This research focuses on the role of fold growth and river incision in predisposing time-dependent gravitational deformation in slope-scale rock masses. We analyse the case study of the Loumar landslide affecting the NE flank of the Gavar anticline (Zagros Mts., Iran). The landslide evolution seems related to the fold growth that induced the abandonment of a meandering canyon and generated a new narrow gorge that kinetically released the limestone carapace of the flank. In this regard, we infer that Quaternary tectonic deformation and landscape evolution of the fold prepared the flank to the initiation of a Mass Rock Creep (MRC) driven deformation, that evolved into the Loumar viscosity-driven rockslide presently affecting the slope, as evidenced by remote sensing analyses and field survey. We constrain the chronology of the major events that led to the gravitational deformation, through linear temporal conversion of river longitudinal profiles, geomorphometry and OSL dating. The evolution of the drainage network on the flanks of the antiformal ridge highlights that between 568+330/-165 and 81±38 ka, the fold growth, splitted the major streams flowing perpendicular to the fold axis growth. The tectonic deformation related to the vertical and the lateral growth of the fold towards NW, in association with the propagation of minor folds, likely allowed the initiation of the MRC deformation process, in response to river incision. The MRC process cumulated elasto-plastic strain until 5.52±0.36 ka, when the slope evolved into a failure causing the partial occlusion of the valley and the generation of a pond.

This research focuses on the Loumar deformation which affected the NE slope of the Gavar anticline (Zagros Mts., Iran). The landslide evolution is strictly related to the growth of the fold and to the evolution of the Seymareh river drainage system. In this regard, we infer the Quaternary tectonic and landscape evolution of the fold, as well as the chronology of the events that led to the deformation and following failure, through geomorphometric analyses, as well as field surveying and OSL dating of geomorphic markers. Assuming a block uplift model, the drainage network of Gavar fold recorded 1.3{plus minus}0.1 Myr of tectonic history that describes the lateral propagation of the fold towards NW. According to the inversion history, the formation of a parasitic fold at 0.16 {plus minus} 0.015 Ma led to a meander abandonment in the ancient course of the Seymareh River, thus favoring the kinematic release of a large rock mass along the flank of the fold. The latter allowed the initiation of the deformation, which culminated in a huge rockslide at 5.52{plus minus}0.36 ka, as constrained by the OSL age of sediments deposited upstream in a pond caused by the partial damming of the river. Finally, InSAR techniques were applied by processing 181 satellite Sentinel-1 radar images of the ascending and descending orbit, spanning from 16 May 2016 to 21 November 2019. It has been observed that the rockslide is still moving downslope with a maximum displacement rate of 7.5 mm y-1 in the trench zone.