The flash floods in Uttarakhand’s Rishiganga valley on Sunday had left everyone wondering about the cause behind. The fragile ecology of the mountainous state has been scoured by many environmental disasters in the last decade.
Initial reports suggest that flash flood was caused due to breaking of Nanda Devi glacier. The observation was widely published by numerous news media and also supported by reconnaissance survey carried out by the Indian Air Force.
“We went deeper to see what happened under the surface,” Professor Anil Kulkarni, distinguished scientist, Divecha Centre for Climate Change at Indian Institute of Science, Bengaluru, was quoted as saying by Hindustan Times.
Kulkarni-led research team from the institute has concluded that instead, the release of water from an underground glacial lake led to flash floods and inundation in the valley.
The researchers used a new tool developed in IISc by them which is based on Laminar flow equation and surface slope; known as Himalayan Glacier Thickness Mapper (HIGHTHIM).
The tool was used successfully to map depressions below South Lhonak lake in Sikkim and further estimate the future expansion of the lake. It can be very useful to study disasters.
The team used the tool to map depression in the bedrock below glacier ice in northern Nanda Devi, and the resulting images suggested a depression of 25ha upstream of the glacier terminus. The release of water from this underground glacial lake led to flash floods and inundation in the valley.
This underground lake has a capacity to store 4.5 million cubic metres of water. The lower part of the ablation zone (zone of the glacier which has melted or calved and formed a lake) is also receiving a significant amount of water from a tributary glacier located at the northern side of the Nanda Devi glacier.
“If this depression filled with water develops appropriate hydrostatic pressure, it can accelerate the lower part of the ablation zone, possibly releasing water from the underground lake. It could be the potential reason for the flash flood,” a note prepared by the IISC team said.
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