather higher temperatures than those of December and early January. The result of these conditions is that even a slight increase in the temperatures sends a thin stream of water between the snow new and the old. Then the new snow simply slides off the mountain.
Such slides are not unexpected. Local citizens know the slopes when tend to avalanche and the weather in which such slides are likely. Traps are set to catch the snow or pr it slipping; bombs are placed and exploded from time to time to set off small avalanches before a big one has time to build up; and above all, skiers are warned not to ski in er areas.
In spite of this, avalanches happen in unexpected areas and, of course, skiers ignore the warnings. The one comfort to recreational skiers, however, is that avalanche incidents on the marked ski slopes are quite rare. No ski resort wants the image of being a death trap.
It would appear from the text that avalanches are brought about because ________.