Analysis of the May 2019 Joffre Peak landslides, British Columbia, Canada: The importance of considering changes in slope kinematics

This work presents a workflow to investigate the evolution of slope kinematics during the detachment of multi-stage rockslides, using the 2019 Joffre Peak landslide (Canada) as a case study. The Joffre Peak failure developed through multiple temporally and kinematically connected stages, in which successive events progressively modified slope geometry, boundary conditions, and failure mechanisms. Particular attention is devoted to reconstructing how slope morphology and kinematics evolved throughout the different failure stages. The proposed approach combines remote sensing, structural analysis, and discontinuous numerical modelling, supported by high-resolution point clouds for multi-scale characterization of the rock slope. At the slope scale, three main lineament trends were identified through GIS-based analysis, while at the outcrop scale seven discontinuity sets were characterized using a window-mapping technique. Results indicate that high-persistence discontinuities controlled the rear and lateral release surfaces of the landslide blocks, whereas the basal sliding surface, buried beneath debris deposits, can only be constrained through multi-temporal kinematic reconstruction. Two kinematic scenarios are proposed to explain landslide evolution. The first involves sliding along a slope-dipping discontinuity, whereas the second suggests that the later failure stage evolved toward a wedge-sliding mechanism induced by progressive geometrical changes after the initial collapse. Discontinuous 3D numerical modelling demonstrates that both scenarios are kinematically feasible and highlights the strong structural and mechanical interaction between successive landslide stages. Although a unique failure mechanism cannot be conclusively identified, the study demonstrates that accounting for evolving slope kinematics is essential for reliable geomorphic interpretation and rock slope stability assessment in multi-stage landslides.