Four out of five high-risk glacial lakes in Arunachal expanding over decades, satellite study finds

A satellite assessment of five glacial lakes in Arunachal Pradesh’s Tawang district has found that four have expanded over the past decade, with one lake showing particularly rapid growth, adding new evidence to concerns about the threat posed by Glacial Lake Flooding (GLOF) in the eastern Himalayas.

The analysis — a report, not a peer-reviewed study — by Noida-based geospatial intelligence firm Suhora Technologies examined five lakes in the Mago Chu basin that were classified as “high risk” or “very high risk” by the National Disaster Management Authority (NDMA).

The assessment comes amid heightened attention to glacial hazards in the region following a recent risk assessment by the Center for Earth Sciences and Himalayan Studies (CESHS), Arunachal Pradesh and a wider effort by authorities to identify potentially dangerous glacial lakes in the Himalayas.

Using images from the ICEYE, PlanetScope and LISS-IV satellites, Suhora compared the extent of the lakes between 2016 and June 2026. In a press release accompanying the analysis, the company said that “four of the five lakes have expanded, reflecting the general trend of glacier retreat and meltwater storage.” But it cautioned that “lake expansion does not directly indicate a flood” and said the findings instead highlighted “the importance of regular monitoring and further assessment to better understand future risks”.

Among the lakes analyzed, Lake Sanhapo showed the most significant growth. Suhora estimated its area to be 78.07 hectares in 2019, increasing to 88.81 hectares by mid-June 2026. The company said that while there remain uncertainties about its historical extent due to the ice cover visible in the 2016 images, the lake has shown a steady expansion in recent years. Due to its size and continued growth, Suhora identified it as the highest priority lake among those evaluated for detailed hazard modeling, continuous monitoring and possible early warning systems.

The remaining lakes showed milder changes. The two lakes categorized as ‘very high risk’ by the NDMA have expanded by about a hectare over the decade, while Dharkha Tso, classified as ‘high risk’, has also seen gradual growth. The fifth lake remained more or less stable during the observation period.

Commenting on the findings, Amit Kumar, co-founder and chief operating officer of Suhora Technologies, said satellite observations are increasingly important for monitoring remote mountainous areas where access to the terrain has often been difficult. “By comparing satellite images over several years, it is possible to monitor changes in the extent of glacial lakes as the monsoon season approaches, continuous observation of glacial lakes becomes increasingly important,” he added.

Anil Kulkarni, a glaciologist and senior fellow at the Divecha Center for Climate Change, Indian Institute of Science, Bangalore, who was not associated with the study, said the observed expansion is noteworthy but should not be interpreted as evidence of impending disaster.

“If the lakes are expanding, then it’s considered an unstable lake,” he said. But he stressed that the key question is why the lake is growing. Lakes flooded by moraines—ridges of rock and debris deposited by glaciers—can become dangerous when retreating glaciers increase the volume of water trapped behind them. Several other factors determine the risk, including the possibility of landslides, avalanches, or rock falls entering the lake and the extent of exposure downstream.

“Mere increase in area, even in ten years, cannot be the only criterion” to judge how dangerous the lake is, Kulkarni told The Hindu. “It might be worrying, but we don’t know how risky it is.

Concerns about Himalayan glacier dangers have intensified since the October 2023 Sikkim disaster, when a breach linked to South Lhonak Lake triggered floods that killed dozens of people and destroyed the Chungthang hydroelectric dam. GLOFs can occur when natural moraine levees fail or when large avalanches, landslides, or icefalls suddenly displace water and create destructive waves.

Following the Sikkim disaster, the NDMA approved the National Glacial Lake Outburst Flood Mitigation Program and identified 189 high-risk glacial lakes for monitoring and mitigation. The program includes detailed hazard assessments, installation of automated weather and water level monitoring systems, early warning networks and, where possible, lake level lowering measures to reduce the risk of flooding. The Central Water Commission said that more than 900 glacial lakes and bodies of water are currently being monitored through satellite observations.

Mr Kulkarni said India’s ability to identify potentially dangerous glacial lakes had improved greatly through satellite monitoring and modelling. However, he argued that translating scientific assessments into practical risk reduction remains a major challenge.

“The question is, once we know it’s a problem, how do we fix it? How can we reduce the risk to mountain communities or infrastructure?” he said. “That’s what we’re really missing.

Published – 19 Jun 2026 21:59 IST