GEOMORPHIC CHANGE DETETION USING MULTI-TEMPORAL LIDAR DATA OF A DEEP SEATED LANDSLIDE, COAST RANGE, OREGON

Landslide hazard assessment of densely forested, remote, and difficult to access areas can be rapidly accomplished with airborne light detection and ranging (lidar) data. Geomorphic change detection by lidar-derived differential digital elevation models (DEMs) can provide valuable insight to the reactivation process of unstable landslides. The purpose of this study was to evaluate multi-temporal lidar data for geomorphic change of an unstable deep seated landslide. Differential DEMs from biannual (leaf-on and leaf-off) lidar data were calculated to generate a DEM of Difference (DoD) raster to identify and quantify vertical changes in landslide depletion and accumulation zones. The application of a 0.5 meter threshold value was completed to remove potential noise from the differential data. The landslide was instrumented with 20 crack monitors and surveyed with total station and high resolution GPS data. Total station survey points were established perpendicular to the direction of landslide movement to measure horizontal deflection. Soil samples were collected to characterize the landslide mass and used in slope stability modeling. Examination of the accumulation and depletion zones of the landslide terrain did not show anticipated volume changes in these areas. Volume changes detected in the differential lidar data appeared to result from erosion and transport of soil in the exposed head scarp and scarp flanks of the landslide.