Failure Causes and Kinematics of a Catastrophic Red-Bed Rock Avalanche in Zhenxiong, Yunnan, Southwestern China

At approximately 05:51 on 22 January 2024, a catastrophic red-bed rock avalanche with a volume of 16 × 104 m3 occurred in Zhenxiong County, Yunnan Province, southwestern China (105°00′47″ E, 27°28′54″ N). The detached rock mass buried 18 houses, killed 44 people, and caused economic losses of 145 million CNY (23.1 million USD). Field investigations, unmanned aerial vehicle (UAV) imagery, interferometric synthetic aperture radar (InSAR) analysis, and two-dimensional discrete-element modelling using PFC2D were conducted to examine the deformation characteristics, failure causes, and kinematics of the rock avalanche. The results show that internal factors, including high-relief terrain resulting from tectonic activity, fractured rock masses caused by joint cutting and weathering, and a soft–hard interbedded stratigraphic structure associated with argillaceous interlayers, were primarily responsible for the failure. Frost heaving may have been an important triggering factor for the Liangshuicun rock avalanche. Continued attention should be paid to slopes around the rock-avalanche site because ground deformation is still ongoing and may lead to future catastrophic events. The numerical simulation reveals that the kinematic process of the rock avalanche from initiation to final deposition lasted approximately 30 s. About 20 s after failure, the rock debris reached the village, burying houses and killing residents. The maximum velocity and displacement of the rock debris were 45 m/s and 335 m, respectively. These findings provide insight into the instability mechanisms and risk assessment of red-bed rock avalanches in the study area.