Dharali flash flood: 360 million cubic metres of glacial debris came tumbling down, experts estimate | India News

DEHRADUN: It wasn’t simply the rain. A preliminary geological evaluation carried out after Tuesday’s devastating flash flood in Dharali village, suggests a much more complicated and violent set off – a large collapse of glacial sedimentary deposits, presumably attributable to a retrogressive slope failure excessive up within the mountains.Initial estimates made by experts, primarily based on satellite tv for pc knowledge and terrain evaluation, level to an avalanche of practically 360 million cubic metres of debris. For perspective, a fast, back-of-the-envelope calculation reveals the determine is roughly equal to over 1.4 lakh Olympic-sized swimming swimming pools crammed with mud, rocks and glacial debris concurrently hitting the village at excessive velocity. With such an affect, it is not shocking that Dharali didn’t have an opportunity. The avalanche was mobilised by a sudden launch of unstable morainic and glacio-fluvial material-thundering down the Kheer Gad stream into Dharali. The surge reached the village inside seconds, flattening over 20 buildings and claiming lives of at the least 4 individuals (as per official figures).Imran Khan, geologist and head of the geology division at Bhutan’s Punatsangchhu-I hydel venture, who studied satellite tv for pc imagery of the world, stated “this wasn’t a typical cloudburst”. “The event likely involved a massive detachment of unconsolidated glacial deposits, perched roughly 7 km upstream at an elevation of 6,700m. Heavy rainfall may have acted as the trigger-but the disaster was waiting to happen.” The glacial deposit in query, spanning over 1.1 sqkm with an estimated vertical thickness of 300m, is situated in a dangling trough – an inherently unstable geological characteristic. The steep terrain, mixed with slender, pre-incised channels within the Kheer Gad stream, allowed the debris to speed up at terrifying speeds, leaving nearly no time for residents to flee. “The stream draining this area has a high longitudinal gradient, limited lateral confinement, and sharp incision paths-all of which contribute to rapid debris flow mobilisation,” Khan wrote. He added floor runoff and percolation, following days of intense rain, could have loosened the sediment, triggering the collapse.Rajiv Saran Ahluwalia, geologist at Doon University, advised TOI that at velocities of 6-7m per second, debris-laden flows are succesful of destroying any construction of their path. “And if the velocity doubles, the debris-carrying capacity increases by a factor of 64,” he stated. Experts imagine glacial soften, intensified by elevated temperatures within the days previous the catastrophe, could have compounded the instability. A senior glaciologist stated the exact trigger will solely be recognized as soon as real-time satellite tv for pc imagery – captured simply earlier than and after the occasion – is analysed or a floor staff conducts a survey upstream. “It appears the flash flood originated across three narrow valleys, with the most violent surge occurring in the Kheer Gad. Something extraordinary happened up there. It needs urgent investigation.”Geologists have for lengthy been calling for a ban on building alongside steep nala corridors and debris stream paths, significantly in pilgrimage-centric areas like Gangotri. “We can no longer afford to ignore hidden upstream hazards – especially in zones with growing human and pilgrimage footprints,” stated a geologist concerned within the evaluation.