Disaster mechanism and evolution of Nagune Gully landslide-debris flow disaster chain in Minxian County, Gansu Province

This paper is the result of geological hazards survey engineering.

Objective Naguni gully is located in the Eryang watershed in Chabu Town, Minxian County, Gansu Province. Structurally, it is situated within the Lintan-Dangchang fault branch zone. It is a small-scale, high-frequency debris flow gully, and the development of landslides within the watershed results in a unique landslide-debris flow disaster chain. The mechanisms and evolutionary processes of this disaster chain are worthy of in-depth study.

Methods Through field investigations, remote sensing interpretation, and laboratory experiments, the development characteristics of the Nagune gully disaster were clarified. The disaster mechanisms of the landslide-debris flow chain were studied, and the evolutionary process of the landslide-debris flow disaster chain under fault activity within the small watershed was analyzed.

Results The research results indicate that the landslide-debris flow disaster chain in Nagune gully manifests as a cyclic development of debris flows, landslides, and burst flood debris flows. The current fault activity results in the development of loose materials and unstable slopes within the channel, establishing the material basis for the formation of the disaster chain. High-frequency, short-duration heavy rainfall or continuous rainfall triggers multiple occurrences of debris flows. The lateral erosion of the gully foot by debris flows causes slope instability and leads to landslides. The landslides block the gully, forming a barrier lake, and the breach of the barrier lake results in burst flood debris flows. The evolutionary process of the disaster chain includes the initial erosion phase of debris flow, gradual deformation of slopes approaching critical instability, the formation of a blocked gully due to landslide movement, breach of the barrier lake leading to burst flood debris flows, erosion of the opposite slope foot causing further instability and downslope movement, and the cyclic development of debris flows, landslides, and burst flood debris flows.

Conclusions In summary, the formation of the disaster chain in Nagune gully is the result of current fault activity and the combined effects of short-duration, concentrated rainfall or continuous rainfall. The repeated occurrence of debris flows during the rainy season and the creeping deformation of landslides within the Nagune watershed contribute to the cyclic development of the landslide-debris flow-burst flood debris flow disaster chain.