WARNING FROM THE HIMALAYAS

A wall of water hurtling down mountains towards vulnerable valleys nestled within— this worst nightmare of Himalayan states came true for Sikkim on October 4 when the waters of the Lhonak lake in north Sikkim, situated at an altitude of 5,245 metres, burst forth and flooded regions in the Teesta river basin, killing many and washing away roads and bridges downstream

-  Arkamoy Datta Majumdar

Moreover, the mass of water swept away the 1,200 MW Teesta III hydel power dam at Chungthang 65 km downstream and severely damaged the 510 MW Teesta V and the under-construction Teesta VI hydel projects further down the river. The cause was a Glacial Lake Outburst Flood (GLOF) possibly caused by heavy rains that triggered a landslide. A GLOF is a sudden release of water from a lake fed by glacier melt after a retreating glacier—the Lho nak glacier in this case—leads to its fast expansion. After the catastrophe, it was revealed that around half of the Lhonak lake has been drained out. To make matters worse, there was a paucity of an effective early warning system—a de rigueur procedure—and, during the mishap itself, a breakdown of coordination on the ground at the dams. However, the Sikkim disaster wasn’t a complete surprise, for the rapidly expanding Lhonak lake had long been red-flagged by experts from central agencies as being particularly susceptible to a GLOF event. Also, locals’ concerns over constructing power projects on the Teesta, in such an ecologically fragile region, had been set aside by authorities a decade back.

In 2013, the National Remote Sensing Centre published a study that showed that the Lhonak lake has a high outburst value of 42 per cent and that, according to satellite images, between 1962 and 2008, the South Lhonak glacier retreated 1,941 metres, making the lake one of the fastest growing in the Sikkim Himalayas.