The basic forecast in these events is that of rainfall (or snowfall) and strong winds but additional factors have to be kept in view. For landslides, the strength of the rock and any damage already occurred at ground have to be considered.
Heavy rains and heavy snowfalls initiate these phenomena. Further, these occur more frequently in areas, which are prone to these disasters due to the peculiar local geological features such as weakness of soil or rock.
Landslides and snow avalanches affect the remotely located often isolated, small communities in villages or hamlets in the mountain regions of the country where external assistance takes time to reach in times of emergency when the normally difficult terrain and tracks ,may become almost impossible to negotiate.
Webster’s Third New International Dictionary (1971) defines these phenomena as follows: Landslide: Rapid downward movement, under the influence of gravity, of a mass of rock, earth or artificial fill on a slope. Also, the mass that moves or has moved downwards.
The following are highly vulnerable to landslides and snow avalanches: (a) Deforested mountains especially in areas of heavy rainfall or snow fall; (b) Settlements (villages or hamlets) that are built on hill tops, steep slopes, softer soil.
In order to consider risk reduction measures, we should first have an idea of likely risks from landslides and snow avalanches. These are as follows:
In considering the effects and impacts of landslides and snow avalanches, the following special features of these hazards should be kept in mind.