Avalanche often happens in the mountain. Some avalanches happen in strong snowstorm, but others commonly occur in the area that snow accumulation is too thick, whose thickness is more than the frictional resistance on the surface of the earth. One of the reasons for the avalanche is that the deep "white frost" forming slowly under the snow, which is a kind of the hexagonal cup of ice crystal and like small pieces of ice that we usually see.
The frost formation was caused by evaporation of the snow grains and they are looser than the upper of snow, forming a soft belt beteen the snow on the ground or underneath the earth and snow on the top the the mountain. When the upper snow begins to slide down the hillside, the soft belt plays a lubricant role, which not only accelerates the speed of the snow, but also drives surrounding still snows. People may not be aware of the struggle on the snowy mountains but it indeed exists: gravity pull the snow down, but the cohesion of the snow is expected to keep the snow in place.
When the battle achieve climax, even we force a little bit of outside power, such as running of animals, rolling stones, wind, slight vibration, even a shout in the valley, a destructive avalanche will occur as long as the pressure exceeds the cohesion that makes snow grains be together. For example, the wind not only causes a lot of snow to accumulate, but also causes the snow grains to condense, forming a hard and brittle snow layer so that the upper snow layer can slide along the under snow layer and avalanche happens. However, apart from the slope form, the avalanche is largely dependent on human activities. Experts estimate that 90 percent of the avalanches are caused by victims or their teammates, an avalanche known as the "artificial leisure avalanche".
Skiing, hiking or other winter sports enthusiasts often inadvertently become the fuse of an avalanche. If a man was buried under the snow for half an hour, the chances of survival will be very slim.
We often see such reports that somebody has been killed in an avalanche while skiing. But at that time, it was not clear whether the avalanche is active to harm people or kill people due to the influence of human movements.
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