Tectonic deformation and landscape evolution inducing mass rock creep driven landslides. The Loumar case-study (Zagros Fold and Thrust Belt, Iran)

Several landscape evolution models have been proposed so far to explain the dynamic feedback between Earth surface processes and tectonics in the Zagros Mountains. Nevertheless, the relationship among time-dependent rock mass deformations, landscape evolution rates, and tectonics in triggering large rock landslides is still poorly studied in this region and worldwide. To fill this gap, here we focus on the previously unknown Loumar landslide affecting the NE flank of the Gavar anticline (Zagros Mountains) through a multi-perspective methodology which includes SAR Interferometry, geomorphometry, linear temporal inversion of river profiles and field survey for independent OSL dating of geomorphic markers of landscape evolution. We estimated that at 93 +21/−16 ka the backlimb of the Gavar fault-propagation fold reached limit equilibrium conditions for the slope failure, caused by an acceleration in the fold growth. The growth of a minor fold also induced the abandonment of a meandering canyon and the river migration to a new narrow gorge. The fluvial downcutting kinetically released the limestone strata that started to deform through Mass Rock Creep (MRC). The MRC process accumulated inelastic 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. The obtained creep timespan of 104–105 years since the initiation of the MRC process is consistent with the typical lifespan of gravity-induced slope deformations in non-glaciated regions. For this reason, such an approach can be used for the reconstruction of slow deforming slope evolution to predict the hazard of slopes prone to massive rock slope failure, linking it to the MRC stages.