A discussion of recent and historic landslides in Vermont, detailing hazards, processes, and slop movement in numerous soil and rock types.

Landslides are instrumental drivers of geomorphological change and can cause costly property damage and threaten community safety. The quantitative impact of slope failure on differing spatial and temporal scales on the landscape remains poorly constrained. Here, we evaluate geomorphological change at one of Vermont's largest documented landslides located in Waterbury, Vermont. The Cotton Brook landslide initially failed in 2019 and mobilized large volumes of sediment downstream toward the Waterbury Reservoir. This study spans from 2014 to 2023 and integrates field-based and remotely sensed data to 1) identify active erosive mechanisms following the 2019 event and 2) develop a workflow that allows us to estimate quantitative topographic change linked to distinct geologic processes. Geomorphological field surveys allowed us to map active landscape change mechanisms and ground truth geospatial data analysis results at Cotton Brook. LiDAR data were processed and analyzed using ArcGIS Pro, Agisoft Metashape Pro and CloudCompare softwares to apply topographic differencing techniques to digital elevation models (DEM) and 3-dimensional point clouds. We develop a workflow and use it to compare the change detection outcomes from each software package to quantify uncertainty. Vertical change measurements derived from models across all techniques ranged from -16.59 m to 16.37 m. Estimates derived from DEMs exceeded point cloud results by up to ~15%. We interpret this discrepancy as an overestimation of change by propagated alignment and interpolation error. Calculated vertical uncertainties are influenced by alignment registration errors and range from ~0 cm to 1.5 m. Elevation change measurements were used to extract sediment volume estimates attributed to landslide features. For instance, our results suggest that up to 123,279.8 m3 of debris material has been deposited at the toe of the landslide. Our approach allowed us to identify how different mechanisms of landscape change contributed to the volumes of erosion and deposition on and around the landslide. An integration of field observations with topographic change modeling results suggest that there are heterogeneous processes influencing mass wasting in our study region including erosional features, which have formed since the 2019 landslide and others that are operating throughout the study region. Notable processes include the collapse of thick units of glacial material bordering the main slip region, gully erosion, and rapid stream bank erosion. The findings of this multi-disciplinary research provide an opportunity to quantify the impact of distinctive geomorphological processes and can help to inform future landslide hazard reduction strategies in the Vermont community.