Sikkim: ISRO's Image-Based Studies Of Lhonak Lake Reveal What Caused Flash Floods

Temporal satellite images released Wednesday evening by ISRO show changes in the volume of water in Sikkim's Lhonak Lake.

Temporal satellite images released Wednesday evening by ISRO show changes in the volume of water in Sikkim's Lhonak Lake. ( Image Source :www.isro.gov.in )

The National Remote Sensing Centre, one of the ISRO centres, has carried out a satellite-based study on the outburst of the South Lhonak lake in Sikkim by obtaining temporal satellite images (before and after) over the water body. According to ISRO, about 105 hectares of area, which is nearly 65 per cent of Lhonak Lake, has been drained out.

"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," an ISRO statement said on Wednesday. The space agency said it will continue monitoring the lake further using the satellite data.

An image captured on Wednesday morning at 6 AM after the cloudburst and flash flood wreaked havoc in the state shows the lake reduced by more than half and with only an estimated 60.3 hectares of water in it.

At least 10 people were killed, and 82 others, including 22 army personnel, are still missing, as a result of a devastating flash flood caused by a cloudburst over Lhonak Lake in north Sikkim in the early hours of Wednesday (October 4). Three of the bodies were discovered in north Bengal. In addition, one of the 23 army personnel reported missing earlier in the day has been found. The flood, which began around 1:30 AM, was exacerbated by the release of water from the Chungthang dam, news agency PTI reported citing officials.

The Sikkim government declared the natural disaster a state of calamity through an official notification. The surge in water flow from the Teesta River resulted in extensive damage, including the destruction of bridges, sections of NH-10, and the Chungthang Dam. Multiple small villages, towns, and infrastructure projects in the upper reaches of the river valley were affected, particularly major districts like Mangan, Gangtok, Pakyong, and Namchi.

The Dalai Lama, Tibet's spiritual leader, expressed his solidarity with the people of Sikkim. The Tibetan spiritual leader, who has hundreds of thousands of followers in the Himalayan state, expressed solidarity in a letter to Sikkim Chief Minister Prem Singh Tamang.

The National Disaster Management Authority (NDMA) attributed the primary causes of the flash floods in Sikkim to a combination of excess rainfall and a Glacial Lake Outburst Flood (GLOF) event at the South Lhonak lake in north Sikkim. Concerns were raised about the vulnerability of approximately 25 glacial lakes in Sikkim to such events.