Landslides and Its Causes in Darjeeling
Landslides are very common in Darjeeling and the layout of Blockwise landslide affected areas shows the comparative intensity of landslides in respective blocks. According to the layout report, Kalimpong I, Kalimpong II and Rangliot blocks are known to be severely vulnerable regarding landslides. The chances of landslides are also high in the wide region of Kurseong and some parts of Bijanbari and Gorubathan blocks.
However, the condition is increasingly vulnerable in Kalimpong sub-division. In this region, the land under agriculture is more than that of the area under plantation or forests. All the more, the maximum of its agriculture includes the cultivation of root crops like potato, ginger, cardamom and onions. Extensive cultivation of root crops and harvesting them just after monsoon affects the bonding of the underground soil by changing its cohesiveness. Loose bonding of the soil makes it vulnerable to erosion.
However, heavy vehicular movement increases instability of the slopes along the main route. It encourages the frequency of landslides along the roads, especially during rainy season.
Extensive quarry operation also causes environmental hazards, which is considered threatening to the soil. The illegally operated quarries along the Lish and Gish basin and Tindharia region affect the slope stability, and laden the rivers and their tributaries with excessive amount of silts, which ultimately ends up with extensive siltation throughout the riverbeds and the adjacent plains. Excessive siltation disturbs the ecological equilibrium of the area. Apart from coal mining, stone quarrying from the slope especially under the main road causes occasional slope failure.
To determine the landslide frequency, experts have prepared the Critical Area Zonation map. It examines the geology, soil, and climatic factors along with land use pattern. The map denotes that Grid no. E4 under Rangli-Rangliot block, G4 and H5 under Kalimpong II Block as the most landslide prone areas, however, the major cause of the landslide hazard is human intervention.
The experts believe that although soil erosion and its conservation are important to cause landslides, the evolution or rising of young mountains is the basic reasons for frequent landslide hazards in the Himalayan region. The rise of young mountains accentuates unstable geological structure, tectonic disturbances, parallel subsidence of Himalayan slopes.
The soil of Darjeeling hilly tract comprises of gneiss, schists and Phyllites. Soil erosion increases these days due to extensive root crops cultivation. Moreover, the hilly areas is devoid of any soil deposition. As a result, hilly tracts are vulnerable to soil erosion. Finally, the excessive amount of forest depletion also makes the hilly soil severely vulnerable.
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