Hillslope-mobilizing movements are critical to hazard engineering and landscape evolution. Deep-seated gravitational slope deformations (DSGSDs) can persist undetected for decades before transitioning into catastrophic failures. Despite their global prevalence, DSGSDs are underdocumented in the tectonically active and disaster-prone Himalayan belt, necessitating investigation of their climate-tectonic and hydro-lithological controls over long geomorphic timescales. This study investigates the Shiala Landslide Complex (SLC), which is identified as a DSGSD system encompassing an entire north-facing hillslope, in the southeastern Kumaun Himalaya (SKH). To understand the mechanism of SLC, we implemented an interdisciplinary approach combining geological and landslide field mapping, Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR), geotechnical analysis, and runout modeling using the Rapid Mass Movement Simulation- Debris Flow (RAMMS-DF) module. Key observations include the following: (i) progressive slope enlargement with ~58 m headscarp retreat between 2013 and 2025, including 14 m between 2023 and 2025 correlating with seasonal rainfall; (ii) displacement rates (vertical: −7.10 to +5.61 mm/yr; horizontal: −6.25 to +10.35 mm/yr) indicating rotational movement with headscarp subsidence, toe uplift, and lateral spreading, all seasonally accelerated during monsoon; (iii) strong structural control of the Main Boundary Thrust (MBT), Lugad Thrust, and transverse faults influencing lithological boundaries and flow dynamics; and (iv) consistent runout deposition in the lower transportation zone, terminating before the Ladhiya River also reflecting the concavity of the SLC body, with larger-volume events showing faster runout but lower erosional efficiency (0.49%) compared to smaller flows (11.33%). These findings provide critical insights into DSGSD behavior in active orogenic terrains and establish a baseline for regional hazard mitigation and risk management.
Solanki et al. (Mon,) studied this question.