"8·26" debris flow disaster in Jilong, Tibet: Experts analyze ice and rock avalanche chain disaster risks and monitoring challenges

On September 6, the "8·26" Debris Flow Disaster Emergency Rescue Headquarters in Jilong County, Tibet Autonomous Region held a meeting with Chinese and foreign media.

Su Pengcheng, a researcher at the Chengdu Institute of Mountaineering, Chinese Academy of Sciences, answered the questions at the meeting regarding risk monitoring problems such as barrier lakes and ice-rock avalanche-debris flow chain disasters in the Jilong debris flow disaster.

He said that the source of the ice-rock avalanche-mudslide disaster chain is located on the northern slope of Langtangli Mountain Peak in Nepal. The ice-rock avalanche occurred at an altitude of about 5,200 meters and fell rapidly. It washed away the mountain and formed a giant mudslide. It hit the Purepuzangbo and Donglinzangbo expressways for about 22 kilometers and then directly reached the Gyirong Port in my country at an altitude of about 1,800 meters. The whole process only took 6 to 7 minutes, causing extremely serious harm to the downstream.

After being disturbed by this ice-rock collapse-debris flow chain disaster, the channel runoff continues to flow, and a huge amount of loose moraines and collapse deposits remain on the bank slopes and channels. The secondary risk of blocking the lake again and forming a barrier lake exists objectively. The real high risk mainly comes from the blocking of the channel by large-scale ice and rock avalanche disasters on the ditch bank. The threats can be summarized as: medium to high-level secondary risks, mainly local water congestion and small-scale temporary damming. In extreme scenarios, there are real hidden dangers of channel blockage, which mainly threaten the safety of downstream rescue and search and rescue personnel.

Therefore, a thorough investigation of the geological hazards in the Donglin Zangbo watershed was carried out and monitoring and observation was strengthened. Through remote sensing analysis combined with field surveys, it was found that in addition to the barrier lakes that have naturally discharged water, there are currently 26 glaciers larger than 1 square kilometer and 11 glacial lakes larger than 0.1 square kilometers distributed in the basin. Around the distribution of glaciers and glacial lakes in the surrounding areas, multiple industry departments have gathered the strength to carry out continuous remote sensing monitoring. Currently, multiple departments including the Ministry of Emergency Management, the Ministry of Natural Resources, the Ministry of Water Resources, and scientific research institutes are working together, and an expert team is conducting real-time research and judgment to ensure the safety of downstream rescue and search and rescue personnel.

The Geelong Port is located in a high-altitude and remote area on the China-Nepal border. The source area of ​​the ice and rock collapse is extremely cold and hypoxic, making it difficult for manpower to reach. There are observation blind spots in the cross-border watershed. It is difficult to power supply, communicate, and operate and maintain ground detection equipment. The precursors of the ice and rock collapse-debris flow disaster chain are hidden and the warning window is only a few minutes. The traditional single-point monitoring model cannot cover the risk sources in the entire basin. Based on the actual situation of Jilong Port, researcher Su Pengcheng suggested that the following aspects of work can be strengthened in the future:

First, strengthen research on the disaster-causing mechanisms of cryosphere composite disaster chains such as cross-border ice and rock avalanches and debris flows in the Himalayas, and deepen the research, judgment and identification of early warning signals for disaster chains.

The occurrence of ice and rock avalanche disasters in the Himalayas is significantly driven by climate change and responds strongly to climate warming. At the same time, the geological conditions in the region are complex and diverse, and tectonic activities are frequent. Faced with the trend of accelerating the frequency of "rare catastrophes" under the background of climate change, we need to carry out early research and judgment on glacier instability risks, fill in the blind spots in source monitoring, and introduce new geophysical detection technologies to achieve dynamic monitoring of the entire chain, obtain more effective precursor information, and provide strong basic theoretical support for accurately identifying disaster risks. In this way, combined with the risk avoidance plans of residential areas in the lower reaches of the river basin, the accuracy of early warning and forecasting of the disaster chain can be continuously improved.

Second, build an integrated air-space-ground non-contact monitoring system across the Himalayas to reduce reliance on field stations in extremely high-altitude source areas. At present, it is necessary to research and develop equipment adapted to the alpine environment, and form a layered monitoring model of "satellite wide-area (large-scale) screening-encrypted monitoring of key points-downstream disaster alarm", so as to gain evacuation time for the downstream as much as possible.

Third, promote the construction of cross-border scientific research cooperation and early warning coordination mechanisms. The occurrence of the cryosphere compound disaster chain is a natural process that is not restricted by national boundaries. The location of upstream danger sources outside the country is the biggest shortcoming of this monitoring. Rely on some international cooperation platforms to promote data exchange and joint risk assessment with countries in the Himalayas at the basin scale, explore rapid communication channels for cross-border early warning information, and extend the starting point of early warning to the complete river basin upstream and downstream.