As landslides involve movement of mass of rock, mud’s etc., down a slope, factors that promote such movement of mass provide the causes for landslides. Such causes can arise from a number of happenings. For example;
(a) Increase in the mass of weak rocks, clay and other debris likely to slide;
(b) Loosing of breaking of rocks and soil by wetting due to rain, weathering, erosion, deforestation, earthquake, and tremors and similar other events;
(c) Increase in the tilt or slope due to seismic disturbances or construction activities, mining, quarrying etc.
It is evident from the above that the causes for landslides are both natural and man-made.
While the above-mentioned causes are basically responsible for landslides, it is quite often that a triggering mechanism starts the disaster. Conditions favorable for a landslide continue to build up and a final small cause triggers a landslide. This small cause or trigger can occur in many ways. It could be the seepage of water inside rock crevices; vibration from blasting, earthquake, or even thunder; erosion from water streams; deforestation; weakening due to digging and quarrying. It could even be the continued loading due to snow accumulation or collection of large amount of rainwater.
These are generated due to the structural failure of snow heap lying on mountain slopes. Such structural failure may occur due to:
(a) External stresses caused by (i) large accumulation of snow from heavy snowfall creating excessive loading, (ii) movement of persons, animals and (iii) sound waves from any loud noise like a sharp whistle, gunfire, thunder;
(b) Metamorphic activities, I. e. physical happenings within the snow mass which would create weak layers inside it; and
(c) Excessive melting of upper layer of snow mass resulting in seeping of melts water under the snow mass and lubricating the bottom surface of the snow mass to enable it to slip and create a snow avalanche.
In general, snow avalanches occur when extreme winter conditions (sub-zero temperatures) prevail for long duration and heavy snowfall occurs over smooth, glaciated slopes, which are devoid of vegetation cover. Sometimes, strong winds blow and drift accumulated snow from avalanche-free areas to avalanche-prone slopes thus causing a snow avalanche.