Understanding the failure mechanisms of the 2017 Santa Lucía landslide, Patagonian Andes, using remote sensing and 3D numerical modelling techniques

The occurrences of large rock slides often result in catastrophic debris flow within high mountain environments. Discontinuity intersected blocks meeting kinematic conditions stemming from deglaciation-related damage can be triggered by external factors, leading to massive rock slides with a significant downstream hazard. This study presents a comprehensive analysis underlining the mechanism and evolution of the failure during the 2017 Santa Lucía landslide, Patagonian Andes, Chile, utilizing remote sensing and numerical modelling. Due to the remote location, aerial photogrammetry was used to unravel the structural and geomorphological configuration, and four discontinuity sets were identified. Based on colour-shaded relief and slope kinematic analysis, it was found that the failure is governed by combinations of three different discontinuity sets. The failure in the crown portion is complex due to resulting planar and wedge surfaces, whereas in the toe region, the failure is governed by the wedge formation between bedding and other joint set. To further examine its mechanism and evolution, rigid block numerical models were developed in 3DEC to reproduce the failure with real topography and joint parameters. The maximum displacement was observed in the same topographical region where the actual failure occurred, thus conforming to the role of discontinuities in the evolution of the catastrophic failure. Acting on a reduced strength due to rock damage, the modelled slope boosts the instability leading to higher displacements along bonding surfaces with similar attributes as observed in the field. A detailed methodology is discussed regarding coupling remote sensing and 3D numerical modelling for detailed insights into the failure mechanism of the landslides. Overall, our results demonstrate that the Santa Lucía rock slide is a structurally controlled failure where joints provided kinematic freedom, favoured by long-term rock slope damage due to deglaciation.