Troubled Waters

Multiple massive glacial lakes in the Sikkim Himalayas have been identified as 'high risk' to sudden breaching

- Snigdhendu Bhattacharya IS A JOURNALIST, AUTHOR AND RESEARCHER

SHAKO Chho—a glacial lake the size of approximately 70 standard football fields—is located at an altitude of 4,982 metres in the eastern Himalayas. If its embankments breach, the millions of cubic litres of water that it holds would gush out—taking glacial debris along—and can hit the nearest human habitation, Thangu valley, in just seven minutes. The flood's fury can flatten everything in its way.

Thangu valley stands about 10 km downstream of Shako Chho at an altitude of 3,960 metres in north Sikkim. It has a population of a few hundred people and serves as a popular acclimatisation place for trekkers to higher altitude destinations close to the Indo-China border, such as the Gurudongmar lake and Cho Lhamu—the source of the River Teesta.

The people of Thangu valley, known as the Lachenpa, are ethnic Bhutias. They practise a semi-nomadic life, living in Thangu, where all their farmlands are, during the summer and monsoon months. But in winter, Thangu is covered in thick layers of snow. The Lachenpas then descend to their second home, Lachen, itself a popular tourist destination at an altitude of 2,750 metres.

Over the past few years, Thangu has also been drawing many scientists working with different government institutions. Shako Chho has been identified as one of the lakes in the Indian Himalayas that pose the highest risk from glacial lake outburst floods (GLOFs) for the people living downstream.

According to the March 2023 report that estimated a seven minute duration for the flood’s fury to reach Thangu from Shako Chho, due to its location next to the river and a short warning time, Thangu is in “a very critical high-risk situation, and would be heavily affected, even under a moderate GLOF scenario.” Besides, options for evacuation routes and safe zones are “very limited.”