Causes and Damage of the 2020 Periglacial Debris Flows at Zelunglung Catchment in the Eastern Syntaxis of Himalaya

On September 10, 2020, a periglacial debris flow event occurred in the Zelunglung catchment of the eastern syntaxis of Himalaya, Milin County, Tibet. The accident caused serious damage to the Zhibai Bridge and interrupted the traffic. We examined the geological and climatic conditions of this event by remote sensing interpretation and field investigations. The results show that the 9.10 debris flows were triggered by an ice-rock collapse, a comprehensive consequence of previous earthquakes, continuous rainfall, and melt water. The debris flows exhibited the ability of strong erosion and impact. It is estimated that the impact force of the boulders transported by debris flows reached 3.64 × 106 kN. The large volumes of high-position sediment and increasing glacial activity in the Zelunglung catchment provide high possibility for future large-scale debris flows. New engineering countermeasures such as drainage channel or flexible protection layer need to protect the repaired bridge.