Seven minutes of terror: 3D images reveal how Gyirong mudslide unfolded

China’s Ministry of Natural Resources has released three-dimensional imagery showing the area around Gyirong Port on the Chinese side of the China-Nepal border before and after a major mudslide, offering a detailed view of the disaster’s source, path and impact.

The imagery shows that the mudslide caused extensive damage around Gyirong Port, with buildings, roads and bridges visible in pre-disaster imagery no longer identifiable in post-disaster images.

In an interview with CMG, Binod Dawadi, associate Professor of Tribhuvan University in Nepal, confirmed the mudslide originated on the Nepalese side of the border.

Guo Zhaocheng, director of the geological disaster investigation and monitoring center at the China Aero Geophysical Survey and Remote Sensing Center for Natural Resources, told CMG that the ice-avalanche debris flow traveled downstream along the Donglin Zangbo River before reaching Gyirong Port, where it struck buildings and infrastructure.

Guo said a high-altitude glacier in the upper reaches of the Cuojian River in Nepal collapsed at an elevation of around 5,140 meters. The collapse sent ice and rock debris rushing downhill, scouring and entraining loose deposits along the gully and forming a high-speed debris flow, he added.

The debris flow then entered the Guobaxiaqu River, a boundary river between China and Nepal, before joining the Donglin Zangbo River. It subsequently moved downstream along the river channel and evolved into a large-scale mudslide that struck Gyirong Port and continued toward downstream areas in Nepal.

Before-and-after imagery shows the barrier lake formed following the ice avalanche and mudslide in the Gyirong disaster area. © CMG/CGTN

The disaster is a cascading event: It starts with a high-altitude ice collapse, develops into a debris flow and finally grows into a massive mudslide.

Guo said the drastic elevation difference between the source area and Gyirong Port accounts for the extreme speed of the debris flow.

The source area in the upper Cuojian River sits at about 5,140 meters above sea level, while Gyirong Port is at an elevation of around 1,800 meters, Guo said, adding that the significant elevation difference creates an elevation drop of nearly 3,300 meters over a distance of about 20 kilometers.

Based on available time records, Guo said the glacier collapse began at around 10:52 a.m. on August 26, and video footage showed the mudslide reaching Gyirong Port at around 10:59 a.m.

That means the debris flow traveled nearly 20 kilometers in about seven minutes, with an estimated average speed of around 50 meters per second. Guo noted the speed was extraordinarily high, leaving people almost no time to react.

Beyond its extreme speed, the debris flow also produced a rare phenomenon after slamming into the main river channel at Gyirong: part of the flow traveled upstream against the river current. Analysis of the 3D imagery shows the mudslide flowed nearly 3 kilometers upstream in the Gyirong Zangbo River.

Why is the rescue operation difficult?

Experts said damage to transport infrastructure, steep terrain and vast amounts of debris have severely complicated search and rescue efforts.

The section of National Highway G216 affected by the mudslide has been damaged, making vehicle access to some areas extremely difficult. Rural roads running along the Donglin Zangbo valley downstream from Gyirong Port were also completely washed out, blocking both vehicle and pedestrian access.

The narrow, steep gully terrain provides limited space for deploying rescue personnel and equipment. Meanwhile, the force of the mudslide carried some buildings and infrastructure far downstream, making their locations hard to pinpoint. Thick layers of mud covering the disaster zone also make identification and search work more challenging.

Chen Hongqi, an engineer with the Geological Disaster Technical Guidance Center under the Ministry of Natural Resources, told CMG that the risk of secondary disasters is extremely high. Noting there is a bowl-shaped body of water at the bottom of the ice avalanche source area, Chen said the assessment shows that it covers an area of more than 120,000 square meters, though its depth remains unknown at present.

Moreover, on the right side of the steep ice avalanche cliff, there is a mass of ice and rock with numerous ice cracks, Chen said, adding that unlike rock, ice is not firmly rooted to the ground, making its stability much more difficult to assess and predict.

Rescue efforts intensify as more teams arrive

At about 4:30 p.m. on Friday, the first team of six members from the Xizang Fire and Rescue Corps and the first group of 15 members with a search dog from the Sichuan Fire and Rescue Corps arrived at the disaster-hit port. They were the first professional rescue teams to reach the core rescue area, the National Fire and Rescue Administration said.

As of 10 a.m. on Friday, a total of 681 fire and rescue personnel and 113 vehicles had arrived in the remote mountainous border area, while 6,612 pieces of rescue equipment and logistical supplies had been dispatched to Gyirong Town, the administration noted.

A total of 2,096 personnel from local military units, the armed police, fire and rescue services, public security authorities, medical teams and other rescue forces have been mobilized for disaster relief.

More than 300 vehicles have been deployed for emergency rescue, while drones have been used for search and rescue, crowd management and disaster assessment. Two satellite communications vehicles equipped with portable digital trunking base stations and portable satellite base stations have also been deployed to ensure uninterrupted emergency communications on the front lines.

As of 9 a.m. on Friday, a total of 1,386 emergency responders and more than 570 sets of rescue equipment had arrived at the scene to carry out tasks such as search and rescue, risk monitoring, communications support and road clearance, according to the Ministry of Emergency Management.

In addition, 50 rescuers from social organizations including the Xizang Blue Sky Rescue Team and the Ram Union team from Zhejiang Province are participating in the rescue operation. Eleven drone pilots equipped with seven reconnaissance drones and two heavy-lift drones were also sent to conduct aerial surveys, disaster monitoring and area searches, according to the Ministry of Civil Affairs’ National Disaster Reduction Center of China.

Source: CGTN. This article was originally published by CGTN and is republished with permission.