Insights from finite element modelling and remote sensing on a potential deep-seated slope deformation in a deglaciated valley in the southern Coast Mountains, British Columbia

Large-volume landslides are common processes in high mountain settings, with potential cascading hazards of rock avalanches or debris flows that may reach local communities and infrastructure. Deep-seated gravitational slope deformation is a complex process with signs visible on many slopes in the Mount Meager Volcanic Complex. Fieldwork, remote sensing and numerical modelling were used to better understand the properties and behaviour of a potential gravitational deformation zone in the Mosaic Creek Valley. Fieldwork determined that lineaments with an antislope morphology are located dominantly in the midslope. Synthetic Aperture Radar Interferometric (InSAR) results identified accelerated surface movement during August 2022. Displacement greater than 20 cm over a 12-day period was observed, although there is large uncertainty with the greatest values. Numerical modelling was performed using the finite element method with results suggesting a deep-seated gravitational deformation process, emphasising the importance of in-situ stress and snowmelt. Elevated stresses result in a similar displacement zone as observed in remote sensing data and yielding zones which may contribute to different lineament morphology. The results highlight the complex behaviour of gravitational deformations and the wide range of factors that affect their behaviour, making them critical to consider in future monitoring programs and hazard assessments.