Reactivation dynamics of the Kuwari landslide (Uttarakhand, India) and assessment of LLOF hazard using optical imagery, MT-InSAR and hydrodynamic modelling

The Kuwari landslide, located in the central Himalaya of Uttarakhand, India, is a complex slope failure that has experienced multiple reactivations since 2013. The instability is controlled by steep terrain, proximity to the Main Central Thrust, intense rainfall, and anthropogenic disturbances. Repeated mass wasting has led to the accumulation of debris in the Shambhu River, forming a landslide-dammed lake and creating a potential landslide lake outburst flood (LLOF) hazard. The spatiotemporal evolution of the landslide from 2013 to 2025 was reconstructed using high-resolution optical satellite imagery, multi-temporal InSAR analysis employing the Small Baseline Subset (SBAS) technique on Sentinel-1 data, and detailed field-based geological investigations. Further, the stability of the impounded dam was assessed using stability indices, and LLOF simulation was conducted to determine the extent of inundation in the event of a possible dam breach. Optical image interpretation indicates a retrogressive pattern of failure, with a secondary upslope landslide eventually merging with the primary slide mass, thereby enlarging the failure zone. SBAS time-series results identify four distinct phases of accelerated slope movement, each culminating in slope failure and subsequent formation of a landslide-dammed lake. The impounded lake has expanded progressively, increasing from ~ 500 m in 2017 to ~ 885 m in 2022, and further to ~ 1130 m following the 2024 event. Dam stability evaluation using the Morphological Obstruction Index (MOI) and Hydro-morphological Dam Stability Index (HDSI) categorises the dam as unstable. LLOF simulations using HEC-RAS estimate a peak flow velocity of 15 m/s at the breach location, with overbank flooding extending approximately 6 km downstream to Choting village. These findings underscore the urgent need for continuous monitoring, implementation of an early warning system, and slope stabilisation measures.