Identification of landslide-prone slopes at Paglajhora area, Darjeeling Himalaya, India
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Susanta Kumar Samanta I Ranjit Kumar Majumdar
Identification of landslide-prone slopes at Paglajhora area, Darjeeling Himalaya, India
Abstract Paglajhora area, located in the southeastern part of the Kurseong town in the Darjeeling Himalaya region, India, experiences frequent slope failure especially in monsoon season. Due to the intricate disposition of major thrust zones (MCT, MBT, etc.), heavy rainfall, neotectonic and anthropogenic activities, etc., the cause of slope failure is not similar all over the area, which makes difficult to categorize the landslides based on their mode of failure. The present work is aimed to demarcate the landslide-prone areas from the surface displacement (horizontal) map derived by optical image correlation (OIC) technique applying normalized crosscorrelation (NCC) algorithm of two temporal Landsat 8 OLI (level 1TP) images, supported by the ground field survey. Results indicate that the overall range of surface displacement (horizontal) rate in the study area varies from 0.4 to 8 m/year out of which the range 0.5–1.5 m/year being dominant classifying the slide type as slow-to-very slow earth flow with a velocity class varying from 3 to 2. Places showing relatively higher displacement values (3 to 8 m/ year) match accurately with the already reported slide zones and the large exposed scarp surfaces noticed during the field surveys or distinguished from the satellite imagery. Areas with lower displacement rates (< 1.5 m/year) experience very slow earth flow, which are confirmed by the presence of cracks and steps on the major roads. Depths of shallow subsurface slip planes are established from dipole-dipole geo-electric surveys in few locations showing moderate surface velocity. Keywords Slope failure . Himalaya . Landsat imagery . OIC . Geo-resistivity Introduction Slope failures are a common natural phenomenon in Darjeeling district in the Eastern Himalayan region. The area is recognized as a famous tourist destination where the bewitching natural beauty of the mountain, the world famous tea gardens, and heritage “toytrain” are considered the main sources of tourist attraction. However, every year, this region suffered several landslides which affect the social and economic life of the local people as well as the population immigrated in this region as a tourist. The occurrence of landslides is due to favourable terrain conditions, which is further activated by excessive rainfall, anthropogenic activities, and earthquakes. As this hilly area is susceptible to slope failure, it strongly hampers the stability, hence, railway service and the production of tea. In the entire stretch of the toy-train route, one of the most landslide-prone zones is the Paglajhora area, located about 8 km away from the Kurseong town towards the east. This region has been witnessing frequent slope failure in the last 50 years, which perturb the movement of toy-train as well as disrupt various economic assets tremendously. As a result, the train service remains close for more than 6 months in a year in thi
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