In Sikkim, authorities have identified 40 glacial lakes categorized as high-risk, with 16 of these classified under the critical Category A designation, amid rising fears regarding glacial lake outburst floods (GLOFs) in the Himalayas. The state is actively developing a mitigation strategy to monitor these lakes and implement potential flood-prevention measures, highlighting Shako Chho Lake as the most at-risk site.
This assessment has been prompted by the devastating flash flood in Nepal on August 26, which resulted in over 1,200 fatalities. Although this particular disaster stemmed from an ice and rock collapse rather than a GLOF, it has heightened concerns about the increasing susceptibility of Himalayan communities to climate-related threats.
During a media workshop focused on GLOF risk management, Sikkim’s Principal Secretary, Sandeep Tambe, mentioned that satellite imagery and remote sensing technologies are being utilized to monitor alterations in glacial lakes.
Among the identified high-risk lakes, 16 fall under Category A, indicating the highest level of threat. Additionally, two lakes are categorized as Category B, representing a high risk, while nine are classified in Category C, indicating a moderate to low risk. The classification status of the remaining 13 lakes is still pending, as noted by Tambe.
Glacial lakes are formed by the melting of glaciers, which leads to water accumulation in surrounding depressions. A sudden release of water from these lakes, triggered by excessive rainfall, landslides, or seismic activity, can unleash significant torrents of water, mud, and debris downstream.
Sikkim has already witnessed the catastrophic consequences of such an event; a GLOF in October 2023 resulted in at least 60 deaths and caused extensive damage to infrastructure in Mangan, Gangtok, Pakyong, and Namchi, in addition to destroying the Chungthang dam, as reported by PTI.
Shako Chho Lake has been pinpointed as the most susceptible to a GLOF, and a comprehensive project proposal for mitigation efforts at this lake has been submitted to the National Disaster Management Authority. Additionally, a preliminary report has been forwarded to the Jal Shakti Ministry.
For the Lhonak Complex, a detailed project report is being developed by the Central Water Commission in collaboration with the Sikkim government for a flood-retention structure at Dolma Sampa near Muguthang, according to PTI. In the Gurudongmar Complex, authorities are proposing the construction of a moraine plug wall at the lake’s outlet, considering the area’s cultural and religious significance in their plans.
Officials have emphasized that there is no universal solution applicable to all lakes. Various strategies under consideration include water drainage and pumping, enhancement or construction of drainage channels, rock mass reduction with safety walls, and the creation of tunnels to lower lake levels.
In February 2025, Sikkim’s Department of Science and Technology was appointed as the leading agency for GLOF hazard evaluations and mitigation research. The state is also in the process of developing what could become India’s first dedicated GLOF Risk Mitigation Protocol, which aims to create a standardized approach for assessing, preparing for, and mitigating the risks associated with glacial floods.
This proposed protocol may serve as a benchmark for other regions in the Himalayas, as indicated by state officials.
Field investigations will include monitoring water levels and discharge from the lakes, conducting geophysical surveys, bathymetric studies, flood modeling, and hazard assessments. Additionally, researchers will evaluate the feasibility of reducing lake levels and constructing flood-retention structures.
Officials have also highlighted the necessity of enhancing early-warning systems. Following discussions with Union Home Secretary Govind Mohan, the introduction of additional sensors in Sikkim has been proposed, and he provided a favorable response to this initiative.
Mohan reviewed the preparedness of various Himalayan states and Union Territories in terms of GLOFs and snow avalanches. The meeting was attended by senior officials from Sikkim, Uttarakhand, Himachal Pradesh, Arunachal Pradesh, Jammu and Kashmir, along with representatives from the Ministry of Home Affairs, the National Disaster Management Authority, the Central Water Commission, the India Meteorological Department, and the Defence Geoinformatics Research Establishment.
