Quantitative investigation of a Mass Rock Creep deforming slope through A-Din SAR and geomorphometry

A Deep-Seated Gravitational Slope Deformation (DSGSD) affects the SE slope of the Siah-kuh anticline in its SE periclinal tip in the Ilam region (Zagros Mts., Iran), almost 30 km south of the Seymareh Landslide, which represents the largest landslide on Earth surface. The DSGDS is driven by a Mass Rock Creep (MRC) process and involves an area of about 8 km2. The evolution of such a gravity-induced process is strictly related to the evolution of the of Dowairij River drainage system. River incision originated a stress release at the bottom of the slope which likely caused the initiation of the deformational process. The present study is part of a broader International Programme on Landslide project (Project IPL-237) focused on the role of time-dependent rock mass deformations and landscape evolution rates as predisposing factors for massive rock slope failures. In this regard, the preliminary results of an ongoing research are here presented focusing on the assessment of the present-day landscaping processes. Specifically, a geomorphological survey was carried out in this area firstly through the analysis and interpretation of remote data (Google Earth satellite optical images), which led to the first detection of possible gravity-induced landforms, such as evidence of bulging and lateral release within the deforming slope of the Siah-kuh fold-related ridge. To confirm and quantify the existence of ground displacement due to a MRC process, InSAR techniques were performed for the Siah-kuh slope and surrounding areas by processing 279 satellite Sentinel-1 (A and B) radar images of the ascending and descending orbit spanning from 06 October 2014 to 31 March 2019. Moreover, a quantitative morphometric evaluation was also performed through a morphometric index suitable for predicting the catchment-scale suspended sediment yield on the deformation area produced by the Dowairij River system. We derived the erosion rate of the drainage network responsible for the valley engraving which allows to estimate a starting time for MRC in the order of 101 ka. The comparison between the valley erosion rate and the slope strain rate reveals a difference of almost one order of magnitude allowing to assume that the gravity induced process, identified from remote and field geomorphological survey, evolves faster and originates landforms which can be preserved by the drainage system of the Dowairij River.