Twenty-one other glacial lakes in the Teesta river basin show potential threat
Scientists had warned in 2021 that the South Lhonak lake in Sikkim would burst. The disaster finally took place on the intervening night of October 3-4, 2023.
The detailed study, Future Glacial Lake Outburst Flood (GLOF) hazard of the South Lhonak Lake, Sikkim Himalaya, highlighted that South Lhonak Lake had witnessed a significant increase in lake growth in the past decades due to glacial retreat, thereby increasing its chances of glacial lake outburst floods (GLOF).
The lake, at a height of 5,200 meters above sea level, became the largest and fastest-growing glacial lake in the state, with a glacial retreat of almost two kilometres in 46 years between 1962 and 2008. Scientists recorded another 400-metre retreat of the glacier between 2008 and 2019, increasing the hazard potential.
The length of the glacier has reduced from 6.4 km to 5.1 km in 29 years. Overall, the glacier shrunk by about 0.96 sq km. The Central Water Commission of the central government had also initiated an advisory to evaluate the condition of the lake system.
According to the census of 2011, the Chungthang village downstream houses over 10,000 residents, who are now cut off from the world.
The study also noted that:
The width of the terminal moraine that dams the South Lhonak Lake is not uniform and is thinning towards the ends. Hummocky surface of the dam indicates that it likely contains buried ice and be subject to future degradation.
It further stated that the moraine’s stability would alter over time and compromise the structural integrity due to melting of buried ice and impact of waves that could lead to overtopping flows. Extreme meteorological conditions such as cloudbursts would result in quick overfilling of the lake, initiating progressive erosion.
Scientists also point out that climate change is causing an impact on Himalayan glaciers and glacial lakes. In a chapter — Global Climate Change and Melting of Himalayan Glaciers — published in the book, Melting Glaciers and Rising sea levels: Impacts and implications, researchers claim the glaciers to be retreating at 10 to 60 metres per year.
Another study — Remote sensing-based inventory of glacial lakes in Sikkim Himalaya: semi-automated approach using satellite data — published in 2012 states that the number of glacial lakes in the Sikkim Himalayas are increasing and prone to GLOFs.
A study done by the International Centre for Integrated Mountain Development (ICIMOD) in 2003 using satellite data observed that of the 266 glacial lakes located in the Sikkim Himalayas along the Teesta basin within an area of 20.20 sq km, 14 were potentially hazardous lakes.
The number of lakes increased to 320 in 2010. Of the 14 dangerous lakes, three showed evidence of past GLOFs. Another two lakes indicated reduction in area in 2010 which may be attributed to discharge or an outburst event.
Of the 14 dangerous lakes, 12 were identified to have shown an increase in area between 2003 and 2010. The reason for the change is climate change which caused glacial retreat.
A study, Glacial Lake Evolution (1962–2018) and Outburst Susceptibility of Gurudongmar Lake Complex in the Tista Basin, Sikkim Himalaya (India), published in Multidisciplinary Digital Publishing Institute highlights the potential risk of the Gurudongmar lake complex (GLC) causing an outburst.
Between 1962 and 2018, the overall lake area has increased by 74 sq km due to climate-driven factors. The study noted, “This outburst susceptibility assessment revealed that the entire complex consisting of three lakes has high risks of potential hazard in terms of outbursts or overflow.”
The researchers pointed out that by 2028, if global temperatures follow the same graph of increase in the Gurudongmar semi-arid region, the crevasses that have formed in the steep terrain near the icefall area of the GLC which comprises of three glacial lakes — GL-1, GL-2, GL-3 — will shrink.
The area will further shrink with accelerated melting and calving process, resulting in the creation of outward cryostatic pressure exerted by ice and inward hydrostatic pressure, which is exerted by water near the terminus of lake GL- 3.
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
Photo: from the Facebook wall of Prem Singh Tamang-Golay, Sikkim CM.png)
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.