A satellite-based assessment of five glacial lakes in Arunachal Pradesh’s Tawang district has found that four have expanded over the last decade, with one lake showing particularly rapid growth, adding fresh evidence to concerns over the threat posed by glacial lake outburst floods (GLOFs) in the eastern Himalaya.

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

The assessment comes amid heightened attention on glacial hazards in the region following a recent risk evaluation by the Centre for Earth Sciences and Himalayan Studies (CESHS), Arunachal Pradesh, and broader efforts by authorities to identify potentially dangerous glacial lakes in the Himalaya.

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

Among the lakes analysed, Sanhapo Lake showed the most significant growth. Suhora estimated its area at 78.07 hectares in 2019, increasing to 88.81 hectares by mid-June 2026. The company said that while uncertainties remain regarding its historical extent because of ice cover visible in 2016 imagery, the lake has exhibited sustained expansion in recent years. Given its size and continued growth, Suhora identified it as the highest-priority lake among those assessed for detailed hazard modelling, continuous monitoring and possible early-warning systems.

The remaining lakes showed more modest changes. Two lakes categorised by the NDMA as “very high risk” expanded by about a hectare over the decade, while Dharkha Tso, listed as “high risk”, also recorded gradual growth. A fifth lake remained broadly stable over the observation period.

Commenting on the findings, Amit Kumar, co-founder and chief operating officer of Suhora Technologies, said satellite observations were increasingly important for monitoring remote mountain regions where field access was often difficult. “By comparing satellite imagery across multiple years, it is possible to track changes in glacial lake extent with the monsoon season approaching, continuous observation of glacial lakes becomes increasingly important”, he added.

Anil Kulkarni, glaciologist and distinguished fellow at the Divecha Centre for Climate Change, Indian Institute of Science, Bangalore and who wasn’t connected to the study, said the observed expansion warranted attention but should not be interpreted as evidence of an impending disaster.

“If lakes are expanding, then it is considered as an unstable lake,” he said. However, he stressed that the key question was why a lake was growing. Lakes impounded by moraines — ridges of rock and debris deposited by glaciers — can become hazardous when retreating glaciers increase the volume of water trapped behind them. Yet several other factors determine risk, including the possibility of landslides, avalanches or rockfalls entering the lake and the extent of downstream exposure.

“Mere increase in area, even over a decade, cannot be a single criterion” for judging how dangerous a lake is, Mr. Kulkarni told The Hindu. “It can be a concern, but how risky it is, we do not know.”

Worries over Himalayan glacial hazards have intensified since the October 2023 disaster in Sikkim, when a breach associated with South Lhonak Lake triggered floods that killed dozens of people and destroyed the Chungthang hydropower dam. GLOFs can occur when natural moraine dams fail or when large avalanches, landslides or icefalls suddenly displace water and generate destructive waves.

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

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

“The question is, once we identify this is a problem, how are we going to resolve it? How can we reduce the risk to mountain communities or infrastructure?” he said. “That is where we really are lacking.”