How Did the Flash Floods Unfold in Sikkim? ISRO's Satellite Images Explain

Take a look at the temporal satellite images captured by ISRO's radar satellite RISAT 1A.

Massive flash floods hit the northeastern state of Sikkim on Wednesday, 5 October, causing massive destruction with at least 14 people declared dead, and over 100 missing. Several reports state the floods unfolded after a cloud burst over the South Lhonak Lake in northern Sikkim.

(Photo: X/@iambhutia)

Devastating flash floods hit the northeastern state of Sikkim on Wednesday, 5 October, with at least 14 people dead and over 100 more missing.

But what exactly triggered the floods? The National Remote Sensing Centre, a unit of the Indian Space Research Organisation (ISRO), conducted a satellite-based study on the 'Outburst of the South Lhonak Lake' in Sikkim.

The study was conducted on the basis of before-and-after images which shows that the South Lhonak Lake was drained of vast volumes of water that flowed downstream into the Teesta River, and in turn, flooded low-lying areas.

Here's what the ISRO study reveals.

These satellite images depict the South Lhonak Lake area to be around 162.7 Hectares on 17 September, and 167.4 Hectares approximately, at 6 pm on 28 September.

It also shows the lake area at around 60.3 Hectares approximately, at 6 am on 4 October.

"It is observed that Lake is Burst and about 105 Hectares area has been drained out (28 September 2023 image versus 04 October 2023) which might have created a flash flood downstream," ISRO wrote on its website.

The country's space agency added that it will continue monitoring the lake by further using satellite data.

'A Combination of Rainfall & GLOF': NDMA

Meanwhile, the National Disaster Management Authority (NDMA) has also provided a brief explanation: "In the early hours of Wednesday, there was a sudden surge in water flow in the Teesta river, which washed away several bridges, parts of NH-10, the Chungthang Dam and has impacted several small villages, towns and infrastructure projects in the upper reaches of the river valley."

"The primary reason for sudden surge appears to be a likely combination of excess rainfall and the Glacial Lake Outburst Flood (GLOF) event at the South Lhonak Lake in North Sikkim," it added.