Multitemporal InSAR analysis of long-term creep and active thickness changes in a paleo riverbank landslide driven by anomalous water levels

Riverbank landslide creep is strongly influenced by environmental drivers such as river water level and rainfall, which can modify both surface kinematics reflected by time-varying three-dimensional (3D) deformation and the active thickness of landslides. However, how these changes respond to abrupt river perturbations, such as river-damming events, remains poorly documented. Here, we apply multitemporal Interferometric Synthetic Aperture Radar (InSAR) to investigate the Xiongba paleo-landslide along the Jinsha River, focusing on its response to two upstream river-damming events on 11 October and 3 November 2018. Our results show that the InSAR-derived 3D displacement time series, constrained by the aspect-parallel flow (APF) assumption, strongly agrees with Global Positioning System (GPS) measurements. With periodic components removed, the quasi-3D deformation field combined with mass-conservation inversion and borehole constraints enabled reliable active-thickness estimation. Crucially, staged InSAR monitoring reveals a transition of the Xiongba landslide from slow to accelerated creep, directly driven by anomalous water-level fluctuations. Spatially, deformation reorganized with pronounced acceleration at the right leading edge, where the magnitude of the three-dimensional displacement rate at a representative point increased from 0.045 m/a to 0.177 m/a. The accelerated creep increased the inverted active thickness from 36.8 m and 38.9 m to 48.9 m and 45.8 m at the two borehole locations, respectively, indicating deeper mobilization of the landslide mass. This observational evidence demonstrates that extreme hydrological perturbations can push a slow-moving landslide into an accelerated stage, providing critical insights for interpreting precursory signals and improving proactive early warning along large river valleys.