Uttarakhand: Underground glacial lake led to flash floods, says IISc analysis

The Divecha Centre for Climate Change at Indian Institute of Science, Bengaluru, has found clues to the origin of the flash floods in Uttarakhand’s Rishiganga valley on Sunday. The team has concluded that release of water from an underground glacial lake led to flash floods and inundation in the valley.

Using a tool to map depression in the bedrock below glacier ice in northern Nanda Devi, the team said images suggest a depression of 25ha upstream of the glacier terminus.

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.

“This is a new tool developed in IISc by our team which can be very useful to study such disasters. The tool 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,” said Professor Anil Kulkarni, distinguished scientist, Divecha Center for Climate Change.

Responding to some US-based scientists who had suggested that a landslide had triggered the flash floods based on satellite data, Kulkarni said “It appears to me that they looked at the adjacent valley. 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.”