Work

Recent satellite-based radar and optical monitoring of the activity of retrogressive slow-moving landslides in Nepal during monsoon

Year: 2026

Type: article

Abstract: The steep Himalayan slopes are highly susceptible to landslides, primarily triggered by earthquakes and intense monsoon precipitation. Along the southern flank of the Himalayas, a specific type of landslide affects old, destabilized hillslopes characterized by intense internal fracturing and prone to rapid retrogressive erosion through deep gully incision, ultimately leading to the catastrophic collapse of secondary slides. Understanding these mechanisms requires identifying potential spatiotemporal relationships between landslide units and triggering factors such as rainfall, increased groundwater pressure, and gully erosion. In this study, high-resolution optical and radar satellite remote sensing data were integrated to characterize the dynamics of three retrogressive, slow-moving landslides located in the Marsyangdi and Khudi valleys of central Nepal. The combination of digital surface model (DSM) differencing and optical pixel-tracking from very high resolution Pléiades imagery provides a comprehensive view of the three-dimensional surface displacement fields across the landslides, offers insights into their internal kinematics, and highlights how gully downcutting drives landslide activity through basal destabilization. Our dataset also demonstrates that high-temporal-resolution displacement measurements derived from SAR amplitude imagery enable tracking of landslide dynamics during slow- to moderate-activity phases (displacement > = 0.5 m). In the specific case of the retrogressive landslides studied here in central Nepal, we identify various nonlinear responses to changes in groundwater table level: either involving strain hardening effects, or early destabilization of a lower unit followed by large displacements in the main landslide body.

Source: Geomorphology

DOI: 10.1016/j.geomorph.2026.110561

Authors: Florian Leder, Simon Daout, Jérôme Lavé, Pascal Lacroix, Nicolas d’Oreye de Lantremange