Deep‐seated gravitational slope deformation at Stubnerkogel and implications for the Tauern Railway (Austria)

Deep‐seated gravitational slope deformations (DSGSDs) are widespread in glacially overdeepened alpine valleys, yet their present‐day kinematics often remain poorly constrained. At the Stubnerkogel in the Gastein Valley (Austria), a large DSGSD was previously delineated based on geomorphological evidence, but quantitative data on its current activity remained limited. This study uses high‐resolution X‐band Interferometric Synthetic Aperture Radar (InSAR) data to reassess ongoing deformation affecting the northeastern flank of the Stubnerkogel and the Tauern Railway corridor. The results reveal a spatially coherent deformation area extending from the upper slope across the railway alignment. Persistent line‐of‐sight deformation rates of up to 10–15 mm/a indicate sustained, predominantly downslope‐directed movement. Comparison with geomorphological mapping shows that the active area is fully contained within the previously mapped DSGSD, indicating continued activity of a long‐lived system rather than a new instability. Pronounced spatial variability and differential deformation rates along the railway – particularly at the Salesengraben bridge – highlight the importance of deformation gradients for infrastructure integrity. Overall, the study demonstrates the capability of InSAR to resolve subtle slope movements (<100 mm/a) in complex terrain and provides a robust basis for risk‐informed management of linear infrastructure intersecting DSGSDs.