Sikkim’s South Lhonak Lake Triggers Deadly Floods

October 5, 2023

In a tragic incident, the South Lhonak Lake in Sikkim experienced a breach, leading to severe flooding in downstream areas. This caused casualties and displacements in the state.

Glacial Lakes and Their Nature

Glacial lakes are large bodies of water formed in front of, on top of, or beneath melting glaciers.
They can become increasingly dangerous as they expand, often dammed by unstable ice or sediment composed of loose rock and debris.

Glacial Lake Outburst Floods (GLOF)

Glacial lake outburst floods (GLOF) occur when the boundaries of these lakes break, causing a sudden and massive rush of water down mountainsides.
GLOFs can be triggered by various factors, including earthquakes, heavy rainfall, and ice avalanches.

Vulnerability of South Lhonak Lake

Rising global temperatures have led to rapid glacier melting in the Sikkim Himalayas, resulting in the formation and expansion of glacier lakes.
Sikkim Himalayas currently host more than 300 glacial lakes, with 10 identified as vulnerable to outburst floods.
South Lhonak Lake’s size has significantly increased over the past five decades, rendering it susceptible to GLOF events.
Earthquakes, such as a magnitude 4.9 quake in 1991 and a magnitude 6.9 event in 2011, have raised concerns about the potential triggering of GLOFs in the region.

Government Action to Mitigate Risk

Recognizing the risk posed by South Lhonak Lake, the Sikkim government took proactive measures in 2016.
A team from the Sikkim State Disaster Management Authority, along with experts, implemented a syphoning technique supervised by innovator Sonam Wangchuk.
This involved the installation of HDPE pipes to gradually reduce the lake’s water levels, mitigating the threat of a catastrophic outburst.

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