The share of avalanches account for about 50% of accidents in the mountains. The condition for the formation of avalanches is a mountainous snow-covered slope of 15 - 30°, heavy snow with the intensity of growth of 3 - 5 cm/h. the Most avalanche-prone periods of the year are imawesa — at this time is recorded up to 95% of the avalanches. An avalanche can come at any time of day this occurs most often during daylight hours - 68% night 22% or evening - 10%.
The movement of the avalanche starts in the conditions when the component of the force of gravity of the snow cover in the direction of the slope exceeds the cohesive forces of the snow crystals together. Before you start moving snow masses are in a state of unstable equilibrium.
The reasons for the motion of avalanches:
heavy snowfall or accumulation of a large amount of snow on the slopes when carrying it by the wind;
a small force of adhesion between the underlying surface and the newly-fallen snow;
the thaw and rain, followed by the formation of slippery water layer between the underlying surface and fresh snow;
a sharp change in air temperature;
mechanical, acoustic, wind influence on snow cover.
The speed of avalanches is 20 — 100 m/s. Pressure (impact force) of the avalanche can amount to tens of tons per square meter.
Factor affecting avalanches is a huge destructive force. The avalanche swept away everything in its path, in the mountains damage and destroy structures, communications, power lines, roads, equipment, injure and kill people. The main cause of death in avalanche is suffocation (asphyxia). During the movement of an avalanche to breathe it is almost impossible, the snow clogs the Airways, snow dust gets into the lungs. In addition, a person may freeze, to mechanical injuries to the head and internal organs, broken limbs or spine. This is the result of hitting the ground, rocks, trees, stones.
Avalanche protection includes:
the study, monitoring, forecasting and informing the population about the possible threat of avalanches;
teaching people safe operations in avalanche areas;
artificial induction of avalanches;
the use of avalanche plantings;
the avalanche creation in the field of engineering structures, including canopies, tunnels, corridors.
With the threat of avalanches closed the ski slopes, mountain roads, Railways, prohibited the exit of people into the mountains, aktiviziruyutsya the work of rescue groups. The collapse is the separation and falling of large masses of rocks with steep and precipitous slopes to river valleys, sea coast due to loss of adhesion of the detached mass, with the parent base. Falls can injure people, destroy transport routes, blocking technique to create a natural dam with the consequent formation of lakes, cause an overflow of the huge amount of water from the reservoirs.
Landslides are:
large — mass 10 million m3 or more;
medium — weight from several hundred up to 10 million m3;
small — a few dozen cubic meters.
The formation of landslides contributes to the geological structure of the area, the presence on the slopes of the cracks.