Flash flood threat looms over Bengal, Assam after glacial lake outburst in Bhutan

A glacial lake outburst in northwestern Bhutan has triggered concerns over possible flash floods in parts of West Bengal and Assam, with authorities in both states issuing alerts for vulnerable areas.

The incident occurred at Shintaphu Lake in Bhutan's Gasa district on Thursday evening, sending a surge of water down the Mo Chhu River. The resulting flood completely washed away facilities at Gasa Tshachu, a popular natural hot spring situated along the riverbank. No casualties have been reported, as the area had been evacuated before the incident.

Shintaphu Lake, located at the source of the Mo Chhu, is among Bhutan's 17 glacial lakes identified as potentially dangerous. Gasa Tshachu had also suffered extensive damage during a flash flood on August 26, 2021, when the swollen river changed its course towards the hot spring.

Bengal, Assam districts on alert

The floodwater has crossed Srigang in Kabesa Gewog and is now around eight kilometres from Punakha Dzong. Bhutan has alerted the governments of West Bengal and Assam, warning of potential flooding in areas bordering the country.

Assam's Dhubri and West Bengal's Darjeeling hills, Alipurduar and Jalpaiguri are among the areas considered vulnerable.

In Cooch Behar, the district administration has cautioned residents living along the Sankosh River, which originates in northern Bhutan before flowing into the Brahmaputra in Assam.

Appealing to residents not to panic, Alipurduar Police District SP Amit Kumar Shaw said, "My appeal to everyone is that there is no need to panic in any way," He added, "We are in alert mode, the administration is fully prompt, and all agencies are actively working, so there is no issue. We hope that within two to three hours, we will reach a resolution and address whatever trouble the public is facing..."

Irrigation project damaged in Bhutan

The flash flood has also affected infrastructure in Bhutan. The Solar Irrigation Lifting System, installed earlier this year in the Dochhukha-Dzomlingthang-Ritsa Chiwog area under Guma Gewog in Punakha, has suffered partial damage.

A local leader said the system had stopped functioning, although the extent of the damage is yet to be assessed. Flood-borne debris has also covered a section of the Punakha-Gasa Highway near Dzomlingthang.

What is a glacial lake outburst flood?

A glacial lake outburst flood (GLOF) occurs when water accumulated in a lake formed by retreating glaciers is suddenly released after the natural dam holding it gives way.

Rising temperatures linked to human-caused climate change have accelerated glacier retreat, contributing to the formation and expansion of such lakes. Heavy rainfall, landslides, avalanches, earthquakes and rapid glacier melt can trigger a breach, unleashing large volumes of water downstream.