It was not an earthquake, but an avalanche that caused a devastating flash flood in Nepal's Bhotekoshi River. The United States Geological Survey (USGS) clarified this on Wednesday night, and satellite imagery later confirmed the statement. It was observed that a section of the glacier near Langtang Lirung, one of the Himalayan mountain peaks, had descended.
A portion of the glacier broke off at an altitude of 5,127 meters. After rolling down the slope for a considerable distance, snow and mud fell from a height of several hundred meters into the narrow valley between the two mountains. Then, the torrent of snow, mud, and rocks began to move downwards along the mountain slope. Guo Xiaochen, one of the Chinese government's geologists, stated that the torrent of snow, mud, and rocks traveled a distance of 50 meters (165 feet) per second. In this way, an area of about 20 kilometers was virtually devastated in the blink of an eye by the torrent of snow, mud, and rocks. Because the disaster struck in such a short time, ordinary people could not understand what was happening.
Analysis of satellite images shows that the torrent of snow, mud, and rocks descended the mountain slope and merged into the Lende Khola River. This river flows through the border area of Nepal and China. Following the course of the Lende Khola, the mud and rock torrent reached near the Gyirong port in Tibet. The torrent of mud and rocks overflowed both banks of the river, destroying houses, roads, hydroelectric plants, and settlements as it advanced.
The mud and rock torrent descended 100 kilometers down the courses of the Bhotekoshi and Trishuli rivers, nearly to the Nepal-India border. The glacier had broken at an altitude of 5,200 meters. The mud and rock torrent descended ,4500 meters.
The city of Timure in Nepal is located 23 kilometers away from the collapsed glacier. Just before this city, the Bhotekoshi River merges into the Trishuli River. Following this path, the mud and rock torrent reached Syaprubesi, which is 5 kilometers away. Then advancing a bit further from there, it reached Hakubesi. The brownish muddy water was then floating with broken pieces of furniture, dry tree branches, broken asbestos of houses, gas cylinders, etc.
The mud and rock torrent did not stop there. It advanced at a ferocious speed towards Betrawati, located 65 kilometers away from the glacier. From there, it reached Trishuli Bazaar. Even then, the locals knew nothing about this flash flood. Yet, the mud and rock torrent was coming down at a monstrous speed, destroying bridges and settlements. A recently circulated video shows the mud and rock torrent crashing into Trishuli Bazaar. People crowded in shops and markets were trying to escape at high speed. And right behind them, the brown-colored mud and rock torrent was covering the entire area.
Coming down further along the lower basin, this torrent reached Devighat. However, its speed had decreased somewhat by then, and more debris had accumulated in it. Then, this mud and rock torrent stopped at Koltarpur, 100 kilometers away from the glacier.
Nepal's International Center for Integrated Mountain Development reported that a huge amount of melted snow, large boulders, and mud had accumulated in the Bhotekoshi and Trishuli rivers due to the flash flood. As a result, the water level in those two rivers began to rise rapidly. In the Galchhi area, the river water level rose by 9 meters within just half an hour. Overflowing the river banks, everything in the basin area—houses, shops—was washed away in a moment.
On Wednesday night, the American geological observatory stated that the initial geological vibration that was thought to be an earthquake was actually a glacial avalanche. The US agency claimed that the disaster occurred as the glacier descended towards the river basin carrying a mass of mud. The USGS stated that no earthquake occurred on the Nepal-Tibet border at 8:37 AM on Wednesday (local time). The event that was thought to be a 4.4 magnitude earthquake was actually a glacial avalanche and the resulting mudflow. Some geoscientists had stated after initial observations that the flow of the river was blocked by piles of rocks and ice due to the avalanche. That 'blockade' suddenly broke under the pressure of accumulated water, creating the flash flood.
