A Restless Himalayan Slope Is Building a Deadly Flood Time Bomb

High in the Kumaun Himalaya of Uttarakhand, India, a mountainside above the tiny village of Kuwari has been quietly assembling the ingredients of a catastrophe. Since 2013, the Kuwari landslide has lurched back to life again and again, each reactivation dumping fresh debris into the Shambhu River, a tributary of the Pindar River in Bageshwar district. That debris has repeatedly dammed the river, impounding a growing lake that now holds an estimated 3.7 million cubic meters of water. A new study by researchers at India’s National Remote Sensing Centre of ISRO, published in Discover Geoscience, has reconstructed twelve years of the landslide’s behavior using satellite imagery, radar interferometry and hydrodynamic modeling, and the picture it paints is sobering: the natural dam holding back the lake is unstable, and a sudden breach could send a violent flood surging through villages downstream.

The team, led by Ankita Ghoke, Priyom Roy and colleagues, combined three complementary lines of evidence to track the slope’s evolution. Eighteen cloud-free optical images from Indian Resourcesat-2 and 2A satellites, the European Sentinel-2 mission and the high-resolution Cartosat-3 sensor allowed them to map morphological changes between 2013 and 2025. They then applied multi-temporal interferometric synthetic aperture radar, or MT-InSAR, using the Small Baseline Subset technique on Sentinel-1 radar data to measure millimeter-scale ground deformation over four distinct time windows. Finally, field campaigns after the 2024 reactivation documented the structural and geological weaknesses that make the slope so prone to failure. Together, these datasets reveal a landslide that is not a single event but a slow-motion, retrogressive collapse that keeps climbing uphill and swallowing new ground.

The optical record tells a striking story of escalation. In March 2013, the unstable zone was a modest, elongated feature roughly 500 to 600 meters long. A major reactivation in June 2013, coinciding with the disastrous Kedarnath cloudburst that devastated much of Uttarakhand, stretched the slide to about 965 meters and carved the first prominent head scarp while blocking the Shambhu River. Between 2014 and 2016 the failure continued to retreat upslope, damming and re-damming the river. Around October 2018, an entirely new landslide initiated to the southwest, and by late 2019 its scar had merged with the main slide mass, enlarging the failure zone still further. By 2024, four separate head scarps were visible on the slope, evidence of multi-scarp retrogression still underway. The landslide now covers approximately 0.95 square kilometers, and imagery shows that several settlements in its path were destroyed as it grew.

The radar measurements add a crucial dimension: they show the slope moving before it visibly fails. In the first analysis phase, from October 2014 to October 2016, monitoring points on the flanking slopes recorded average line-of-sight velocities of roughly 40 millimeters per year, with deformation accelerating during the 2015 and 2016 monsoons before complete failure and scarp formation. In the second phase, a point tracking the nascent secondary landslide crept at 13.6 millimeters per year before a rapid acceleration culminating in the October 2018 collapse. Later phases recorded velocities between about 5 and 12 millimeters per year, each acceleration episode closely following periods of intense rainfall. The pattern is classic transient landslide behavior: stability, then primary creep, then accelerating motion, then failure, with monsoon precipitation acting as the trigger on a slope already predisposed to collapse by its geology.

That geology is unfavourable in almost every respect. The slope lies near the Main Central Thrust in the seismically active Lesser Himalaya, underlain by highly sheared talc schist, carbonaceous phyllite, quartzite and slate of the Lameri Formation, all draped in thick, loose colluvium. Fieldwork revealed foliation planes dipping at 45 to 50 degrees, parallel to the slope face, creating ready-made planar failure surfaces. The team also mapped transverse cracks, active groundwater seepage channels exuding along those cracks, and linear discontinuities that appear to be faults or joints. Particularly worrying is the village of Kuwari itself, which sits on a previously stabilized portion of the landslide body that field evidence now shows is bulging and deforming anew. A road constructed across the secondary landslide zone in early 2022 has further destabilized that section, a reminder that human activity can amplify an already fragile situation.

Meanwhile, the lake behind the debris dam keeps growing. The first impoundment formed in June 2013 and drained in 2015; a second formed in November 2016, partially drained in October 2017 and re-formed in 2018. From November 2021 onward the water body expanded relentlessly: roughly 885 meters long by April 2022, about 900 meters by October 2022, 1,050 meters by October 2023, and approximately 1,130 meters long and 100 meters wide by October 2024, the largest extent on record. Each enlargement reflects fresh debris choking the valley and raises the volume of water poised above downstream communities. History offers little comfort: previous research indicates that 80 to 90 percent of landslide-dammed lakes fail within their first year, and the Kuwari dam has already been partially breached by the river cutting a narrow channel through the debris.

To assess how stable that dam actually is, the researchers applied two geomorphic indices. The Morphological Obstruction Index, calculated at 3.82, places the dam in the uncertain evolution domain, while the Hydro-morphological Dam Stability Index, computed from the dam volume, upstream catchment area of about 2.46 square kilometers and channel gradient, falls squarely within the instability domain. The dam itself is a type III barrier in the classification of Costa and Schuster, meaning debris has moved both upstream and downstream of the valley and completely obstructs it. With an estimated height of around 40 meters and a surface area near the crest of roughly 10,000 square meters, the structure is an unconsolidated pile of landslide debris, not engineered material, and it is already being eroded by the river flowing through it.

The most dramatic part of the study is the flood simulation. Using HEC-RAS version 6.7, the team modeled a complete overtopping breach of the dam, drawing breach geometry from an empirical relationship derived from historical dam failures. Assuming the full 3.7 million cubic meter reservoir and a 17-meter breach height, the model predicts an average breach width of 48.3 meters forming in just 0.64 hours, less than forty minutes. The resulting flood would race down the narrow valley at a peak velocity of 15 meters per second near the breach, with overbank flooding extending about six kilometers downstream to Choting village, where water could rise up to 10 meters above normal levels and inundate agricultural terraces. Beyond Choting, the flow would remain channelized but still dangerous, reaching the villages of Melkhet, Deosari and Dewal at average velocities of 6 to 8 meters per second, fast enough to threaten anything along the riverbanks.

The authors are careful to note that the simulation is a predictive, end-member scenario that cannot yet be validated, and that its results carry uncertainties in breach width, formation time, erosion rates and dam material properties. But the broader message is hard to escape. The Kuwari landslide is an active, compound hazard in one of the world’s most landslide-prone countries, which a global analysis by Froude and Petley ranked highest in landslide fatalities. The study’s authors call for continuous monitoring, an early warning system for downstream communities, slope stabilization measures, and strict controls on construction across already scarped slopes. As climate change intensifies monsoon extremes across the Himalaya and infrastructure development pushes further into fragile terrain, the integrated approach demonstrated here, pairing satellite radar with optical imagery, field geology and hydrodynamic modeling, may become an essential template for spotting the next Kuwari before its lake bursts.

Subject of Research: Reactivation dynamics of the Kuwari landslide in Uttarakhand, India, and assessment of landslide lake outburst flood hazard using remote sensing and hydrodynamic modelling.

Article Title: Reactivation dynamics of the Kuwari landslide (Uttarakhand, India) and assessment of LLOF hazard using optical imagery, MT-InSAR and hydrodynamic modelling

Article References: Ghoke, A., Gaur, A., Roy, P., Jalan, P., Martha, T. R., & Das, I. C. (2026). Reactivation dynamics of the Kuwari landslide (Uttarakhand, India) and assessment of LLOF hazard using optical imagery, MT-InSAR and hydrodynamic modelling. Discover Geoscience, 4(1), Article 345. https://doi.org/10.1007/s44288-026-00717-w

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00717-w

Keywords: Kuwari landslide, Uttarakhand, Himalaya, MT-InSAR, landslide-dammed lake, LLOF, HEC-RAS, Sentinel-1, dam breach, natural hazards, remote sensing, monsoon rainfall