ISRO Overturns Cloudburst Theory: Exposed Ice Patch Above 5,200 Metres Destroyed Dharali

A detailed scientific investigation by the Indian Space Research Organisation has found that the deadly 2025 flood in Dharali village of Uttarkashi district was not triggered by a cloudburst, as initially suspected. Instead, scientists concluded that the disaster was caused by the sudden collapse of an exposed ice sheet high above the village near the Srikanta Glacier, highlighting a lesser-known hazard linked to climate change in the Himalayas.

The flood struck on August 5, 2025, when a powerful surge of water, mud, ice, and boulders rushed down the narrow valley and devastated Dharali, a village located along the Bhagirathi River. The torrent destroyed homes, collapsed hotels, and buried large parts of the marketplace situated along the glacier-fed Khir Gad stream. Residents recorded dramatic footage of a sudden, violent wave of debris that lasted briefly before transitioning into slower muddy flows.

Scientists initially examined whether the event was caused by a cloudburst or a glacial lake outburst flood (GLOF), both common explanations for sudden Himalayan floods. However, rainfall data from the India Meteorological Department showed only light to moderate rain in the region before the disaster, ruling out a cloudburst. Satellite imagery also confirmed that no glacial lakes were present upstream that could have burst, eliminating the possibility of a GLOF.

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Using high-resolution satellite images, digital elevation models, and videos recorded by villagers, the ISRO team traced the origin of the flood to a steep slope more than 5,200 metres above sea level below the Srikanta Glacier. The location contained a “nivation zone,” a shaded hollow where snow and ice accumulate over years. In July 2025, satellites detected unusually exposed ice patches in this area, which had previously been covered by protective snow layers.

Rising temperatures and glacier thinning had stripped away this protective cover, leaving the ice vulnerable. A large ice patch covering roughly a quarter of a square kilometre eventually collapsed, releasing meltwater, ice blocks, and debris. Because the ice patch sat on a steep slope of around 30 degrees, the material accelerated rapidly downhill through a narrow valley corridor dropping more than 2,500 metres over about nine kilometres, gathering rocks, soil, and old landslide debris along the way.

By the time the mass reached Dharali, it had transformed into a powerful debris flood capable of causing widespread destruction within seconds. The study warns that such ice patch collapses—rarely documented in the Himalayas before—may become more common as glaciers retreat and snowlines move higher due to warming temperatures. Scientists say satellite monitoring, especially using radar systems that can see through monsoon cloud cover, could help detect unstable ice patches earlier and improve disaster warning systems in vulnerable Himalayan regions.

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