Seismic Shocks Raise Alarm for Glacial Lakes in Bhutan: Preparedness is Key

The recent 7.1 magnitude earthquake that shook the Shingtse region of Tibet on January 7 has raised significant concerns regarding the stability of glacial lakes in Lunana, Bhutan. The tremors, which were felt across the border, particularly impacted Gasa, the dzongkhag closest to the earthquake’s epicenter, where residents experienced a maximum intensity of four on the Modified Mercalli Intensity (MMI) scale. In the wake of the earthquake, two avalanches were triggered from the Table Mountain above the Bechung Glacier. Fortunately, the gentle slope of the glacier managed to absorb the avalanches, preventing them from cascading down to the Bechung Glacial Lake. However, experts caution that such seismic events pose risks for Glacial Lake Outburst Floods (GLOFs), which can have devastating consequences for communities downstream. Lunana, known for its numerous glaciers, is particularly vulnerable due to its unique topography. Glacial lakes, including Bechung, Rapstreng, Thorthomi, and Lugye Tsho, are all located below the Table Mountain and could be at risk following seismic events. Phuntsho Tshering, the executive glaciologist at the National Centre for Hydrology and Meteorology (NCHM), highlighted the potential dangers, stating, "The vibrations destabilise glaciers, triggering avalanches. Fortunately, this avalanche occurred on the Bechung Glacier side, which has a slope capable of absorbing the impact." Despite the initial concerns, assessments conducted by NCHM staff in Lunana revealed no major disturbances at the Thorthomi, Rapstreng, and Bechung lakes. Minor moraine slides were observed at the Thorthomi-Rapstreng barrier, a critical structure that has been deteriorating over the years. With the potential for a catastrophic outflow of 53 million cubic meters of water should the moraine dam collapse, Thorthomi Lake remains the most dangerous glacial lake in the region. In response to these risks, the NCHM has been proactive in relocating communities residing near Thorthomi Lake to safer elevations. Efforts to move residents from Thangza and Tenchoe villages to higher ground at Damthangkha, Bayza-Gangjuk, and Dungbiteng have been ongoing since last year. The earthquake's tremors were notably milder in other parts of Bhutan, with intensities ranging from zero to three, particularly in western regions where the intensity was recorded at two. Bhutan's existing building codes are designed to withstand ground shaking of up to 0.36g, providing a degree of structural safety amid seismic threats. Looking ahead, the Department of Geology and Mines is collaborating with the GovTech Agency to enhance Bhutan's earthquake monitoring systems. This upgrade, expected to be completed by the end of March, will introduce a web-based platform for real-time earthquake intensity information, empowering citizens to report perceived shaking and further bolster disaster readiness. As the NCHM continues to monitor the glacial lakes, they urge communities downstream to remain vigilant. The interconnectedness between climate change, glacial movements, and seismic activity underscores the need for ongoing vigilance and preparedness in areas like Lunana, where the impacts of natural disasters can be profound and far-reaching.