2 months ago
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A caller survey by scientists from the Indian Space Research Organisation (ISRO), published successful NPJ Natural Hazards, examines the August 5, 2025 flash flood that destroyed Dharali village successful Uttarakhand and killed six people. It sheds airy connected however warming temperatures impact glaciers, particularly exposed crystal patches connected retreating glaciers, and highlights the request to show glaciers utilizing outer images to supply aboriginal warnings of imaginable disasters.
The study, titled ‘Ice-patch illness and early-warning implications from a Himalayan flash flood: emerging cryo-hydrological hazards nether deglaciation’, concludes that the illness of an crystal spot connected the glacier supra Dharali is linked to deglaciation successful the Himalaya.
The authors accidental the findings could assistance amended knowing of clime hazard and catastrophe preparedness. The survey shows that the flash flood was triggered by the illness of an crystal spot successful the nivation country of the Srikanta glacier.
Nivation is defined arsenic the erosion of the crushed beneath and astir a snowfall bank, chiefly arsenic a effect of alternate freezing and thawing. This tin signifier a nivation hollow, which gradually becomes deeper erstwhile snowfall repeatedly accumulates successful the aforesaid place.
History of utmost events
The survey country lies successful the precocious Bhagirathi stream basin successful Uttarkashi territory of Uttarakhand. It covers the ridge-to-valley strategy from the Srikanta glacier to Dharali village, located astatine a tallness of 2,650-2,700 m on the Bhagirathi river. The colony lies downstream of the glacier-fed Khir Gad stream, which originates from the Srikanta glacier, flows done Dharali, and past joins the Bhagirathi river. The Khir Gad divides Dharali into right- and left-hand slope settlements, expanding its hazard of flash floods.
The portion has a documented past of utmost events, including the ample landslides that brought down monolithic boulders during the June 2013 Himalayan floods. The researchers utilized outer observations, high-resolution topographic analysis, and ocular records to reconstruct the series of events linking unstable glacier crystal to the abrupt flood.
The findings grow the scope of recognised glacier-related hazards successful the Himalaya and place exposed crystal patches arsenic an under-recognised hazard from glacier melt.
The Dharali lawsuit besides shows however instability successful the cryosphere tin make hazards downstream successful high-altitude regions.
Exposed crystal patches
The survey calls for person monitoring of glaciers and argues that the absorption should widen beyond glacial water outburst floods (or GLOFs) to see smaller, often overlooked instabilities successful the cryosphere. The vulnerability of crystal patches successful the Srikanta glacier earlier the flood represents a transitional authorities successful the snow-ice regime.
“Pre-event imagery during the ablation play revealed exposed crystal patches connected steep north- to northeast-facing slopes, indicating thinning seasonal snowfall and firn screen accordant with ongoing deglaciation,” the authors wrote successful the paper.
Such vulnerability indicates thinning seasonal snowfall and firn, which is crystal that lies betwixt snowfall and afloat formed glacial ice.It usually occurs erstwhile warmer conditions trim the insulating snowfall furniture that stabilises the crystal beneath.
Ice patches covered by firn and seasonal snowfall are comparatively resistant to short-term somesthesia changes whereas exposed crystal is much apt to displacement oregon loosen. Because exposed crystal responds much rapidly to somesthesia changes oregon dense rainfall, it tin melt, fragment oregon illness much easily, releasing ice, meltwater, and debris that tin trigger flash floods.
Therefore, the survey finds that the beingness of exposed crystal patches connected the Srikanta Glacier instantly earlier the floods of August 5 was a awesome of ongoing deglaciation and a nonstop indicator successful the scenery that accrued the likelihood of specified floods.
Satellite observations
Srikanta Glacier is simply a small- to medium-sized vale glacier with a tallness of 6,133 m, astir 9.8 km upstream of Dharali. The glacier has steep accumulation and ablation zones, seasonal snowfall cover, and extended nivation areas. Mountaineering and expedition reports picture unstable crystal surfaces, steep slopes, avalanche-prone terrain, and persistent nivation zones beneath the ridge beneath the Srikanta peak, the insubstantial said.
A cardinal accusation of the survey is that it shows the worth of pre-event outer observations for aboriginal warning. Satellite images showed exposed crystal patches persisting successful the nivation portion during the ablation period, erstwhile the glacier loses crystal and snow. This indicated that the seasonal snowfall and firn screen had thinned.
Studies from different acold regions, including the Canadian Arctic and Greenland, besides amusement that the illness of crystal patches tin trigger hazards arsenic glaciers suffer much crystal and snowfall owed to determination warming.
Identifying nivation hollows
Although seldom reported from the Himalaya, events specified arsenic the February 2021 Chamoli rock-ice avalanche show the increasing prominence of cryospheric hazards successful deglaciating terrain, the survey said. In steep nivation hollows, specified instability tin abruptly merchandise ice, meltwater, and debris, triggering downslope wide question and related cryo-hydrological hazards.
The Dharali flash flood illustrates however cryospheric instability tin trigger geomorphic changes and make hazards downstream successful high-altitude Himalayan regions. The survey finds that the accelerated disintegration of an exposed crystal spot successful the nivation portion of the Srikanta glacier was the main origin of the event.
The reconstructed sequence, from the vulnerability of the crystal spot during the ablation play to its disappearance and the resulting downstream impacts, shows however earth-observation information tin assistance place and reconstruct specified utmost events successful distant upland terrain.
“A broader accusation of this investigation is the recognition of nivation hollows arsenic geomorphologically delicate zones for cryospheric instability,” the authors concluded.
“Persistent snowfall and crystal retention connected north- to northeast-facing slopes beneath the Srikanta ridge created conditions conducive to ice-patch vulnerability and consequent nonaccomplishment during the ablation season. Similar settings are wide crossed the Himalaya, suggesting that systematic recognition and monitoring of specified zones should signifier portion of determination hazard assess- ment and disaster-risk simplification strategies successful the discourse of ongoing deglaciation
Meena Menon is an autarkic journalist, researcher and author. She has a PhD from the University of Leeds.
