THE USE OF HIGH RESOLUTION LIDAR DATA TO QUANTIFY SURFACE DISPLACEMENT AT ACTIVE EARTHFLOWS

The Swift Creek landslide, located on Sumas Mountain in NW Washington, is a large, complex earth slide-earth flow. As it has advanced downslope over the past 70 or more years, the toe has thickened and enlarged as material has accumulated at the base of the slide. Weak, fine-grained serpentinitic sediments and a lack of vegetation reduce the strength of the material on the toe, making it susceptible to secondary transport mechanisms during times of heavy precipitation. Secondary hazards (including sedimentation/downstream flooding and debris flows) have originated from this area in the past. In order to better anticipate the occurrence of these secondary hazards, it is crucial to have a better understanding of the complex kinematics associated with landslide mobility.

In this project, we collected and analyzed data from terrestrial laser scanning (TLS) and airborne LiDAR to record surface displacement and to quantify the volumetric transfer of material. This was accomplished through several survey campaigns and subsequent digital image correlation. Topographical analysis over five years reveals a significant mass-transfer of material to the toe; however, short-term analysis shows that a significant amount of material is removed from the toe during the wettest time of the year. Surface displacement is consistent over the main, forested body but variable over the toe. Surface velocity was measured at 2.4 meters per/year for the main body and ranged from 3.3 m - 39.3 m over the toe.