A reported glacial lake outburst flood (GLOF) at Sintaphu Lake in northern Bhutan has swept away Gasa Tshachu hot spring complex and damaged Punakha-Gasa highway, prompting authorities in the downstream Indian states of Assam and West Bengal to go on high alert for a possible rise in Sankosh river.
According to Daily Bhutan, authorities are working out the full extent of the damage following the incident on Thursday evening.
The outburst took place near Wakila Mountain in Lungo, Laya Gewog, within Gasa. Floodwaters reached Taktsemakhang around 8.15pm on Thursday, damaging a section of the road to Laya, one of Bhutan’s most remote highland communities, and forcing its closure.
On Friday, Daily Bhutan reported that the floodwaters had swept away hot spring complex beside Mo Chhu river.
A section of Punakha-Gasa Secondary National Highway near 31.85-kilometre point was completely washed away, leaving the road closed to all traffic until further notice. Travellers have been advised to put off non-essential journeys or confirm alternative arrangements before setting out.
Precautionary evacuations were carried out in exposed locations, and warning sirens were sounded.
As of Friday morning, no deaths or injuries had been reported. The cause of water release, volume of water, and full extent of the damage are not yet confirmed.
A glacial lake outburst flood occurs when water stored in a glacial lake is suddenly released, often because natural barriers called moraines are breached or weakened.
The resulting flood can race through mountain valleys, carrying mud, rocks, and debris, and damaging roads, bridges, and settlements.
Sintaphu is a high-altitude glacial lake at the headwaters of Mo Chhu and appears on Bhutan’s official list of 17 potentially dangerous glacial lakes. The listing signifies that a lake requires continued monitoring, not that an outburst is certain.
Bhutanese specialists studied Sintaphu between May and June 2023, measuring the main and upper lakes, examining the surrounding terrain and moraine barriers, and monitoring the feeding glacier.
Monitoring equipment has since been installed in the area.
Water from Sintaphu flows into Mo Chhu, which runs south through Gasa and Punakha. At Punakha, Mo Chhu meets Pho Chhu to form Punatsangchhu, which later enters India as Sankosh river.
India’s Central Water Commission (CWC) issued a special flood advisory for West Bengal and Assam on Thursday.
The advisory stated that the outburst had been reported by the Indian Embassy in Bhutan and warned that a flash flood in the upper reaches of Punatsangchhu (known as the Sankosh in India) could cause a sudden rise in water levels downstream in Alipurduar district in West Bengal and Dhubri district in Assam.
Local authorities along the river were instructed to stay alert, monitor the situation closely, and take necessary precautions.
Assam Chief Minister Himanta Biswa Sarma said on Friday that the state government was closely monitoring the potential impact across vulnerable revenue circles of Dhubri and Kokrajhar districts, with disaster response teams and other agencies on standby. Writing on social media platform X, Sarma noted that state teams are in constant contact with the National Disaster Response Force (NDRF) and other agencies, adding, “Residents are requested to stay alert, follow official updates and cooperate with local officials”.
According to the Assam State Disaster Management Authority, no evacuation had started in Dhubri or other districts of Lower Assam as of Friday, but district administrations and State Disaster Response Force (SDRF) teams are prepared to respond to any emergency. Water levels in Assam’s rivers have not risen so far, and the situation remains under watch.
In Siliguri, West Bengal Tourism Minister Sankar Ghosh confirmed that the state administration was on high alert and ready to deal with any emergency, noting that no devastating incident had been reported in Alipurduar so far.
Precautionary advisories have been issued, and officials are closely monitoring the situation.
Communities along Sankosh river and its tributaries in North Bengal have been advised to move to safer locations.
