What’s the news?

• On October 4th, in a tragic turn of events, Sikkim witnessed a devastating incident where the South Lhonak Lake ruptured due to incessant rainfall, resulting in the loss of fourteen lives and the disappearance of 102 individuals, including 23 Army personnel.

Central idea

• Sikkim, nestled in the Himalayas, faces the aftermath of a catastrophic Glacial Lake Outburst Flood (GLOF) triggered by incessant rainfall. The South Lhonak Lake, perched at 17,000 feet in the state’s northwest, burst, inundating four districts—Mangan, Gangtok, Pakyong, and Namchi.

What are glacial lakes?

• Glacial lakes are large bodies of water that are typically located in proximity to, on top of, or beneath glaciers.
• These lakes are primarily formed as a result of glacial processes, such as the melting of ice and the accumulation of meltwater in depressions or basins created by the glacier’s movement.

Concept: Glacial Lake Outburst Floods (GLOF)

• A Glacial Lake Outburst Flood (GLOF) is a sudden and often catastrophic release of water from a glacial lake, typically caused by the breach or failure of the natural dams that contain the lake.
• GLOFs occur in regions with glaciers, where meltwater accumulates in depressions or basins created by the glacier’s movement.
• These floods can have severe and far-reaching consequences for downstream communities and environments.

Causes: GLOFs can be triggered by various factors

• Melting Glaciers: Rapid glacier melt due to rising temperatures can increase the volume of water in glacial lakes.
• Avalanches: Snow or ice avalanches can impact the lake, dislodging ice and debris into the water.
• Earthquakes: Seismic activity can destabilize the natural dams or trigger avalanches.
• Rainfall: Heavy rainfall can contribute additional water to the lake and weaken natural dams.
• Volcanic Eruptions: Volcanic activity can lead to the rapid melting of glaciers and the formation of glacial lakes.

Destruction and Impact

• Flooding: Downstream areas can experience rapid and extensive flooding, with water levels rising quickly.
• Destruction of Infrastructure: GLOFs can damage or destroy roads, bridges, buildings, and farmland.
• Loss of Life: GLOFs often result in the loss of human lives as well as harm to livestock and wildlife.
• Environmental Damage: The floodwaters and debris can severely impact the natural environment, including forests, wetlands, and river ecosystems.

Notable GLOF events

• Some GLOF events in the past have resulted in significant loss of life and damage to infrastructure.
• The horrifying 2013 flash floods in Uttarakhand’s Kedarnath serve as a stark reminder of the devastating consequences of GLOFs.
• This calamity was compounded by a GLOF event originating from the Chorabari Tal glacial lake, leading to the loss of thousands of lives.

The Sikkim Calamity: South Lhonak Lake’s Susceptibility to GLOF

• Glacial Melting: Rising global temperatures have accelerated the melting of glaciers in the Sikkim Himalayas, including the glacier feeding South Lhonak Lake. This increased meltwater contributes to the lake’s water volume, making it more susceptible to GLOFs.
• Glacial Lake Expansion: The South Lhonak Lake’s area has significantly increased over the past five decades. It has grown nearly 1.5 times, while its neighbor, North Lhonak, has expanded nearly 2.5 times its initial size in 1989. This expansion is a direct result of glacier retreat and melt, exacerbating the lake’s vulnerability.
• Seismic Activity: The region around South Lhonak Lake is prone to seismic activity. Earthquakes can destabilize the natural dams or trigger avalanches, which can lead to a sudden release of water from the lake, potentially causing a GLOF event.
• Past Earthquakes: Seismic events occurred in the region, such as an earthquake of magnitude 4.9 in 1991 near the parent glacier feeding South Lhonak Lake and another earthquake of magnitude 6.9 in 2011, approximately 70 km from the lakes. These past earthquakes and the potential for future seismic activity increase the risk of GLOFs in the area.

Government interventions

• Syphoning Off Lake Water: In 2016, the Sikkim government, in collaboration with various agencies including the Sikkim State Disaster Management Authority and Sikkim’s Department of Science and Technology and Climate Change, took proactive measures to mitigate the risk associated with South Lhonak Lake. They decided to syphon off water from the lake.
• Innovative Approach: The technique employed for syphoning off lake water was innovative and effective. Under the supervision of innovator Sonam Wangchuk, authorities installed three eight-inch-wide and 130-140-meter-long High-Density Polyethylene (HDPE) pipes in the lake. These pipes were used to extract water from the lake.
• Water Extraction Rate: The initiative successfully extracted 150 liters of water per second from South Lhonak Lake, which was a substantial volume. This action aimed to reduce the water level in the lake, thus mitigating the risk of a potential GLOF.

Way forward: Warning and Mitigation

• Lake Monitoring: Regular monitoring of glacial lakes to assess changes in water levels and the stability of natural dams
• Early Warning Systems: Implementing systems to detect and warn downstream communities of potential GLOFs
• Infrastructure: constructing protective infrastructure, such as dams or diversion channels, to manage floodwaters
• Land-Use Planning: Implementing land-use planning and zoning to restrict construction in high-risk areas

Conclusion

• The recent calamity in Sikkim underscores the imminent threat of GLOFs in the Himalayan region. While government initiatives are commendable, continued monitoring, research, and disaster preparedness are vital to safeguarding vulnerable communities in the face of the expanding glacial lakes and the looming specter of GLOFs.

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