Said Mukhtar Ahmad, Nitheshnirmal Sadhasivam, Mona Lisa, Luigi Lombardo , Mustafa Kemal Emil, Islam Fadel, Cees J. van Westen , Amira Ahmed, Hakan Tanyas

Understanding the cascading effects of glacier melting in terms of large slope deformation in high mountainous areas could come from the use of Interferometric Synthetic Aperture Radar (InSAR) techniques. In this work, we investigate a slow moving, extremely large landslide (~20 km2) in the Chitral region in Northern Pakistan, which threatens several villages. Our InSAR analyses, using Sentinel-1 data which span a period of six years, allowed us to retrieve the spatio-temporal pattern of downslope deformation for both ascending and descending orbits. The results highlight a worrying situation where the crown of the landslide is moving relatively fast (from 36 to 80 mm/yr). Several sackung-type of movements and other signs of instability were observed in many locations over the crown. As for the toe of the large landslide, a western sliding sector offers a different mechanism than its eastern counterpart where the deformation appears to accumulate through time. This brief description has two implications. One from the most practical perspective, as it calls for further studies and attention from local administrations. And, it also scientifically highlights the strength of InSAR when it comes to unveiling slow deformation regimes, which may be invisible through the eye of other techniques, although they may still lead to catastrophic failures. Such considerations can be even framed beyond the scale explored in this manuscript. In ither words, the same mechanism and threat to local communities can be present across the whole Hindukush-Himalayan-Karakoram range, where glaciers are widely receding due to climate change.