Another flood threat for Nepal: What is a barrier lake, and how devastating can a breach be?

Another flood threat looms for Nepal as a significant barrier lake, formed by glacial collapse, now faces a potential breach. This could unleash a devastating flood downstream, causing immense destruction. Barrier lakes, also known as landslide dams or lakes, form when debris completely blocks a river valley. They can accumulate massive volumes of water with no outlet.

If the dam breaches, it can trigger a catastrophic event called an LLOF, similar to a GLOF. The world's worst recorded LLOF occurred in 1786, killing approximately 100,000 people. Such disasters also have cross-border effects. In April 2000, a landslide in Tibet caused a flood that swept through 500 km of land, destroying bridges and displacing 50,000 people.

In 2014, Nepal experienced a similar event, where a landslide lake was emptied using geo-engineering methods. Now, with a potential breach of the barrier lake, search and rescue operations have been suspended near the Nepal-Tibet border as Chinese authorities mobilize an engineering response.