40 high-hazard glacial lakes identified in Sikkim, 16 at highest risk of outburst

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 data is significant as it comes against the backdrop of the recent flash floods in Nepal, triggered by a glacial collapse near the Nepal-Tibet border on 26 August that left a trail of destruction with hundreds of people dead and scores missing.

Though the catastrophe was not linked to a glacial lake outburst flood (GLOF), the flash floods highlighted a broader transformation across the Himalayas as glaciers retreat, new lakes are form in their place, and existing ones expand.

Glacial lakes are formed by the melting of glaciers and accumulation of meltwater in depressions on or near the glacier's surface. GLOFs occur when these lakes suddenly burst open due to factors such as excessive water accumulation or triggers like earthquakes, and can cause significant destruction and pose serious risks to people and the environment downstream.

One such outburst in Sikkim in October 2023 resulted in at least 60 fatalities and extensive damage in Mangan, Gangtok, Pakyong and Namchi districts.

At a recent media sensitisation workshop on GLOF risk mitigation in Gangtok, principal secretary Sandeep Tambe said remote sensing and satellite imagery were being used to monitor changes in glacial lakes. Of the 40 high-hazard lakes, 16 are in Category A (highest risk), two in Category B (high risk) and nine in Category C (moderate to low risk), while 13 remain unclassified, he said.

Sikkim's department of science and technology was designated the nodal department for GLOF hazard assessment and mitigation studies in February 2025, with the work being carried out through an interdisciplinary approach, Tamang said.

The state is also working towards what could be the country's first dedicated GLOF risk mitigation protocol, aimed at creating a standardised scientific framework for assessing, preparing for and mitigating glacial flood risks.

It could also serve as a model for other Himalayan regions.

With agency inputs