Delayed Flood Alerts

The Rasuwa-Bhotekoshi flood has killed more than 1,450 people, left more than 5,000 people missing, and affected nearly 33,000 residents. According to the NDRRMA Rapid Assessment Report, the disaster caused an estimated $2.695 billion in total financial effects with approximately $4.775 billion in recovery needs. We are still learning what happened above Langtang Lirung. Evidence so far points to a huge slab of glacier and bedrock, breaking off the peak's north face and falling into the valley, hitting the ground hard enough to generate a seismic signal comparable to a magnitude-5.2 earthquake. It dammed the Lhende Khola; when that debris dam gave way, it sent the flood racing down the Trishuli. 

While researchers continue to investigate the precise sequence of events, the emerging evidence points to the mountain collapse itself generating the seismic signal rather than being triggered by a tectonic earthquake. One thread runs through many expert accounts: permafrost, the frozen ground that can help stabilize mountain slopes, is thawing. Alton Byers, a glacier hazards researcher, has compared the effect to butter taken out of the fridge and left on the counter: it softens, and eventually loses its structural integrity. That is not the same as saying permafrost thaw alone caused this disaster. But researchers argue it is likely one reason the mountain was primed to fail.

That is the uncomfortable part for Nepal. Our disaster monitoring has focused heavily on hazards we can see: glacial lakes swelling behind moraine dams. What we cannot easily see is what is happening deep inside mountains. Scientists argue that decades of warming have pushed the freezing line, the elevation above which temperatures stay below zero, upward.