1.Institute of Geomechanics,Chinese Academy of Geological Sciences;2.Longyan University;3.Chongqing Jiaotong University
the second comprehensive scientific investigation of the Qinghai Tibet Plateau（2019QZKK0902）
【Objective】Nagune gully is a small-scale with high frequency debris flow gully and located in Eryanggou watershed, Chabu Town, Min County, Dingxi City, Gansu Province, and structurally located in the branch fault zone of Lintan-Dangchang fault. The landslide developed in the basin makes the basin produce a special landslide-debris flow disaster chain. The disaster mechanism and evolution process of the disaster chain are worthy of in-depth study. 【Methods】Through field investigation and remote sensing interpretation, combined with laboratory experiments, clarified the development characteristics of disasters in Nagune gully, studied the formation mechanism of disaster chain of landslide-debris flow, and dissected the evolution process of disaster chain of landslide-debris flow under fault activity environment in the small watershed. 【Results】The results show that: The disaster chain of landslide-debris flow in Nagune gully is in the form of reciprocating development of debris flow-landslide-burst flood debris flow. The activity of fault makes the development of loose material source and unstable slope, which lays the geological foundation for the formation of disaster chain, the frequent short-term concentrated rainfall and continuous rain stimulate the occurrence of debris flow, the erosion effect of debris flow on the valley makes the slope unstable and forms landslide, the landslide blocks the valley and then the burst flood debris flow is formed after the barrier lake breaks the dam. The evolution process of landslide-debris flow disaster chain is determined as follows: debris flow formation and erosion gully stage, slope deformation and gradually approaches the critical instability stage, landslide slides down and blocks the channel to form a barrier lake stage, barrier lake burst then forms burst debris flow stage, the slope in the opposite is eroded and slides down stage, the reciprocating development stage of debris flow-landslide-burst flood debris flow stage. 【Conclusions】To sum up, the formation of the disaster chain in Nagune gully is the result of the current fault activity, short-term concentrated rainfall or continuous overcast rain; The continuous occurrence of debris flow and the continuous creep of landslide in annual rainy season lead to the continuous process of debris flow-landslide-burst flood debris flow.