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.