Abstract: Two large-scale debris flow hazards broke out in the Chongduipu Basin of Nyalam County in 2002, which were mainly caused by the ice lake break. Through the comparison of the remote sensing images in 2017 and 2001 and data in 1987, it is observed that the area of main ice lakes in the basin has changed greatly in the past 30 years. It is preliminarily analyzed that some ice lakes might break. The results show that the area of Galongcuo has increased by 225% and that of Jialongcuo by 101% in the past 30 years; There is one ice lake in a highest-risk state and one in a high-risk state. According to the analysis of the 1/3 and 1/2 breakout modes of Galongcuo Zhongqi Dike, the breakout discharge is 3954 m3/s and 9340 m3/s, respectively. When the Galongcuo collapses according to the 1/3 mode, after the flood peak reaches the post disaster reconstruction Puluo planned new area of Nyalam County, a 45 m wide site area will be submerged. Once a debris flow is formed, the peak flow will reach 6899 m³·s^-1, the mud depth of the debris flow will reach 13 m, the depth of the submerged site will be doubled, and the submerged area will be expanded by 30%. At the same time, it will cause serious damage to the Zhongni highway bridge at the gully mouth. It is suggested that corresponding prevention and control measures should be taken in the planning area of the gully mouth to reduce the harm of ice lake break debris flow.

Key words: Chongdui Gully, Change of Ice Lake, Break, Hazards