Glacial lakes in India’s northern Himalayas are expanding at an alarming rate, with dozens of new ones forming in just the past two decades, according to a new study. Researchers warn that many of these lakes could burst without warning, flooding valleys where thousands of people live.
The study focused on the Alaknanda Basin in the Garhwal Himalayas, part of the Upper Ganga river system. Scientists used satellite images stretching back to 1994 to track how the region’s glacial lakes have changed over nearly 30 years.
They found that the area covered by the basin’s larger lakes grew by about 67% between 1994 and 2023. Even more concerning, 57 brand-new lakes appeared over that period, bringing the basin’s total to 131. Eighteen of those new lakes are big enough to matter — and 42 lakes in the basin are now larger than 0.01 square kilometres.
Two lakes stood out for their dramatic growth. Vasundhara Lake, high in the mountains at 4,677 metres, has more than tripled in size since 1994. Balbala Lake, which sits upstream of the important pilgrimage site Badrinath, grew by 119% over the same period. Looking further back, researchers found Balbala Lake barely existed in 1980 yet by 2023 it had grown by more than 800%.
The problem isn’t just that the lakes are getting bigger. The research warns that many of these lakes could pose a serious threat to downstream communities through glacial lake outburst floods (GLOFs).
These lakes often form behind dams made of loose rock, gravel and sand left behind by retreating glaciers. Such dams are unstable. If they fail, because of an avalanche, an earthquake, heavy rain or simply too much water pressure, the lake can empty catastrophically, sending a wall of water, mud and debris rushing downstream.
The catastrophic events in Nepal were not technically caused by a GLOF, but study author Dr Aayushi Pandey from Charles University, Prague, explained: ‘The recent flooding is a reminder of how important it is to continuously monitor high-mountain environments where multiple hazards including extreme rainfall, glacial lake expansion, slope instability and seismic activity can interact and potentially amplify downstream impacts.’
The study looked closely at Balbala Lake and rated its risk of bursting as ‘very high.’ A field visit in 2019 confirmed why: the lake is surrounded by steep slopes over 45 degrees, chunks of ice are constantly breaking off the glacier and falling in, and rocks and debris are piling up inside the lake. Its outlet is made of soft, loose soil that could give way quickly during extreme weather.
Many of the fastest-growing lakes sit near the Rattakona and Mana regions. Because they’re so close together, researchers worry they could merge, making any future flood even bigger and more destructive.
The region is already on edge. The Alaknanda Basin is seismically active and home to dozens of hydroelectric dams, either operating or under construction. In 2013, the Kedarnath disaster, which was triggered by heavy rain and a glacial lake outburst, killed thousands of people and destroyed entire villages.
The study identified 27 lakes that need continuous monitoring, including 18 that formed in the last two decades and nine that are growing rapidly. The authors are calling for detailed stability checks, early warning systems and, where possible, controlled lowering of water levels in the most dangerous lakes.
They also express concern that small lakes are often left out of official hazard maps because they fall below size thresholds. But recent events in the Himalayas have shown that even tiny lakes can cause deadly floods.
Dr Pandey said: ‘Satellite data are extremely valuable for screening a large and inaccessible region. They allow us to identify newly formed lakes, measure changes in lake area, identify rapidly expanding lakes and shortlist those that need detailed investigation. But that’s not the complete solution. Field measurements are essential to determine lake depth and volume, assess slope stability, understand drainage pathways and glacier–lake interactions, and improve flood modelling.
‘But this work requires substantial logistical and financial support, including stronger transboundary scientific cooperation and data sharing, because glacial-lake and flood hazards do not follow political boundaries and should be addressed as a shared regional concern.’
Photo: Gurdeep singh