GYIRONG, Xizang, Aug. 30 (Xinhua) -- An ice-rock avalanche originating from a high-mountain glacier in Nepal has been identified as the cause of a devastating mudslide that struck Gyirong Port in southwest China's Xizang Autonomous Region on Aug. 26, local authorities said Sunday.
A glacier on the north slope of Mount Langtang Lirung in Nepal fractured at an altitude of about 5,200 meters, triggering an ice-rock avalanche, according to a press conference held by the information office of the regional government.
The avalanche plunged rapidly to an altitude of around 4,000 meters, scouring the mountainside and developing into a massive debris flow, which surged about 22 kilometers before reaching Gyirong Port at an altitude of around 1,800 meters.
The disaster flattened an area of about 0.7 square kilometers, destroying 27 buildings and related facilities in the area.
The findings were made by a cryosphere emergency disaster response team from the Institute of Mountain Hazards and Environment under the Chinese Academy of Sciences, based on the analysis of remote-sensing monitoring data and field-transmitted data, as well as on-site surveys and investigations.
The deadly mudslide had claimed 16 lives and left 546 others missing at Gyirong Port as of 6 p.m. Saturday, the regional government said on Sunday morning.
Su Pengcheng, a researcher with the institute, said the disaster is the result of glacier instability under the long-term effects of climate warming.
A post-disaster investigation found that the narrow valley and steep vertical drop in the area where the ice-rock avalanche occurred gave the collapsing mass enormous potential energy. As it descended rapidly, friction and impacts generated large amounts of heat and meltwater.
The resulting mixture swept up moraine and other loose material along the valley and rapidly developed into a debris flow. It reached Gyirong Port at around 10:59 a.m. on Aug. 26, only six to seven minutes after the initial collapse, Su said.
The debris flow caused blockage and backwater near the port before continuing downstream into Nepal.
Su said the disaster was marked by its sudden onset, large peak flow, high speed, strong destructive force and wide impact area, characteristics that he described as a notable new feature of cryospheric disasters on and around the Qinghai-Tibet Plateau.
Meanwhile, a barrier dam above the core area of Gyirong Port is currently stable and unlikely to suffer a sudden complete breach, according to the press conference.
Radar monitoring showed that the dam has an average height of 60 meters and a length of about 1,100 meters. The lake behind it covers about 0.1 square kilometers and has a storage capacity of around 2.2 million cubic meters.
Authorities said that the dam has begun discharging water through overflow and is generally stable.
Rescue operations remain difficult because of the high-altitude terrain, steep valleys and volatile weather, while the surrounding area still faces potential risks from glaciers, glacial lakes and geological hazards, Su said.
So far, a total of 2,141 personnel have joined search and rescue operations, including personnel from the People's Liberation Army, the People's Armed Police Force, the China Search and Rescue Team, China Anneng, border defense units and police, according to the press conference.
A total of 269 rescue vehicles and 3,922 sets of rescue equipment have also been dispatched to the front line, where rescue teams have searched an area of 90,000 square meters. ■
