Introduction - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 9

living in northern India, northern Pakistan, Nepal, Bhutan, Tibet and parts of other
Asian nations. Owing to the rugged topography, the complex geological structures,
the fragile soil cover, occurrences of unconsolidated Quaternary sediments along
hill slopes, the high physical weathering, the high intensity monsoon rainfall, the
large temperature variations, and the occurrence of very large magnitude earthquake
events, landslides, debris flows, soil erosion, and other mass wasting processes are
very frequent in this region, which in fact are the primary cause of environmental
degradation in the region. Most of the landslides in the Himalayan region occur
along or very close to major thrust and fault like the Main Boundary Fault (MBF),
the Main Central Thrust (MCT), the Tethyan Thrust (TT), and the Indo-Tsangpo
Suture Zone (ITSZ) where rocks are heavily crushed due to regular tectonic activity
(Fig. 1.1 ). The region comprises lithological groups of Quaternary sediments,
Siwaliks, Lesser Himalayan Sequence, Greater Himalayan Sequence, Leucogra-
nites, Chekha Formation and Tethyan Sediments from south to north. There are six
thrust planes passing parallel to Himalayan range that have made the region most
vulnerable to landslips.
Himalayan Region can be grouped into four major sections with respect to the
distribution of landslides: i. Jammu and Kashmir Region ii. Himachal Pradesh
Region iii. Uttaranchal Region and iv. North-Eastern Region (Fig. 1.2 ). Major
landslide of Jammu and Kashmir region are Khuni Nala Slide (Before 1947), Nashri
Slide (1953) and Sansara Slide (1972). In Himachal Pradesh region, Malling slide
(1980, 1990), Ropagad Slide (1990), Thangi Slide (1985), Telangi Slide (1975),
Sapni Slide (1989) and Urni Rock Fall (1992) are well known landslide sectors.
Kaliasaur Slide (1969), Nandprayag Slide (1970), Patalganga Slide (1970), Debidhar
Slide (1979), Banswara Slide (1998), Bhiri Slide (1982), Guptkashi Slide (1984),
Barua-Bhenti Slide (1998) are the major landslide locations of Uttranchal Region
in Alakananda Valley (Fig. 1.3 ). In Uttaranchal, steep mountain slope, passing of
major thrust plane and existence of weak lithology promotes landslide activities.
Fig. 1.1 Lithology and various thrust plane passing through himalayan range (Source www.iisc.
ernet.in )