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5 Octber 2023
Introduction:
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.