The Himalayan landscape is shifting in ways that even the most seasoned experts find startling. On August 5, 2025, the town of Dharali in Uttarakhand was struck by a devastating flash flood that many initially blamed on a cloudburst, which is a sudden, extreme and localised downpour of rain.
However, a study by the Indian Space Research Organisation (Isro) has uncovered a different reason.
WHAT CAUSED THE DHARALI FLASH FLOOD?
Scientists from five different remote-sensing centres of Isro utilised high-resolution satellite imagery to reconstruct the disaster. Their findings, published in the journal Natural Hazards, reveal that the culprit was not a sudden rainstorm but a massive structural failure.
A 69-million-kilogram ice-patch, roughly the weight of 400 Blue Whales, collapsed on the Srikanta Glacier in Garhwal Himalaya, Uttarakhand. This frozen titan was located at a staggering altitude of 5,220 metres.
When it broke away, it triggered a chain reaction that sent a wall of water and debris hurtling towards the valley below.
WHY DID THE SRIKANTA GLACIER COLLAPSE?
The collapse happened in a nivation zone where the ice had become dangerously thin. A nivation zone is a high-elevation environment where persistent snow patches and buried ice trigger erosion.
While the region saw some rain between August 3 and 5, it was only light to moderate. This debunked the popular cloudburst theory.
Instead, the disaster was a cryo-hydrological event. This refers to a rapid, natural hazard triggered by the failure of cryospheric components such as ice patches, glaciers, and permafrost, which leads to water and debris release.
As the ice-patch fell 1,700 metres into the Kheer Gad channel, it converted its massive potential energy into kinetic force, churning up boulders and sediment. Eventually, this slurry reached Dharali with such speed that residents had almost no time to react.
IS GLOBAL WARMING MAKING HIMALAYAN GLACIERS DANGEROUS?
This event highlights a terrifying new trend in the Himalayas. Deglaciation, which is the disappearance of ice from a previously glaciated region, is creating unstable ice formations that do not need a heavy storm to fail.
The Isro study confirms that even a 30-centimetre-thick patch of ice can cause 100 per cent destruction if the terrain is steep enough.
This shift from traditional glacial melts to sudden ice-patch collapses means our early-warning systems must now monitor even the smallest frozen patches above mountain villages.
