A NEW ADVANCE IN ASSESSING LANDSLIDE MOTION USING REPEAT LIDAR POINT CLOUDS

Portions of the ~1300 year old Slumgullion Landslide, located in Southwestern Colorado, continue to move at rates of a few centimeters to meters per year. Movement following the initial failure is common to many large landslides. While not as hazardous to society, slow movements can result in periodic damages to infrastructure. Analysis of these movements can also provide important information to understanding the potential for large-scale remobilization of sections of the slide. A key to monitoring, quantifying, and analyzing internal landslide movement is the acquisition of rates and directions of movement. Here, we present a methodology for capturing surface motion using high-definition Terrestrial Laser Scanning (TLS) targets emplaced on two actively moving sections of the Slumgullion Landslide. The method represents a novel approach to capturing rates of movement. Three repeated TLS campaigns over an approximate 1 year time period (July 2011 - July 2012) indicate the amount of downslope movement ranges between 2.17 m and 3.40 m for one site and 2.94 m to 3.66 m for the second site. The values established from the TLS targets are corroborated with 3D models of standing and fallen trees. The 3D models of the tree trunks are established directly from the TLS point clouds. Statistical analyses show no significant difference between the tree and target results. The 3D modeled tree data also enhances the spatial coverage of the targets providing a greater understanding of the variability in motion across the portions of the slide. The combination of targets and 3D modeled trees permits a more comprehensive coverage of the surfaces; especially given large portions of the slide do not contain trees. We present detailed maps of the topography and surface motions of these portions of the landslide. Our work provides a marked improvement in accurately quantifying the spatial variability of landslide motion and provides the potential to link this information with other geophysical data to allow for a more holistic understanding of landslide motion.