The use of terrestrial laser scanning for the characterization of a cliff-talus system in the Thompson River Valley, British Columbia, Canada

Abstract

A postglacial river terrace along the Thompson River in Interior British Columbia, Canada has been monitored using terrestrial laser scanning (TLS) and high-resolution photography for almost a 3-year study to observe the deformation and failure processes, which result in changes in the slope morphology. Change detection using Multiscale Model to Model Cloud Comparison (M3C2) and a multi-scale dimensionality analysis (CANUPO) were performed on the 3-dimensional point cloud data to track the deposition patterns occurring in this active cliff talus system. Changes documented in the analysis of TLS data were verified using the high-resolution photography. Over 1.5 m of valley parallel retreat was captured in a section of the cliff face related to instability of a cobble and boulder horizon beneath a thick fluvial gravel unit. Because of the high-resolution remote sensing data, it was possible to observe a longitudinal sorting of grain sizes (i.e. fall sorting) in this cliff-talus system, whereby the size of individual particles controls the position on the slope. The overall mapped distribution of particle sizes on the slope remained constant for the almost 3-year study period. Flows of granular debris were observed in TLS change detection and the CANUPO analysis was able to display the longitudinal and lateral sorting of grain sizes that occurs during flow. This case history demonstrates that high resolution remote sensing data of large slopes permits us to link the geomorphic processes occurring in the cliff face with mass movement and deposition occurring on the talus slope below.