Glacial lake outburst in Bhutan prompts flood alerts in Indian states

A glacial lake outburst flood (GLOF) from Sintaphu Lake in Bhutan's Gasa district triggered downstream alerts in India's West Bengal and Assam on October 29. The surge of water damaged roads and bridges in Bhutan's remote Laya community and washed away the Gasa Tshachu hot spring complex, while the Punakha-Gasa highway also suffered damage.

Indian authorities, alerted by the Indian Embassy in Bhutan, issued a special advisory through the Central Water Commission. More than 10,000 residents in West Bengal's Alipurduar district were moved to safer locations, and vulnerable areas in Assam's Dhubri and Kokrajhar districts remain under close observation as the Sankosh River could rise.

As of Friday afternoon, no deaths or injuries have been reported.

The Kathmandu-based intergovernmental body ICIMOD, which monitors Himalayan environmental risks, said the incident is part of a growing pattern of mountain hazards across the region. It noted that Sintaphu Lake holds an estimated 6-7 million cubic metres of water, roughly the volume of 2,400–2,800 Olympic-size swimming pools, and that the exact amount released is still being evaluated.

"The timely warnings issued by Bhutan's authorities illustrate the importance of sustained monitoring and effective early warning systems in reducing disaster risk," said Pema Gyamtsho, Director General of ICIMOD. "As mountain hazards become more complex, continued investment in forecasting, preparedness, and cross-border cooperation will be essential to protecting vulnerable communities throughout the Himalaya."

The event follows recent mountain disasters in Nepal, including a rock-ice avalanche in August and a flash flood in late October, underscoring the need for coordinated transboundary disaster management. Bhutan’s National Centre for Hydrology and Meteorology continues to monitor potentially dangerous glacial lakes, many of which are held back by unstable moraines.