Bhutan glacial lake flood: Satellite reveals what happened after the outburst

One lake had expanded steadily for a decade before the disaster. New satellite analysis shows what happened after the flood.

A satellite-based assessment of Bhutan’s Sintaphu Tsho lake has revealed that its surface area shrank by approximately 73 per cent following a Glacial Lake Outburst Flood (GLOF) on October 29, 2026, highlighting the scale of water loss triggered by the disaster.

The assessment, conducted by Noida-based geospatial intelligence company Suhora Technologies, also found that a nearby supraglacial lake had shrunk by 24.4 per cent following the event.

The GLOF struck Sintaphu Tsho in Bhutan’s Gasa district, destroying facilities at Gasa Tshachu, a popular natural hot spring along the Mo Chhu River.

The flash flood has also raised concerns in India, prompting authorities to issue flood alerts in parts of West Bengal and Assam over a possible surge in the Sankosh River.

For its assessment, Suhora analysed high-resolution, one-metre Synthetic Aperture Radar (SAR) satellite imagery acquired on October 30, 2026, providing a near-real-time picture of changes in the lake system.

According to the findings, Sintaphu Tsho’s surface area fell from 24.13 hectares to 6.54 hectares, a reduction of nearly three-fourths. The adjoining supraglacial lake shrank from 16.50 hectares to 12.47 hectares.

A DECADE OF CONTRASTING CHANGES

A GLOF occurs when water stored in a lake formed by melting glaciers is suddenly released. This can happen when a natural barrier holding the water fails or is breached.

The resulting surge can travel rapidly through mountain valleys. It can carry large amounts of debris and damage settlements, roads, bridges and farmland.

Suhora's analysis of satellite imagery from 2016 to 2026 revealed contrasting trends in the two water bodies before the outburst.

Sintaphu Tsho remained relatively stable over the decade, growing marginally from 23.33 hectares in 2016 to 24.13 hectares in 2026. However, it reached its largest recorded extent on October 28, just a day before the GLOF.

In contrast, the supraglacial lake expanded steadily from 5.74 hectares in 2016 to 16.51 hectares in 2026, an increase of nearly 188 per cent. It gained approximately 1.1 hectares annually without recording a year of decline.

Despite shrinking after the outburst, the supraglacial lake remains more than twice its 2016 size.

Suhora CEO and co-founder Krishanu Acharya said the findings underline the importance of continuous monitoring of glacial lakes and satellite-based Earth observation in strengthening disaster preparedness across vulnerable Himalayan regions.

The assessment used Suhora's SID platform, which automatically selects suitable satellite imagery based on prevailing weather conditions, enabling monitoring even under cloudy skies.

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