Causes of large-scale landslides in the Lesser Himalaya of central Nepal |
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| Authors: | Shuichi Hasegawa Ranjan Kumar Dahal Minoru Yamanaka Netra Prakash Bhandary Ryuichi Yatabe Hideki Inagaki |
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| Institution: | (1) Department of Safety Systems Construction Engineering, Faculty of Engineering, Kagawa University, 2217-20, Hayashi-cho, Takamatsu City 761-0396, Japan;(2) Department of Geology, Tribhuvan University, Tri-Chandra Multiple Campus, Ghantaghar, Kathmandu, Nepal;(3) Department of Civil and Environmental Engineering, Graduate School of Science and Engineering, Ehime University, Bunkyo-cho 3, Matsuyama 790-8577, Japan;(4) Kankyo Chishitsu Co. Ltd., Kaizuka, 1-4-5-203, Kawasaki-ku, Kawasaki City Kanagawa, 210-0014, Japan |
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| Abstract: | Geologically and tectonically active Himalayan Range is characterized by highly elevated mountains and deep river valleys.
Because of steep mountain slopes, and dynamic geological conditions, large-scale landslides are very common in Lesser and
Higher Himalayan zones of Nepal Himalaya. Slopes along the major highways of central Nepal namely Prithvi Highway, Narayangadh-Mugling
Road and Tribhuvan Highway are considered in this study of large-scale landslides. Geologically, the highways in consideration
pass through crushed and jointed Kathmandu Nappe affected by numerous faults and folds. The relict large-scale landslides
have been contributing to debris flows and slides along the highways. Most of the slope failures are mainly bechanced in geological
formations consisting phyllite, schist and gneiss. Laboratory test on the soil samples collected from the failure zones and
field investigation suggested significant hydrothermal alteration in the area. The substantial hydrothermal alteration in
the Lesser Himalaya during advancement of the Main Central Thrust (MCT) and thereby clay mineralization in sliding zones of
large-scale landslide are the main causes of large-scale landslides in the highways of central Nepal. This research also suggests
that large-scale landslides are the major cause of slope failure during monsoon in the Lesser Himalaya of Nepal. Similarly,
hydrothermal alteration is also significant in failure zone of the large-scale landslides. For the sustainable road maintenance
in Nepal, it is of utmost importance to study the nature of sliding zones of large-scale landslides along the highways and
their role to cause debris flows and slides during monsoon period. |
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| Keywords: | Himalaya Landslides Clay minerals Hydrothermal alteration |
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