Anthropogenically accelerated mass movement, Kulu Valley, Himachal Pradesh, India

Abstract

A devastating landslide occurred on 12 September 1995 near Luggar Bhatti, Kulu, Himachal Pradesh, and killed 65 people. An estimated 0.96×10 6 m 3 of unconsolidated mass slid SSE down the terminal part of a thick alluvial fan of Quaternary age on the left bank of the Beas River. About 0.03×10 6 m 3 of dislodged material formed a 15-m high and 150-m long hump at the bottom of the failed slope; a shallow sag pond developed in the rear. The slide occurred after heavy rains on 3–6 September in the region when the Beas rose to a bankfull position. Factors involved in this toppling-cum-debris slide include steep slope, continuous seepage with high pore water pressure in unconsolidated material, a road-cut obliterating the foot of the fan slope, and impinging by the Beas River during the flood. A survey in the area showed that a variety of mass movement processes were triggered by the heavy rains in September; the most predominant being a series of slope failures on the outside of meander loops and bank erosion caused by turbulence of the overflowing Beas River. Extensive damage was sustained by National Highway-21 (NH-21), a bridge ramp near Bhuntar, a suspension bridge at Kulu and two other bridges upstream. Most damage occurred in the Manali area where massive buildings were washed away by the flash flood. This paper examines the factors and processes responsible for triggering widespread mass movement and related damages in the Kulu Valley. Whereas some smaller events occurred in the early and middle part of this century, the recurrence and intensity of mass movements are recent phenomena attributed mainly to escalating socio-economic development, growth of tourism, and population pressure. Some long term policy is suggested for mitigation of landslides and other denudational processes in relation to impelling human factors.