Darjeeling Information

In  hilly areas like  Darjeeling, land use practices play a significant role in determining the stability factors of landslide hazards. A close contemplation of the land-use map of Darjeeling Hilly tract, reveals that there are multitude of agricultural activities, tea and medicinal plant plantations, construction works along with forests, rivers, jhoras and many others.

However, the high density population in the hilly areas creates a lot of problems in the  land-use patterns of Darjeeling. The density of population is gradually increasing, which makes the scope of extending agricultural land limited. As a result, the available land falls short to cope up with increasing pressure of population. Naturally, the increasing pressure on forested and other restricted areas cannot be checked.

Landslides in Darjeeling Hill Areas often encourage problems in the land-use patterns. Due to this, the roads have never been examined in respect of  its carrying capacity and  geology. Moreover, the new road construction results in the increased vehicular movements and the rapid growth of trade and commerce. In such roads, heavy traffic movements along with heavy rainfall often cause serious landslides. These days, it has been observed that the increase of the vehicular traffic is incessant, especially heavy vehicles like trucks and buses. In fact, the number of registered vehicles in the hill subdivisions is more than 6500.

Although the length or pattern of the roads in the hilly areas, did not undergo any massive change in the last 50 years, but the number of vehicles, especially goods vehicles like trucks has increased 5 to 7 times than before. Even during night, the traffic movement on the roads continues. Increased vehicular movements cause constant lateral vibrations, thereby making the weaker geological structure becoming more unstable. Apart from the above-mentioned roads, many other roads are maintained by the Forest Department. Some of the major road networks here is (1) the Cart Road from Sukhiapokhri to Maneybhanjan and Batasia, (2) Cart Road from Simkona to Lalkuthi in Darjeeling Forest Division (3) Sukna-Sevok Road in Kurseong Forest Division (4) the Rassium – Labha Cart Road, South Boundary Cart Road, Central Cart Road and Dalgaon Tar Cart Road in Kalimpong Forest Division.

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.

The hilly tract of Darjeeling is rested on the underlying geological structure. Generally, the soils here are formed from fluvial action and lithological disintegration at the same time. Soils developed in the Kalimpong area and its surroundings are essentially reddish in color. However, dark soils are occasional in the area due to the extensive phyllitic and schists. Along the interfluvial areas, the highlands stretching from the west to the east of the district features mixed sandy loam and loamy soil. The southern slopes of Mirik and Kurseong are clayey loam with a reddish hue. The eastern part of river Teesta has sandy soil.

Generally, the nature of soil in the hilly tract of Darjeeling is acidic in nature, which has increased depth indicating the lacking of bases from surface and accumulation in the lower horizons. However, the lateritic type of soil die to excessive weathering has undergone the substantial transformation of the substratum. The regolith has variable thickness depending on the areas and the formation of the soils is subject to the rate of weathering and gradient of the longitudinal slope profiles and the gravity of mass movements. In general, the soil of Darjeeling hills can be categorized into three names- yellow soils, red brown soils and brown forest soils. Red and yellow soils have formed on the base of gneiss, while the brown on the bed of schists and shales. Coarse pale yellow to red brown soils are very common on the Siwaliks, while clayey dark soil characterizes the Daling series.

The bedrock of Darjeeling hills is featured by the grain size composition of the soil. On the Darjeeling gneiss, very coarse-grained (50% -80%) particles can be identified easily. In Damuda and Daling series percentage of sandy and coarse particles are seemingly higher than the other areas. In the Siwaliks, the percentage of silty – clay fraction is higher. A high proportion of potassium (derived from feldspar and muscovite mica) characterizes the chemical content of the soil over Darjeeling gneiss. However, the soil in Darjeeling has poor content of lime, magnesium, iron oxides, phosphorous and nitrogen. As a result, lime is additionally used in the tea plantation areas.