On October 3, 2023, the South Lhonak Lake, located at 5,200 meters above sea level in Sikkim, India, experienced one of the most devastating glacial lake outburst floods (GLOFs) recorded, which led to catastrophic consequences for both the local environment and human life.
A recent study published in the journal Science outlines the causes and impacts of this disaster, which began when 14.7 million cubic meters of frozen moraine debris collapsed. The collapse created a tsunami-like wave of up to 20 meters high, breaching the moraine dam and unleashing approximately 50 million cubic meters of water—enough to fill more than 20,000 Olympic-sized swimming pools.
The flood wreaked havoc along the 385-kilometer-long Teesta River valley, resulting in the deaths of at least 55 individuals and leaving 70 others missing. The disaster also severely damaged several hydropower projects, including the 1,200 megawatt Teesta-III dam, exacerbated by the intense rainfall preceding the outburst.
This incident has been attributed primarily to the destabilizing effects of climate change, particularly the thawing of permafrost, which has led to increased instability within the moraine and surrounding slopes. According to Dr. Ashim Sattar, the lead author of the study, the South Lhonak Lake has been gradually filling with meltwater due to the shrinking glaciers—a trend observed over the past several decades.
"Glacial lakes are increasingly becoming significant hazards due to our changing climate," Sattar stated. "Our findings highlight the urgent need for early warning systems and international cooperation to address such challenges."
The research team, comprised of experts from nine countries, utilized advanced technologies such as high-resolution satellite imagery and seismic data to reconstruct the precise timeline and dynamics of the flood. These tools revealed how the moraine’s gradual instability—showing displacements of up to 15 meters per year—contributed significantly to the disaster.
Christian Huggel, another co-author of the study and head of the Environment and Climate Research group at the University of Zurich, echoed the concerns about climate impacts. "This event is a stark reminder of the vulnerability of high mountain regions to the effects of climate change," he remarked.
While studies have documented the immediate impacts of this GLOF, including the erosion of around 270 million cubic meters of sediment—enough to fill 108,000 Olympic-sized swimming pools—the cascading consequences are also alarming. The flood triggered 45 secondary landslides, leading to extensive damage across borders, affecting areas not only within Sikkim but also parts of neighboring Bengal and Bangladesh.
With the reconstruction showing significant infrastructure loss, Sattar noted, "The sheer scale of this disaster emphasizes the pressing need for coordinated monitoring and proactive measures to mitigate future risks, especially along glacial lakes like South Lhonak."
The study also highlights the broader ramifications of GLOFs, indicating how climate dynamics intertwine with socio-economic factors such as hydropower development. Research has noted alarming trends where hydropower projects are being constructed closer to glacial lakes, raising the stakes for future disasters.
"There are many complex interactions between climate change, glacier mass loss, and our infrastructure," Sattar explained. "Policymakers need to adopt more ambitious regulatory frameworks to disasters like this, along with strategies for adaptive management and early warning systems aimed at protecting vulnerable communities and ecosystems."
The findings not only portray the immediate aftermath of the October 3 disaster but also serve as a wake-up call for global environmental policies concerning high-altitude regions. With rising temperatures expected to lead to more frequent and severe GLOFs, the current systems of monitoring and risk assessment have been deemed insufficient.
Moving forward, researchers call for integrating extensive climate data to develop effective risk management frameworks. They advocate for geological assessments of glacier-fed lakes and the establishment of comprehensive early warning systems capable of alerting nearby communities of impending glacier lake outburst floods.
"We have entered an era where we must urgently build resilience against these catastrophic events, not only within Sikkim but for other vulnerable high-altitude regions worldwide," Sattar concluded.
The Sikkim flood of October 2023 starkly highlights the interplay between natural hazards and climatic changes, urging immediate actions to safeguard the lives and livelihoods of communities dwelling near these potentially perilous glacial landscapes.