India’s NASA-ISRO Synthetic Aperture Radar (NISAR) mission has provided important new insight into the Himalayan slope failure that preceded a deadly ice-and-rock avalanche in Nepal on August 26, 2026. Analysis of NISAR radar observations showed significant ground deformation in the weeks before the disaster, with several metres of displacement detected around the area where the avalanche eventually originated.
The observations are significant because they show how satellite-based radar can identify changes in difficult and remote mountain terrain before a major slope failure occurs. Researchers used Synthetic Aperture Radar (SAR) pixel-offset tracking to compare observations collected at different times. The analysis found that the movement was particularly concentrated on the upper section of the unstable Himalayan slope rather than being evenly distributed across the wider landscape.
The detected deformation suggests that the mountain slope was undergoing substantial movement before the ice-and-rock mass collapsed. Following the collapse, the falling material entered the valley and contributed to destructive downstream flooding and debris flows in areas near the Nepal-China border.
NISAR is particularly suited to monitoring such environments because its radar sensors can observe Earth’s surface during both day and night and can collect data through cloud cover. This capability is especially valuable in the Himalayas, where persistent clouds, rugged terrain and limited ground access can make conventional optical satellite observations difficult.
However, the latest findings should not be interpreted as proof that NISAR predicted the Nepal disaster. Detecting ground movement is different from forecasting when a slope will collapse. Mountain deformation can continue for extended periods without resulting in an immediate failure, meaning scientists need repeated satellite observations alongside geological, meteorological and ground-based data to assess the level of risk.
The NISAR mission could nevertheless become an important tool for Himalayan disaster-risk monitoring. ISRO says the satellite provides persistent, all-weather observations with a 12-day repeat cycle and is designed to study land and ice deformation, among other Earth-system processes. The mission also provides interferometric and pixel-offset data products that can be used to study changes in Earth’s surface.
The Nepal event therefore highlights a wider role for India’s space-based Earth observation capabilities. By repeatedly monitoring unstable slopes, glaciers and other high-risk areas, NISAR data could help researchers build a clearer understanding of how mountain systems change before landslides, avalanches and other natural hazards. While satellite observations alone cannot provide a definitive early warning, they can provide valuable evidence for scientists and disaster-management agencies working to identify potentially dangerous changes in remote terrain.
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