Sackung and enigmatic mass movement folds on a structurally-controlled mountain ridge

The recently emerged concept of “slope tectonics” suggests that mass movement processes can produce structures similar in morphological expression to that of extensional, strike-slip and compressional tectonic deformations. Further, there has long been debate about the (tectonic or gravitational) origin of lineaments found on hillslopes. Here we present cases of where geological structure and inherited tectonic structures have preconditioned the development of mass movements and creation of slope tectonic features on a monoclinal ridge (Smrk Mt.) in the Outer Western Carpathians, Czechia. Geomorphic mapping from LiDAR-derived topography, structural measurements, electrical resistivity tomography and ground penetrating radar, were used to map synthetic and antithetic scarps, thrusts, and folds, and assess their relation to geological and tectonic structures. The scarps are found to be strongly related to transverse (NNW to NNE trending) inherited normal and strike-slip faults and mainly cross-cut the topography of the mountain ridge. Some of the folds are thought to have originated from buckling or compression in the distal parts of landslides. In other places, transpressional folds have developed oblique to major lateral shear surfaces interpreted to be sackung (mass movement scarps) that have been inherited from tectonic faults. The transpressional folds developed due to localized contraction along bends in the lateral shear surface as mass movement proceeded. Ramp-flat thrust folds developed in the compressional parts of landslides, where the landslide intersects with slope parallel sackung and/or inherited fault planes inclined to the slope. Altogether, this study demonstrates a connection between kinematics of deep-seated gravitational slope deformations (DSGSDs), shallower landslides and the origin of transpressive, ramp-flat thrust, and detachment structures in rock slopes.