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are Possible reasons for the Sikkim flood disaster on October 4, 2023 could include


lood damage in Rangpo caused by the Sikkim flood. Image by Praful Rao of Save the Hills.

The author of The Landslide Blog is Dave Petley, a renowned expert in the field of landslide research and control.

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Amid a flood of devastating news, the devastating flood in Sikkim, located in Northeast India, on October 4, 2023, has been largely overlooked. The main details of the incident have now been clarified – a significant Glacial Lake Outburst Flood (GLOF) occurred at South Lhonak, rushing down the Teesta River towards the Teesta III hydroelectric dam in Chungthang. The dam was quickly overtaken and ultimately gave way, resulting in a catastrophic flood that has resulted in numerous casualties downstream, with at least 40 reported deaths.

Yesterday, Praful Rao shared a series of photos on the highly-regarded Save the Hills blog depicting the extent of damage caused by the recent floods. One of the images illustrates the depth to which properties in Rangpo have been submerged.

Flood damage in Rangpo caused by the Sikkim flood.

The Sikkim flood has resulted in the Rangpo area experiencing flood damage. An image captured by Praful Rao of Save the Hills organization captures the impact.

Flood damage to properties in Rangpo caused by the Sikkim flood.

The Sikkim flood resulted in property damage in Rangpo. The photo was taken by Praful Rao from Save the Hills.

There has been much talk about the possible reasons for the GLOF, which happened during a time of reported intense precipitation. Researchers have been actively investigating this matter over the weekend. Max Van Wyk de Vries from the University of Oxford shared a captivating Twitter thread, where he used satellite images to study slope activity.

There are eight comments in this discussion, therefore I highly suggest examining them closely. Essentially, Max has demonstrated that a section of moraine above the lake was unstable even prior to last week’s failure. Satellite images after the event indicate that it has indeed collapsed.

NDTV has obtained satellite images from Maxar that seem to depict a landslide.

It may come as a surprise that a landslide of this magnitude was enough to cause a breach event, but it appears to be the most likely cause.

It was widely acknowledged that this lake had the potential to cause a GLOF (glacial lake outburst flood). In fact, there have been efforts to decrease the lake’s water level using siphons in recent times. Several research papers have emphasized the dangers associated with this location, such as the one written by Sattar et al. (2021).

“Our findings indicate that the risk of GLOF (glacial lake outburst flood) will rise as the lake expands towards steep slopes, which are identified as potential areas for avalanches to occur. These avalanches have the potential to generate an impulse-wave upon impact with the lake and are the primary trigger for GLOFs in the South Lhonak Lake region.”

This appears to be surprisingly accurate. The fact that the Chungthang dam in Sikkim was at risk is not a new development – for instance, the Pulitzer Center published an article in 2014 discussing the project, which mentioned that:

The sudden arrival of glacial debris in Chungthang may damage the flush gates and the dam’s ability to release water.

After the 2021 Chamoli disaster in India, I emphasized that dam designs in the Himalayas (and other areas) often fail to properly account for the dangers posed by extreme events, particularly in a shifting climate. This incident further strengthens this argument.

Today marks the 60th anniversary of the most devastating dam disaster caused by a landslide at Vajont in Italy. It is concerning that the lessons from this event have not been heeded.

Reference

Sattar, A., Goswami, D., Kulkarni, A., Emmer, A. et al. 2021. Future Glacial Lake Outburst Flood (GLOF) hazard of the South Lhonak Lake, Sikkim Himalaya. Geomorphology,388, https://doi.org/10.1016/j.geomorph.2021.107783.

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