Sikkim Identifies 40 High-Hazard Glacial Lakes; 16 At Immediate Risk Of Outburst Floods

The eastern Himalayan state of Sikkim has identified 40 high-hazard glacial lakes, with 16 of them classified as being at the highest risk of catastrophic outbursts that could threaten downstream settlements. The findings were disclosed at a media sensitisation workshop on Glacial Lake Outburst Flood (GLOF) risk mitigation held Thursday at the Conference Hall of the Department of Science and Technology in Gangtok. The data carries particular significance given its timing, coming against the backdrop of the recent flash flood in Nepal, which was triggered by a glacial collapse near the Nepal-Tibet border on August 26 and left a trail of destruction, with hundreds of people dead and scores still missing.

Although that disaster was not directly linked to a Glacial Lake Outburst Flood, it has drawn renewed attention to a broader transformation occurring across the Himalayas, as retreating glaciers give way to new lakes while existing ones continue to expand in size. According to Sandeep Tambe, Principal Secretary of the Departments of Science and Technology and Education, of the 40 high-hazard glacial lakes identified in Sikkim, 16 fall under Category A, representing the highest risk classification, while two are placed in Category B, indicating high risk. A further nine lakes fall under Category C, denoting moderate to low risk, and 13 lakes remain unclassified pending further assessment.

Tambe said the state is relying on remote sensing techniques and satellite imagery to closely monitor changes in the size and spread of these glacial lakes over time. Glacial lakes form through the melting of glaciers, with meltwater accumulating in depressions on or near a glacier's surface. GLOFs occur when these lakes suddenly burst open, often triggered by factors such as excessive water accumulation or external shocks like earthquakes, releasing massive volumes of water and debris downstream with little warning. Sikkim has firsthand experience with the devastating consequences of such events: a major glacial lake outburst in October 2023 resulted in at least 60 fatalities and caused extensive damage across the Mangan, Gangtok, Pakyong, and Namchi districts, while also destroying the Chungthang dam, a critical component of a major hydropower project in the state.

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D.G. Shrestha, Principal Director-cum-Secretary of the Department of Science and Technology, recalled the extensive damage suffered during the 2023 disaster and said the state government is now focused on protecting Sikkim against future glacial flood events by developing early-warning systems and building more resilient infrastructure, while also safeguarding critical assets such as roads, dams, bridges, and settlements. "Sikkim must position itself as a national leader in GLOF risk mitigation," Shrestha said, underscoring the state's ambition to serve as a model for other Himalayan regions confronting similar risks.

Officials said detailed field investigations have already begun at vulnerable sites, encompassing a range of technical assessments including remote sensing, water discharge and level monitoring, Electrical Resistivity Tomography, geophysical surveys, and DGPS-based evaluations. The Department of Science and Technology is also developing a broader mitigation proposal in collaboration with the Brahmaputra Board, aimed at reducing GLOF-related threats while preserving the cultural and religious significance that many of these high-altitude lakes hold for local communities.

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