The toll in the glacial lake outburst flood (GLOF), originating from the high altitude South Lhonak reservoir in North Sikkim, which raged into the Teesta River basin, had surged to 22 on Thursday. Close to 102 people, including 22 Army staffers are missing. The flood has damaged the Chungthang dam, a critical component of the largest hydropower project in the state – the Teesta-3, situated along the Teesta River that criss-crosses Sikkim, West Bengal and Bangladesh.
The damage to Sikkim’s infrastructure is manifold as the flood destroyed 11 bridges. The National Highway-10 also sustained significant damage in many parts. This is not another episode of nature unleashing its agitation arbitrarily, as the warning signs were there all along. Over the past two decades, researchers and government agencies have warned about potential GLOFs in Sikkim that could lead to extensive damage to life and property.
Such floods take place when lakes formed by melting glaciers suddenly burst open. This could be triggered by various causes including excessive water accumulation in the lake or even earthquakes. Upon bursting, the lake releases a massive quantity of water at once, causing flash floods downstream. The South Asia Network of Dams, Rivers, and People, have referred to the South Lhonak Lake as a glacial-moraine-dammed lake, and it is one of the fastest-expanding lakes in the Sikkim-Himalaya region. It has further been classified as one of the 14 potentially dangerous lakes susceptible to GLOFs.
Located at an altitude of 17,100 ft above sea level and formed due to the melting of the Lhonak glacier, the lake’s size has been rapidly increasing. This is due to the melting of the lake’s associated South Lhonak glacier as well as additional meltwater from the adjacent North Lhonak and main Lhonak glaciers. Currently, the lake has more than tripled in size – from 0.42 sq km to 1.35 sq km in less than 30 years. Satellite images from the National Remote Sensing Centre showed that the area of South Lhonak Lake had drastically reduced from 167.4 hectares on Sept 28, to 60.3 hectares on Oct 4. The reduction confirms the GLOF event that caused massive damage in the Teesta River basin.
Researchers say that there are 14 other glacial lakes in Sikkim that are just as large and vulnerable. The role of global warming in accelerating the speed of melting of glaciers is also being probed. Close to 70% of glacial lakes in the Hindu Kush-Himalayas, which has around 7,500 glacial lakes, are vulnerable to events such as landslides and avalanches. On Friday, a fresh alert was issued along the Teesta river, and authorities have warned that yet another glacial lake, the Shako Cho Lake, near Lachen is on the verge of bursting in the northern part of the state. The GLOF was expected to make a landfall near Thangu beyond Lachen in Mangan district.
These developments are a reminder of the disdain with which the government and private enterprises treat ecological sustainability, vis-a-vis infrastructure development in mountainous regions. We have seen the results of unplanned, development in hill-side towns in Uttarakhand as well as Himachal Pradesh. Climate resilience and vulnerability mapping should assume centrestage when charting growth plans in high altitude regions of the country.