Oct 06 – On Wednesday, a catastrophic flash flood struck Sikkim, triggered by a sudden glacial lake burst, resulting in multiple casualties and widespread destruction. The torrential rain caused the Teesta River to surge uncontrollably, and it led to the significant loss of the state’s largest hydropower project, Sikkim Urja, worsening the crisis.
Rescue efforts have been hampered by mudslides, washed-out roads, and damaged communication systems.
The cloudburst was exceptionally intense, causing the lake to overflow rapidly beyond its capacity. The region received an unprecedented fivefold increase in its usual rainfall. This cloudburst, combined with the melting of the Lhonak Glacier, triggered a Glacier Lake outburst flood (GLOF), resulting in the sudden release of an enormous volume of water.
Lhonak Lake, situated in the remote northwestern part of Sikkim at an altitude of 17,100 feet, formed due to the melting of Himalayan glaciers.
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Authorities issued warnings as the water levels rose, but at around 1 am, the Teesta Stage 3 dam, known as the Urja project, was washed away by the flash flood, thwarting evacuation plans for nearby residents.
The Urja dam, situated 5,000 feet above sea level in Chungthang, and a 200-meter-long bridge connecting to the powerhouse were swept away, with the entire powerhouse submerged in the deluge. Expert assessments indicate that the Teesta’s water level was below the danger threshold before the dam’s breach.
Downstream of the Teesta River, massive devastation occurred, including damaged houses and buildings, washed-out roads, and the collapse of at least 11 bridges.
Several areas, including Mangan, Dikchu, Singtam, Rangpo, Chungthang, and Bardang, were severely affected.
Satellite images of the glacial lake revealed that nearly 65 percent of its water surged into the Teesta River.
As for the cause of the lake breach, the primary trigger was the cloudburst, where more than 10 centimeters of rainfall occurred within a 10-square-kilometer area in just an hour.
Additionally, scientists have pointed to the possibility of an avalanche. The lake’s banks might have ruptured when ice chunks fell into the water, generating powerful waves within the lake. Jakob F Steiner, a senior scientist, noted the presence of ice patches on the lake’s surface in satellite images, suggesting that “a chunk of either ice or unstable slopes has detached and dropped into the lake water.” Such an event could create shockwaves across the water surface sufficient to breach the lake’s dam.
