Shigatse quake shows danger of GLOF induced by quakes after avalanches and moraine slides

The 7.1 magnitude earthquake that struck the Shigatse region of Tibet, China, on 7th January 2025 caused two avalanches from the Table Mountain above Bechung Glacier in Lunana. While the glacier’s gentle slope absorbed the avalanches and prevented them from reaching the Bechung Glacial Lake, such events highlight the potential risk of Glacial Lake Outburst Floods (GLOFs) in the region.

The tremors of the Shigatse earthquake were felt across neighboring countries, including Bhutan, with Gasa experiencing the maximum intensity of four on the Modified Mercalli Intensity (MMI) scale.

Followed by the most felt intensity in western Bhutan was 2 on the MMI.

MMI estimates the shaking intensity from an earthquake at a specific location by considering its effects on people, objects, and buildings. At high intensities (above MMI 6), earthquake shaking damages buildings

The National Centre for Hydrology and Meteorology (NCHM) reported that Lunana’s glacial lakes are particularly at risk due to their glacial topography. Seismic activity, such as earthquakes, destabilizes glaciers and can trigger avalanches.

Phuntsho Tshering, Principal Hydromet Officer at NCHM, said, “Vibrations can destabilize glaciers and lead to avalanches. Thankfully, this particular avalanche took place on the Bechung Glacier side, where the slope is capable of absorbing the impact.”

He said that if an avalanche of such magnitude had fallen into the critically dangerous Thorthormi or Rapstreng Lakes, located just below the base of Table Mountain, it could have generated a massive wave. If this wave had struck the end moraine, it might have led to a dam failure. Fortunately, this was not the case this time.

A potential collapse could release 53 million cubic meters of water, resulting in catastrophic downstream flooding.

NCHM has emphasized the need for continuous monitoring and early warning systems to mitigate such risks.

A field team from the NCHM stationed in Lunana was deployed to assess the glacial lakes. Their observations included Thorthomi, Rapstreng, and Bechung Lakes, where no major disturbances were observed. However, minor moraine slides were noted on the inner moraine walls of the Thorthomi-Rapstreng barrier.

The Chief of Cryosphere, Karma, said, “Based on our assessment, there are no cracks on the moraine walls, except for a few minor slides.”

Further, Director of the Department of Geology and Mines (DGM), Phuntsho Namgyal, explained that the structural integrity of natural materials, like earth or rock, is generally not a significant concern in the presence of small cracks.

“Unlike artificial materials, such as cement or steel, which require careful maintenance when cracks are present, natural materials have a different dynamic. Small cracks in earth or rock are usually stable, and minor issues can naturally stabilize through processes like thawing and freezing,” he said.

The Director emphasized that if major cracks existed in the area, they would be visible to the naked eye. He also recommended that in seismically active zones, it is preferable to use natural materials, such as earth-filled structures, over artificial materials for building dams and barriers.

“Above there, it is all natural materials,” he said.

As for Luggye Lake, it is inaccessible due to winter conditions.

Currently, a team from NCHM is stationed in Lunana. The team is a part of Lunana Thangza Group actively working on-site. The team will be conducting continuous monitoring in coordination with the NCHM headquarters. They also plan to carry out field visits to the lake sites in the coming days to ensure comprehensive surveillance and data collection. 

Meanwhile, the public residing downstream has been advised to remain vigilant during this period. Residents of Thangza and Toenchoe were recommended to relocate as a precautionary measure last year. However, the people in these two chiwogs are still awaiting financial aid to begin rebuilding their lives properly at the new location.

Likewise, DGM, in collaboration with the GovTech Agency, is upgrading the country’s earthquake monitoring systems. Scheduled for completion by March 2025, the upgrades include a web-based service providing a platform for real-time earthquake intensity information, and accessible to the public, which will also allow users to report their experiences of perceived shaking.

Color-based intensity Distribution Maps, an auto-generated maps depicting instrumental and observed intensity distributions. Automated Dissemination: Earthquake source information will be automatically sent to relevant stakeholders via SMS and email.

Earthquake Bulletin is an automated generation of earthquake bulletins for dissemination to stakeholders and the media.

Currently, Bhutan operates 13 seismic monitoring stations and 223 intensity meters across the country. Events are auto-detected, verified, and disseminated manually to relevant stakeholders, ensuring timely updates.

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