Barrier lake forms after Gyirong mudslide in Xizang

A powerful mudslide struck Gyirong County in southwest China’s Xizang Autonomous Region on Thursday, 26 August 2023. The slide was large enough to block a river that flows across the border, creating a dangerous new lake behind the debris. The event added serious secondary risks to the rescue work that was already underway. The story shows how one natural disaster can trigger another, and why careful monitoring is essential.

The mudslide was caused by a sudden collapse of loose soil and rock on a steep slope. When the material fell, it rushed downhill and hit the river channel. The debris piled up in the waterway, forming a natural barrier that stopped the flow of the river. This blockage is what created the new lake behind the debris.

A barrier lake is a temporary body of water that forms when a river is blocked by loose material such as rock, soil, ice, or debris from a landslide or avalanche. The material acts like a dam, but it is not made of concrete. Because the dam is made of loose, shifting material, it can give way if the water overtops it or if the material slides. When that happens, the lake can suddenly burst and flood the land downstream.

Rescue teams first measured the size of the barrier. They found it was about 150 meters long and 40 to 50 meters high. The lake behind the barrier could hold between 1.5 and 2 million cubic meters of water. On the day the slide happened, the lake already held about 2 million cubic meters and was already spilling over the top of the barrier. Experts say that another 3 million cubic meters of water could enter the lake in the next three days.