NISAR Detected Ground Movement Before Deadly Nepal-Tibet Ice-Rock Avalanche
New analysis of satellite radar data from the NISAR mission – a joint project of NASA and the Indian Space Research Organisation (ISRO) – has revealed significant ground deformation on a Himalayan slope in the weeks before a devastating ice-rock avalanche struck the Nepal-Tibet region in 2026. The findings, shared by Zhejiang Liu, a PhD student at Chang'an University, show that the unstable slope had already been undergoing substantial movement before the ice and rock mass gave way, triggering a destructive flood downstream.
The analysis used Synthetic Aperture Radar (SAR) pixel-offset tracking, a technique that compares radar images taken at different times to measure ground displacement. This allowed researchers to detect multiple metres of cumulative movement concentrated around the precise area from which the avalanche later originated. Three-dimensional visualisations further showed that the deformation was largely confined to the steep upper portion of the mountain slope rather than being spread evenly across the surrounding terrain.
That concentration of motion is particularly significant, according to the researchers, because it suggests stress was building within an unstable section of the slope before its eventual failure. While not every slope that shows deformation will collapse, the findings demonstrate how radar-based monitoring can provide early warning signals in dangerous mountain environments.
The 2026 collapse triggered a destructive flood disaster downstream, affecting communities across parts of Nepal and Tibet. The event underscored how a high-altitude slope failure can quickly transform into a larger hazard as ice, rock, and debris enter river valleys, potentially threatening areas far from the original collapse zone.
The NISAR observations highlight the potential value of frequent satellite radar monitoring in some of the world's most hazardous mountain regions. Unlike optical satellites, radar systems can see through clouds and operate in darkness, making them particularly useful for monitoring the high Himalayas, where persistent cloud cover and extreme terrain often limit conventional imaging.
Experts note that determining whether deformation represents an imminent threat requires repeated observations, geological assessment, and ground-based monitoring where possible. Nevertheless, the NISAR data offer a compelling example of how space-based radar can reveal changes in remote and inaccessible terrain, providing a potential tool for hazard assessment and disaster preparedness.