Built to last: Long-term stability of steep deglaciated slopes of alpine karst plateaus (Northern Calcareous Alps, Austria)

Steep limestone plateaus of the Northern Calcareous Alps rise abruptly above deeply incised valleys, yet despite their sharp relief, they rarely experience large-scale slope failures. To understand why these massifs remain remarkably stable, we investigated five alpine karst plateaus: Göll, Untersberg, Hagengebirge, Tennengebirge, and Totes Gebirge, using a combination of speleothem geochronology, structural mapping, limit equilibrium analysis and elastic stress modelling. Cave archives reveal a long-lived history of episodic gravitational deformation spanning the last 550 ka. Individual slip events remained small (<40 cm) and did not evolve into continuous rupture surfaces, even though the region experienced repeated glaciations and intermittent tectonic reactivation along the Königssee–Lammertal–Traunsee and Lammertal fault systems. Both stress modelling and structural data show that near-surface deformation is governed mostly by gravitational loading and steep topography, whereas far-field tectonic stresses prevail in the deeper parts of the massifs, with the greatest disturbances in the ridges and edge of the plateaus. Limit equilibrium analyses further demonstrate that the thick-bedded, high-cohesion Dachstein limestones remain stable under dry static conditions, with slip reactivation requiring transient triggers such as seismic loading. Together, these results highlight the stabilizing role of cohesive limestone, the limited persistence of discontinuities, and efficient karst drainage. Even under strong climatic and tectonic perturbations, deep-seated slope deformation in these massifs remained limited in magnitude. This provides new insight into the mechanical resilience of Alpine karst plateaus and constrains the long-term behaviour of carbonate slopes subjected to combined geodynamic and climatic forcing.