Debris flow initiation in postglacial terrain: Insights from shallow landslide initiation models and geomorphic mapping in Southeast Alaska

Debris flows pose persistent hazards and shape high-relief landscapes in diverse physiographic settings, but predicting the spatiotemporal occurrence of debris postglacial topography remains challenging. To evaluate flow process terrain, we conducted a geomorphic investigation to characterize geologic, glacial, volcanic, land use contributions landslide initiation across Southeast Alaska. controls on (esp. flow) Sitka, used field observation, mapping, characteristics as documented Tongass National Forest inventory, novel application shallow model SHALSTAB terrain. A complex history glaciation volcanic activity provides template for spatially heterogeneous occurrence. Landslide density region is highly variable, high south- or southeast-facing hillslopes where tephra soils are present and/or timber harvest has occurred since 1900. High along western coast Baranof Kruzof islands coincides with deposition glacial sediment thick exposure extreme rainfall from atmospheric rivers south-facing aspects relative these unclear. Timber also been identified an important control region. Focusing subset geo-referenced landslides near model, which frequently applied non-glacial identify areas potential steep, convergent In validation against mapped polygons, significantly outperformed random guessing, area under curve (AUC) = 0.709 performance classification true positives vs. false positives. This successful demonstrates practical utility analysis mitigate risk people infrastructure.