What is an avalanche: An
avalanche is a mass of snow which is set in motion by its own weight through a
violent disturbance of its equilibrium. There are two kinds of avalanches; the
surface avalanche, in which only the top covering of snow slips, and the ground
avalanche, in which the whole mass is carried away. A dreaded hazard. Often the
victims are not individual climbers but whole group in the area. Prudent
climbers and experienced mountaineers have also been killed or injured in
avalanches. The secret lies in keeping off the dangerous slopes at the correct
time, and also in knowing the conditions that cause avalanches. The subject
requires thorough study of the causes, precautions, and conduct if caught in an
avalanche.
The formation of avalanches: In
summer, there are slides of stones and ice but relatively fewer avalanches,
because of the stabilised snow. However, an increasing number of climbers are
taking to the mountains in spring and even in winter. In addition to good
technique, this demands a close knowledge of the mountains, because in winter
and spring the snow not being stabilised there is the danger that sometime an
avalanche will occur. The formation of an avalanche depends on the nature of the
terrain, the quality/ quantity of the snow and the temperature.
The nature of the terrain: Slippery
surfaces, turf, flattened grass, slabs of laminated rock or smooth rock,
under-layers of hard snow or ice, all these are surfaces on which avalanches are
likely to occur because the snow does not cling to them.
The contour of the terrain: Convex
slopes are more dangerous than concave ones which flatten out at the base.
Similarly with the incline any slope of under 15 degrees is safe, provided that
it is not dominated by steeper slopes. Snow slabs are dangerous above 15 degree
onwards. Fresh snows (powdery and wet) are dangerous from 25 degree onwards;
compressed powder snows, and spring snows, are safe upto 30 degrees. Most of the
dangerous avalanches originate on slopes between 30 and 45 degrees. Be careful
when you are on such slopes.
The nature of the snow: Instability
increases with the thickness of the covering, but also according to the physical
characteristics of snow. Fresh snow and snow which does not adhere (powder snow
or moist snow on a wet base) are the most unstable.
Temperature: When
the temperature rises, the snow humidifies and becomes heavy and therefore
unstable. Cold on the other hand stabilizes it by causing the crystals to
interlock. In summer, after fresh snowfall, one should wait two or three days
before setting out on a climb.
How avalanches are triggered off:
In certain terrain and under certain conditions avalanches
can be predicted but sometimes they start unexpectedly when the top layers of
snow become detached by a sudden disturbance of their mechanical or thermal
equilibrium.
Failure of mechanical equilibrium:
This may be caused by the passage of a climber or a skier,
particularly if he is traversing the mountain slope. Overloading of a slope by
several climbers and skiers; fall of a cornice, or falling seracs or stones,
vibrations of the atmosphere can trigger off an avalanche particularly on slopes
with powder snow.
