Introduction - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 12

higher Himalayan range in the higher reaches of Sikkim-Darjeeling Himalayas
(Chakraborty et al. 2011 ). This earthquake invited cracks and subsidence of roads
along Nathula-Gangtok Highway (Fig. 1.4 ). The new landslides that occurred in the
lower elevations are mostly concentrated within the terrace deposits of trunk
streams such as Tista, Rangit and Balason etc. (Fig. 1.5 ) and within the old colluvial
deposits on the lower reaches of slope adjacent to trunk streams (e.g. Jorethang-
Rishi-Legship section along the right bank of Rangit river). In the slopes having
steep relief, the frequencies of rock/debris fall are more than to slides, whereas

field
observation clearly indicated that proximal to epicentral region, frequencies of both
rock fall and rock slides are much higher than the debris/soil slides and the same are
more concentrated towards the crest of steep ridges. Recent field observation of the

Fig. 1.4 Cracks and subsidence, Nathula-Gangtok Road, Sikkim-Darjiling Himalaya (Source
GSI, Engineering Division, Gangtok, Sikkim)

Fig. 1.5 Some fresh landslips after Sikkim Earthquake, 2011 (Source GSI, Engineering Division,
Gangtok)