Page 250 - Health, Population and Environment Education 9

or increased load due to precipitation, Avalanches initiated by this process are known as
spontaneous avalanches. Avalanches can also be triggered by other loading conditions
such as human or biologically related activities. Seismic activity may also trigger the
failure in the snowpack and avalanches.
Most avalanches occur spontaneously during storms under increased load due to snowfall.
The second largest cause of natural avalanches is metamorphic changes in the snowpack
such as melting due to solar radiation. Other natural causes include rain earthquakes,
rockfall and icefall. Artificial triggers of avalanches include skiers, snowmobiles and
controlled explosive works.

By their nature, avalanches represent a major danger only in mountainous areas of the
earth where geographic and meteorological conditions give rise to heavy rains and to a
accumulations of snow and ice prone to hurtling down in the valleys inhabited by man. A
distinction can be made between two types of avalanches.
1. Large- scale avalanches caused by very heavy rains, which threaten localities,
buildings and communication links in all or parts of a valley.
2. Avalanches restricted to smaller local areas, which are mostly triggered by man in the
course of his professional or sporting activities.
The damaging effects of avalanches may be widespread or limited depending on the factors
which provoked them. But just as in the case of landslides, a very localised incident can
have consequences beyond its immediate surroundings, notably when communication
links such as roads, railways and cable cars are interrupted or infrastructure is destroyed

Preventive and protective measures of avalanche
Areas at risk from avalanches can generally be identified by observation of the mountain
slopes and by the study of the local records of past disasters.
Preventive measures will consist in identifying these likely zones and in the adhoc layout,
planning and implanting of buildings to prevent the triggering of serious avalanches.

At the community level the consequences of avalanches by the following protective and
preventive measures:

1. Selective monitoring of the snow and the danger of avalanches through the
establishment for this purpose of a national institute of studies.
2. Land surveys and mapping of avalanche zones should be done.

3. Land development and planning regulations forbidding building or residing in
threatened zones.

4. Constructing building which will prevent the triggering of massive avalanches on the
uphill slopes and infrastructures such as walls, barriers, tunnels, and galleries which
will protect threatened property.
5. Depending on the seriousness of the danger from avalanches, forbidding circulation
or the use of certain communication routes, i.e. roads, railways etc.
6. Planning the evacuation of the population and livestock at risk.
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