Explainer: Why is the Gyirong mudslide so sudden and destructive?

A powerful mudslide struck Gyirong County in southwest China's Xizang Autonomous Region on Wednesday. Experts say a combination of extreme terrain, a massive volume of material and the sudden nature of the triggering event made the disaster particularly destructive.

Gyirong County, administered by the city of Xigaze, lies on the southern slopes of the Himalayas, facing Nepal across the Donglin Zangbo River.

Xu Qiang, president of Chengdu University of Technology and chief scientist at the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, said several factors contributed to the mudslide's sudden onset and destructive power.

The first was the enormous elevation difference and steep terrain. The mountain behind the affected area rises to 6,781 meters, while the source area of the ice and rock avalanche is estimated to be at an altitude of around 5,000 meters. Gyirong Port, by comparison, sits at about 1,830 meters above sea level. The elevation difference of several thousand meters and the steep slopes allowed the mass of ice, rocks and sediment to rapidly gain speed as it moved downhill. Once transformed into a mudslide, it traveled with tremendous force.

The second factor was the huge volume of material involved. While an exact figure has yet to be determined, Xu said the volume of material could reach tens of millions of cubic meters, providing an enormous source for the mudslide.

A third factor was the area's high exposure to the disaster. Many homes are located along the path of the mudslide, and the affected area is near the confluence of three rivers, making it particularly vulnerable to the destructive force of the rapidly moving material.

The fourth factor was the sudden nature of the ice and rock avalanche that triggered the disaster. Unlike mudslides triggered by heavy rainfall and gradually supplied with water and loose material, an ice and rock avalanche can occur abruptly. Once the collapsing mass enters a valley or river system, ice, rock and sediment can be rapidly transported downstream and develop into a powerful mudslide.

Together, these factors made the disaster exceptionally destructive, Xu said. A preliminary estimate, based on an average affected width of 200 meters, puts the affected area at around 15 to 20 square kilometers.

Rescue faces risks from secondary disasters

Experts analyzing imagery of the affected area said the region's topographic and hydrological conditions are highly complex.

The disaster occurred near the junction of a main valley and a tributary, where the elevation difference exceeds 3,000 meters. Glaciers and glacial lakes are also located in the upper reaches.

These conditions have created significant challenges for rescue efforts.

One major uncertainty is the stability of the damaged mountain slope at the source area, which could pose a risk of secondary disasters. Water conditions in the upper reaches of both the main valley and tributaries also remain unclear.

Rainfall is another key concern. The area consists of high mountains, narrow valleys and concentrated water flows, meaning further rainfall could affect the stability of the disaster zone.

The narrow terrain also makes access difficult. Roads leading into and out of the affected area face potential threats from mountain collapses, landslides and falling rocks.

Hu Jiaojiao, a glaciology researcher and chair of the Tianjin Extreme Climate Change Response Promotion Center, said experts are continuing to monitor weather conditions and assess the risks of further scouring and geological instability.

The region also contains several sub-basins with major elevation differences, she said. It remains unclear whether additional ice and rock avalanches or mudslides could occur. Where rivers and tributaries are present, they can rapidly transport ice, rock and sediment downstream along valleys.

For rescue workers, the first challenge is the instability of the post-disaster natural environment. The second is operating at high altitude and under harsh conditions.

With limited personnel and resources, organizing effective search, rescue and evacuation operations in such an extreme environment remains a major challenge.