source: Xinhua

On the morning of August 26, a mudslide triggered by a disaster on the Nepalese side caused heavy casualties and left people missing at the Gyirong Port in Gyirong County, Xigaze, Xizang Autonomous Region, China. At around 10:30 a.m., an ice avalanche suddenly occurred in the glacier area at an altitude of more than 5,200 meters in the upper reaches of the Trishuli River in Nepal. The collapsing ice and rock rapidly developed into a high-speed debris flow and then into a mudslide that rushed toward the Gyirong Port in China. The entire process took only about seven minutes, leaving little time for people to react. So how did the disaster unfold This was not an ordinary mudslide, nor was it a glacial lake outburst flood. Rather, it was a cascading process that began with a glacier collapse, developed into a high-speed debris flow and eventually turned into a mudslide, with its destructive force increasing at each stage. The material traveled more than 20 kilometers downstream, scouring and carrying massive amounts of ice, rock and sediment before ultimately hitting the port. 

First comes the collapse of the glacier. Large masses of ice suddenly break away and tumble down from high elevations, carrying enormous energy with them. Then the ice rushes rapidly through steep gullies, scouring and digging into loose material that has accumulated there over the years, generating a high-speed debris flow. The debris flow continues downstream, picking up river water, mud and sediment along the way. A full-fledged mudslide then forms, eventually surging into Gyirong Port. 

Glaciers are constantly in motion. Once part of a glacier becomes unstable and suddenly collapses from a high elevation, it can quickly develop into a destructive disaster. 

The first is elevation difference. The ice avalanche began at an altitude of about 5,200 meters, while Gyirong Port sits at around 1,830 meters above sea level—a vertical drop of more than 3,000 meters, roughly equivalent to stacking two Mount Tais on top of each other. Such a huge elevation difference means an enormous amount of potential energy can be converted into kinetic energy in an instant. This material did not simply flow downhill—it came crashing down. 

The second is speed. Experts estimate that the debris flow generated by the initial ice avalanche reached speeds of up to 50 meters per second, or about 180 kilometers per hour, roughly as fast as a high-speed train. It took only around seven minutes to travel through the valley for more than 20 kilometers, leaving people virtually no time to react. 

The third is not just water but a “solid wall of debris”. This was not simply water. In an ordinary flood, water makes up most of the flood flow, and once the water recedes, many buildings may remain standing. In a mudslide, however, mud, sand and rocks can account for 15 to 80 percent of the material. It moves like a solid wall made of rock and sediment, burying and sweeping away everything in its path. Roads, bridges and houses could not stop the flow. Instead, they were swept into it, adding to its volume and making the debris mass increasingly powerful. 

The disaster has occurred, but the danger is not over. The mudslide has blocked the river, forming a barrier lake. The unstable terrain also poses a threat to rescue efforts downstream.