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[HDS09-06] Landslides induced by the knickpoint migration in the southern and the eastern margins of the Tibetan Plateau.
Keywords:Landslide, Tibetan Plateau, Himalaya, Minjan, Knickpoint
Along the Kaligandaki River, there are two outstanding knickpoints at Kalopani and Talbagar, respectively. The knickpoint at Kalopani is located at the largest landslide dam, which is called Kalopani landslide or Lete landslide. This landslide is inferred to be preceded by buckling deformation of calc gneiss. It is located near the lower margin of the glaciated area, and the slope could have been eroded by a glacier at the foot of the slope. Downstream of the Lete landslide are aligned 4 gigantic landslides, of which the most upstream one is the Talbagar landslide. It occurred on the left bank just downstream of an outstanding knickpoint of the Kali Gandaki River. This knickpoint propagated from downstream forming a slope break 200-400 m high from the riverbed. Talbagar landslide is a rock compound slide and the other three gigantic landslides were of two mica gneiss and occurred on slopes that had been toppled above the slope break.
There are two significant knickpoints along the Minjian River upstream of the Longmenshan fault. The effects of the knickpoint propagation and inner gorge formation on slope stability are dependent on the geometrical relationships between the river and geological structures. When the geological trend is normal or highly oblique to the river axis, landslides generally do not occur, but gigantic catastrophic landslides have occurred on one side of the Minjiang valley, which can be attributed to a wedge structure consisting of bedding planes and joints with intersections dipping valleyward and tight folds with hinges plunging valleyward. Diexi landslide, the largest landslide along the Minjian River was a wedge failure induced by this knickpoint migration.