The largest and fastest slow-moving landslides can cause substantial hazard to infrastructure and communities. Nevertheless, assessing the thickness, mechanical state, and displacement rate of such landslides is very difficult.
Handwerger et al.  use radar measurements obtained from an Uninhabited Aerial Vehicle to measure the 3D velocity over more than a hundred landslides in Northern California. Further, they used the displacement pattern to infer the landslide thickness and strength.
They found that these slow landslides had geometries similar to rapidly failing landslides, and also that beyond a certain size, large landslides seemed to grow only in area and not grow thicker. Last, and more puzzling, they found that larger landslides are weaker. To explain this, the authors propose that larger landslides have more chance to incorporate the very weak portion of the heterogeneous local lithology.
Citation: Handwerger, A. L., Booth, A. M., Huang, M.‐H., & Fielding, E. J. . Inferring the subsurface geometry and strength of slow‐moving landslides using 3‐D velocity measurements from the NASA/JPL UAVSAR. Journal of Geophysical Research: Earth Surface, 126, e2020JF005898. https://doi.org/10.1029/2020JF005898
—Odin Marc, Associate Editor, JGR: Earth Surface