Technique to predict glacial lake bursts

Scientists at the Indian Institute of Science (IISc) in Bengaluru have developed a new technique to predict the growth of glacial lakes and identify those likely to burst. Applying the technique to study the South Lhonak lake – one of the largest in the Sikkim Himalaya and recognised already as potentially hazardous – the researchers found that it is expanding "dangerously" and needs to be watched.

The institute’s Divecha Centre for Climate Change (DCCC) studied the South Lhonak Lake, situated at an altitude of about 7000 meters, with collaborators from the Sikkim State Council of Science and Technology. "The rate of growth of the lake indicates possible development of a hazard situation," Remya Namboodiri, a DCCC scientist and lead author of the report told Nature India .

The lake is growing larger every year and has become the most dangerous glacial lake in the region, their report says. The researchers estimated that the 51.4 metre-deep lake could swell up in volume from about 60 million cubic metres in 2015 to about 90 million cubic meters in future. "Once it bursts, this enormous amount of water can cause chaos downstream," they warn.

Glacial lakes are formed when glaciers, retreating due to climate change, leave behind large deposits of ice in hollows. When it melts, this ice creates the lakes.

Dammed by rocks, boulders and loose soil – called moraine – these lakes are like ticking time bombs. Sudden discharge of large volumes of water from them – or Glacial Lake Outburst Floods (GLOFs) – are known to cause havoc downstream. The Himalayan region has been witness to many such flash floods in the past – the 1926 Jammu and Kashmir deluge, the 1981 Kinnaur valley floods in Himachal Pradesh and the 2013 Kedarnath outburst in Uttarakhand.

Satellites have been keeping an eye on these water bombs lurking in glaciers. However, remote sensing cannot estimate the depth (and hence volume of water) of glacial lakes, or when disaster is likely to strike. So the DCCC researchers adopted a technique using parameters such as glacier surface velocity, slope and laminar flow of ice to estimate the volume and expansion of the lakes and identify the unsafe ones. The technique has been automated using 'Python' computer programming language.

They have also mapped nine other glacial lakes in the region and three sites where new lakes may form in future. According to the report, the technique can be used for monitoring glaciers in other regions of the Himalaya to warn people about imminent flash floods. With the Himalayan glaciers retreating fast, it is necessary to make a systematic inventory of glacial lakes and establish their hazard potential, it says.

"An early warning system coupled with GLOF simulation models capable of predicting the time of arrival of the flash floods and showing the flooded areas downstream will enable the local authorities to take precautionary measures," Namboodiri said.

M. Rajeevan, Secretary of India's Ministry of Earth Sciences said "we do not have any operational warning system for glacial lake outburst flooding at present." He, however, did not say if his ministry is planning one in the light of potential threat in the Sikkim Himalaya.

References

1. Remya, S. N. et al. Volume estimation of existing and potential glacier lakes, Sikkim Himalaya, India. Curr. Sci. 116 (2019) Article