KATHMANDU: A massive landslide triggered by an avalanche at the headwaters of Ungdilung stream in Gorkha’s Chumnubri Rural Municipality-6 caused destructive flooding in the Budhigandaki River, according to a report by the National Disaster Risk Reduction and Management Authority. The study states the avalanche occurred at 4:20 a.m. on Oct. 11 between Chamar and Syerangi mountains at an altitude of approximately 6,000 meters.
The event involved a massive slide of snow, debris, and rock from an elevation of about 5,500 meters. The landslide, which originated from weak sedimentary rock, affected an area extending 300 meters along both banks of the stream. The authority’s report noted that the landslide generated energy equivalent to a 3.5 magnitude earthquake.
The study found that the flow of the Syer stream was obstructed about an hour before the main flood, causing water to accumulate for 1.5 kilometers. The debris-laden flood first reached Sellery at 4:30 a.m., with the peak surge arriving at 6:30 a.m. Water levels at the Sellery hydropower camp reached between 20 and 25 meters.
The flood exhibited characteristics of a viscous mudflow due to the high soil content in the debris. The disaster destroyed the hydropower camp in Sellery, damaged buildings in Jagat, and impacted concrete bridges over the Soti stream and the Budhigandaki River. Five people are reported missing, and hundreds of physical structures along the riverbanks have been damaged.
