The Teesta basin in the Sikkim Himalaya is home to several glacial lakes in the high-altitude, glacier-covered terrain. Among them, South Lhonak Lake stands out as one of the largest and fastest-growing.
Although these lakes are primarily situated in remote and uninhabited mountain valleys, the consequences of glacial lake outburst floods (GLOFs) can extend over tens of kilometres downstream, resulting in loss of human life and significant damage to property and infrastructure. A GLOF occurs when the weak, unstable natural moraine that holds a glacial lake fails can no longer hold the water in the glacial lake. Events like earthquakes, cloudbursts, and avalanches can trigger a GLOF by breaking the moraine.
A recent cloudburst above South Lhonak Lake caused it to breach its embankment, dumping the water into a channel that caused the water in the Chungthang dam reservoir to overflow as well as the reservoir itself to suffer damage. All this then triggered abrupt and devastating flash floods in different parts of the hilly state of Sikkim.
