Landslide catalog for upper Skagit in the North Cascades

Mapped landslides used to evaluate modeled landslide hazard location in Keck et al. 2025, submitted to WRR on 20250125.

Polygons represent the source areas of all active, shallow-pore-water-driven landslides in the model domain. Shallow landslides were mapped from repeat satellite imagery (1998, 2006, 2013 and 2016) draped over a 30-meter DEM in Google Earth (Google Earth, 2023). The image years that were reliably clear enough to make out details like boulders, scarp edges and changes in vegetation and bare areas included 2013 and 2016 images. Image years 1998 and 2006 were not as clear but were good enough to make out changes in vegetation and bare areas.
A landslide was considered active if: (1) it formed or enlarged between photos or; (2) it appeared recent (denuded, and void of any vegetation) and could be traced to a colluvial fan or alluvial fan that exhibited evidence of new deposition. New deposition was identified by changes in color and composition of the colluvial/alluvial deposit between photos. A landslide was considered shallow-pore-water-driven if it formed in convergent topography or slopes where a slight increase in pore water pressure might trigger failure (e.g., slopes exceeding the friction angle of the regolith). Deep seated landslides, which were interpreted as all landslides whose geometry appeared to form independent of the surface topography, and rock fall, which were interpretated as topple like failures and formed deposits of a few boulders, were not mapped.