GUWAHATI, Sept 11: Arunachal Pradesh has 197 expanding glacial lakes, including 32 classified as high risk and requiring active mitigation, raising concerns over potential glacial lake outburst floods (GLOFs) in downstream river systems in Assam and Bhutan, according to river expert Prof Nayan Sarma.
Sarma told The Assam Tribune that Arunachal Pradesh and Bhutan, located in the highly vulnerable Eastern Himalayas, are witnessing rapid glacier melt that is creating and expanding unstable proglacial lakes.
Among the river systems considered vulnerable to GLOF events are the Tawang Chu, also known as Mago Chu, and the Dibang in Arunachal Pradesh, as well as the Punatsang Chhu and Kuri Chu in Bhutan.
The Kameng Chu in Tawang district is also considered vulnerable because of the rapidly melting Khangri glacier. The river is known as the Jia Bharali in Assam.
Scientists have identified unstable proglacial lakes at an altitude of around 16,500 feet near the Khangri glacier. According to Sarma, high-risk lakes in the Mago Chu basin have expanded significantly over the past decade, prompting their classification as potentially dangerous by the National Disaster Management Authority.
Satellite analysis in 2026 showed that Sanhapo Glacial Lake in the Mago Chu basin expanded from 56 hectares in 2016 to 89 hectares. The increase has heightened concerns over the possibility of a GLOF originating in the basin.
Bhutan also faces significant GLOF risks. The Punatsang Chhu Basin has experienced major glacial lake outburst events in the past, including the 1994 Lugge Tsho outburst. Thorthormi Tsho is among the high hazard glacial lakes that continue to be closely watched.
The Punatsang Chhu, which supports two hydropower dams in Bhutan, is known as the Sankosh River in Assam. Bhutan’s northern glaciers feed seven major river systems: Amo Chu, Wang Chu, Punatsang Chhu, Mangde Chu, Chamkhar Chu, Kuri Chu and Drangme Chu.
Hydropower generated from these river systems contributes around 40 per cent of Bhutan’s national revenue, with a substantial share of electricity exported to India.
The Kuri Chu and Drangme Chu from Bhutan, along with the Tawang Chu from Arunachal Pradesh, eventually join the Manas River in Assam. Any major GLOF propagating through these high altitude river systems could therefore have implications for downstream areas in Assam.
Sarma said effective GLOF risk reduction requires an integrated monitoring system combining real time satellite technology, field sensors and structural engineering measures.
He stressed the need for high-resolution satellite imagery and Interferometric Synthetic Aperture Radar (InSAR) to monitor changes in expanding glacial lakes and identify signs of instability in moraine dams.
Synthetic Aperture Radar (SAR), he said, is particularly useful because it can monitor glacial and terrain deformation through cloud cover and during periods of darkness, making it valuable for monitoring during storms and the long winter months.
Automated Weather Stations powered by solar energy could also be deployed near high risk lakes to monitor changes in temperature, weather conditions and water levels.
The growing number and size of glacial lakes in the Eastern Himalayas underline the need for continuous monitoring and early warning systems, particularly because several vulnerable river systems flow from the high mountains into densely populated downstream regions of Assam.