Bhotekoshi flood reveals the growing danger of Himalayan cascading hazards

The catastrophic flood which took place in the Bhote Koshi–Trishuli river area in August 26 has left Nepal facing one of the worst mountain disasters in recent times. Starting in the glacierized Himalayan region, the situation quickly turned into a destructive sequence involving ice, rock, debris and water, which moved downstream through Rasuwa and then into Nuwakot, Dhading, Gorkha, Chitwan, Tanahun and Nawalparasi. As a result of the disaster, settlements, bridges, roads, hydropower facilities and the Rasuwagadhi–Kerung trade route were destroyed, together with a huge loss of human life and livelihoods.

The incident was caused by a major failure of an ice-and-rock mass in the upper Lhende Khola catchment, north of the Langtang-Lirung peak. Analysis using satellite data indicates that an area of about 2.10 square kilometres of glacier and the surrounding land from 5,200 m elevation have collapsed, with an additional 3.05 square kilometres being greatly eroded at an elevation of about 3,800 m, part of which is debris-covered glacier. The total estimated volume of ice, rock, sediment and debris that was moved could have exceeded 74.43 million cubic metres, though these figures need to be confirmed by further studies.