InSAR Insights into the Massive Himalayan Leo Pargil Landslide

In the dynamic landscape of the northwest Indian Himalayas, the Leo Pargil Landslide stands as a monumental example of slope instability. This study marks the first detection of this giant landslide through Interferometric Synthetic Aperture Radar (InSAR) techniques. Spanning an impressive 55 km² and mobilizing approximately 25 km³ of rock material towards the Spiti River at a rate of 80 mm/year, it poses significant risks to several villages, towns, and the NH505 highway located atop and along its path.

Deep-Seated Gravitational Slope Deformations (DSGSDs), such as the Leo Pargil Landslide, are pivotal in shaping mountainous landscapes. These giant landslides significantly influence topographic evolution, particularly in regions marked by rapid rock uplift in steep terrain. Understanding these processes is crucial, given their geological significance and the natural hazards they pose to communities in tectonically active regions. However, their inherent unpredictability, influenced by factors like geology, geomorphology, climate, and seismic activities, makes evaluating landslide dynamics a challenging task.

The Leo Pargil Landslide, bounded by the northeast-trending Leo Pargil Shear Zone (LPSZ) and incorporating several brittle normal faults, is conditioned by at least three geological factors: steep slope terrain, the bedding structure of the rock formation, and deep river incision at the base of the landslide. Our study investigates the factors conditioning the landslide, the driving forces behind it, and its evolution, offering new insights into the underlying mechanisms of failure.

In this study, we utilized Sentinel 1A/B satellites, applying Persistent Scatterer (PS) InSAR processing techniques to analyze the active dynamics of the Leo Pargil landslide. By combining InSAR derived velocity field data with the local geology, geomorphological features of the slope and previously published geochronological data we tried to elucidate the possible mechanisms involved in the initiation and development this landslide.

The findings underscore the role of dome exhumation as a geomechanical driver of slope dynamics. The transition in stress fields, tectonic and structural influences, and the interplay between erosion, river incision, and monsoon precipitation anomalies are highlighted as significant factors in the landslide's development. This comprehensive understanding is vital for slope stability assessments and risk mitigation strategies in the Himalayan region.

In conclusion, the study links geomechanical, geochronological, and geomorphological analyses to unravel the complexities of the Leo Pargil Landslide. It emphasizes the significance of the Leo Pargil Dome, not merely as a backdrop but as an active contributor to landslide dynamics, highlighting the critical need to consider both local and broader tectonic contexts in understanding slope instability