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An earthquake that originated in Nepal on the intervening night of October 3 and October 4, 2023 might have triggered the bursting of the South Lhonak Lake, according to sources in the India Meteorological Department. The lake had already become vulnerable over the last 11 days with unusual expansion, they pointed out.
Water from over 100 hectares of the lake gushed downstream, according to an estimate prepared by the Disaster Management Support Group under National Remote Sensing Centre, the Indian Space Research Organisation. This gushing stream joined forces with water already accumulated in the Chungthang dam, causing it to collapse partially, confirmed sources in Sikkim.
The release from the dam multiplied the impact and triggered severe devastation in Sikkim and also in West Bengal.
Jairam Ramesh, congress leader and former environment minister of India, flagged the need to have credible environment impact assessments before allowing hydel dams to be set up at the wake of the latest disaster; echoing a demand the environmentalists have been making for a long time.
“It is another reminder of how we must learn to be more sensitive to local ecologies while planning for and executing hydel projects especially in fragile areas,” Ramesh told Down To Earth and reiterated on the microblogging site X (formerly known as Twitter).
“As environment minister, I always insisted on cumulative, comprehensive and credible environment impact assessments before embarking on building dams,” he added. “But we never seem to learn.”
“Most of the hydel dams, the way they have been constructed and operate holding water for most of the time to maximise profit though they are officially supposed to be run of the river dams, are a recipe for disaster and Chungthang collapse has given us another reminder,” said an environmentalist in Bengal.
On Thursday, as the water started to recede in Teesta, dead bodies were recovered from several places in north Bengal, pointed out sources in local administration. Overall, till October 6, the toll due to the Teesta flash flood was 40, according to news agency Reuters, and more than 100 persons are reported to be missing, including 22 army personnel.
Several are being treated in various hospitals, while a few thousand tourists and locals have reportedly been stranded, especially in between Lachen valley and Chungthang.
The status of the region is still unknown because it has been cut off following the collapse of 19 bridges, making it difficult for the disaster management teams to reach.
“Poor weather also held back helicopter operation,” pointed out an official, indicating that the actual losses may be much higher.
Multiple factors acted in tandem to trigger the bursting of the lake around Tuesday midnight and magnifying the disaster, but the final trigger seems to have been an earthquake that occurred near Chaukham in Nepal, about 765 km away from South Lhonak lake, experts surmised.
“A minor earthquake of 3.1 magnitude on the Richter scale occurred at the stroke of midnight in Nepal, followed by another one of intensity 3.7 at 12.35 am in the same place (29.51, 80.71 lat-long) seemed to have triggered the bursting of the glacial lake as it collapsed around that time,” according to an IMD expert. There was another minor earthquake at 1.53 am, they added.
Unusually high rainfall, a tell-tale example of heightening climate change impact, also could have contributed, said experts.
“Intense rain has led to this catastrophic situation in Sikkim, triggering a glacial lake outburst flood. We observe that such extreme events increase in frequency as the climate continues to warm and takes us into unknown territories,” pointed out Miriam Jackson, senior specialist of ICIMOD.
Arun B Shrestha, senior climate change specialist from ICIMOD working in the region, said,“This seems like another unfortunate example of cascading hazards. We have recorded exceedingly high precipitation of more than 100 millimetres within the last 24 hours in the vicinity”.
ISRO data indicated that the lake was rapidly turning vulnerable in the last few days. “If you look at the ISRO data, you will find that on September 17, its size was 162.7 hectares approximately. This increased to 167.4 ha approximately on September 28 – an almost 3 per cent rise within 11 days. This was clearly a signal and an early warning could have saved many lives,” pointed out environmentalist Animesh Bose of non-profit Himalayan Nature & Adventure Foundation.
A team from the National Disaster Management Authority along with other experts camped in the second and third week of September to observe the lake condition.
Eight bodies have been found from Mainaguri in Jalpaiguri, while a body was found floating in Fulbari canal, according to local administration in north Bengal. Two labourers have been found missing in a tea garden in Jalpaiguri while two bodies were found floating in Gajoldoba Teesta barrage. The sources pointed out that the possibility of finding the missing persons has been steadily decreasing with time.
At least five tourists have been reported to be missing so far, two from New Delhi and three from West Bengal’s Uttar Dinajpur district, while around 3,000 tourists have been reportedly stranded in the area.
Bengal chief minister Mamata Banerjee has already asked the chief secretary to make arrangements to rescue locals and tourists, and a team of ministers and senior officers has been rushed to north Bengal.
“We were extremely concerned about the flood risk of thousands living in Padamati village area within Nandapur Gram Panchayat, a char area (land formed by silt accumulation) downstream to Gajaldoba barrage, but fortunately the water-level started to recede from the afternoon of Wednesday and there has been no fresh cause of concern today, as the rain also relented to an extent,” pointed out Arnab Bhatacharya from the nonprofit NESPON working in the area.
“We expect the rain to subside from tomorrow,” said GK Das, head of IMD Alipore weather section, on October 5, 2023.