3D displacement from shaded relief feature offsets: Multi-decadal deceleration and secondary mini-sliding at the Slumgullion Landslide, Colorado, USA
The Slumgullion landslide in Colorado, USA, is a well-known natural laboratory for studying mass-wasting processes, owing to its ∼4 km length and sustained movement averaging a couple of centimeters per day over the past ∼300 years. However, key questions remain about how its margins and internal boundaries evolve, whether the headscarp still supplies material, and whether motion is accelerating or slowing over decadal timescales. Here we conducted offset tracking on light detection and ranging (LiDAR)-derived shaded relief images to resolve three-dimensional landslide displacements, revealing previously unrecognized secondary mini-slides close to Slumgullion's margins. Comparing our results to those from previous displacement studies revealed the landslide's long-term deceleration of motion since 1939. The secondary failures near the landslide margins and at the headscarp confirm continued material supply to the active slide. The Slumgullion landslide remains structurally dynamic with the maximum shear strain rates at ~1 yr −1 . Despite this activity, toe advance has decelerated by ∼36% since the 1990s. The approach provides a transferable framework for mapping three-dimensional deformation using high-resolution shaded relief images for landslides and other geohazards.