CAUSES OF LANDSLIDE
There are several causes of landslide.
Some of the major causes are as follows :
1) Geological Weak material :
Weakness in the composition and structure of rock or soil may also cause landslides.
2) Erosion :
Erosion of slope toe due to cutting down of vegetation, construction of roads might increase the vulnerability of the terrain to slide down.
3) Intense rainfall :
Storms that produce intense rainfall for periods as short as several hours or have a more moderate intensity lasting several days have triggered abundant landslide. Heavy melting of snow in the hilly terrains also results in landslide.
4) Excavation of slope :
Excavation of slope and its toe loading of slope/toe, drawdown in reservoir, mining, deforestation, irrigation, vibration/blast, Water leakage from services.
5) Earthquake shaking :
It has triggered landslides in many different topographic and geologic settings. Rock falls, soil slides and rockslides from steep slopes involving relatively thin or shallow dis-aggregated soils or rock, or both have been the most abundant types of landslides triggered by historical earthquakes.
6) Volcanic eruption :
Deposition of loose volcanic ash on hillsides commonly is followed by accelerated erosion and frequent mud or debris flows triggered by intense rainfall.
EFFECTS OF LANDSLIDE
Landslide disasters have both short-term and long-term impact on society and the environment.
The short-term impact accounts for loss of life and property at the site and the long-term impact includes changes in the landscape that can be permanent, including the loss of cultivable land and the environmental impact in terms of erosion and soil loss, population shift and relocation of populations and establishments.
Like in any other disaster. the most affected are the socio-economically weaker sections of the society who inhabit the vulnerable areas.
They have meagre(inadequate) sources of livelihood, which when wiped out by a hazard, leaves them without any food or shelter. Apart from this, the injuries and casualties suffered add to the woes of the affected families.
The biggest loss is that of private and government property, as well as damage to or destruction of infrastructure and heritage structures.
The frequent obstructions caused to the movement of traffic by numerous landslides during the rainy season, sometimes for days together, particularly in the Himalayan and North-Eastern regions of the country, bring untold misery to the people inhabiting the villages and townships in the landslide-prone hilly regions.
Landslides also reduce the effective life of, and returns from hydroelectric and multipurpose projects by adding an enormous amount of silt load to the reservoirs.
Landslide dams result in the flooding of large upstream areas. Further, if the dam fails, it causes flooding and large scale devastation in downstream areas.
Also, solid landslide debris can ‘bulk’ or add volume and density to otherwise normal stream flow or cause channel blockages and diversions creating flood conditions or localized erosion.
Landslides can also cause overtopping of dams resulting in flash floods or reduced capacity of reservoirs to store water.