Ice-rock avalanche in Nepal triggered deadly mudslide along China-Nepal border, investigation finds

A glacier in Nepal collapsed at an altitude of about 5,200 meters at around 10:52 a.m. on Wednesday, triggering an ice-rock avalanche that developed into a massive mudslide, Su Pengcheng, a researcher at the Institute of Mountain Hazards and Environment under the Chinese Academy of Sciences, said at a press conference on Sunday.

The finding was made by a team from the institute based on an analysis of remote sensing monitoring data, information transmitted from the disaster site and on-site field investigations.

Following the glacier collapse, the ice-rock avalanche rapidly plunged from an altitude of about 5,200 meters to around 4,000 meters, scouring the mountainside and forming a giant debris flow. After traveling about 22 kilometers at high speed, the flow reached Gyirong Port in southwest China's Xizang Autonomous Region, at an altitude of about 1,800 meters. 

The disaster flattened an area of about 0.7 square kilometers, destroying 27 buildings and related facilities.

The event was a cross-border cascading disaster. After the glacier collapsed, the massive flow entrained and scoured loose deposits along the gully, entered the Guobaxiaqu River, a boundary river between China and Nepal, and then flowed westward into the Donglin Zangbo River. It eventually evolved into a highly destructive debris flow that severely damaged Gyirong Port and the downstream areas.

The mudslide's destructive power was driven by the extreme elevation difference and speed. It dropped nearly 3,300 meters in elevation along the 20-kilometer path and took only seven minutes to reach Gyirong Port after the initial glacier collapse, reaching an average speed of about 50 meters per second. The rapid onset left people with almost no time to react or evacuate, resulting in a disaster of catastrophic scale and severe casualties.