APPLICATION OF TLS IN GROUND SURFACE DEFORMATION MONITORING AT KEKAWAKA LANDSLIDE OBSERVATORY IN NORTHERN CALIFORNIA

Landslide failure speeds vary from catastrophically rapid, to movement imperceptible to the human eye. Some landslides move episodically and reactivate during wet periods, persistent movers may accelerate, but forecasting the timing of these behaviors is problematic. Knowledge of mechanisms responsible for determining landslide timing and speed remains incomplete, rendering forecasting intractable in many cases. A previous study of an episodic, slow-moving translational debris slide in northern California hypothesized that soil swell pressure modulated sliding resistance along parts of the landslide's lateral boundaries and accounted for as much as five months of delayed landslide response relative to forecasted timing based only on variable porewater pressure and landslide mass (Schulz et al., 2018). We seek to further test this hypothesis by evaluating shrink-swell-induced topographic change in the Kekawaka landslide observatory (described by Schulz et al., 2018) using a terrestrial laser scanner (TLS), also referred to as terrestrial LiDAR (Light Detection And Ranging). Our work will be incorporated into a larger study of geology, hydrology, swelling, and movement including three other landslides in the observatory. TLS has been used to rapidly produce accurate and precise topographic data of landforms, and their potential change by scanning repeatedly over time. This makes TLS an ideal tool for digitizing subtle ground swell displacement that may not be recorded by remote sensing techniques or in-situ instrumentation. At the time of this writing, we had performed TLS scanning near the end of the spring 2024 wet season when soils were likely near their most-swollen state; dry-season scanning after soils shrink is planned for late summer 2024.