How warming might have caused Nepal's deadly floods

One week after catastrophic floods swept through towns along the Nepal-China border, more than 1,000 people are dead and 4,500 remain missing.

Satellite and drone images suggest that softening permafrost, or perennially frozen rock, ice and soil, on Langtang Lirung peak likely caused a massive bedrock failure and glacier collapse. An estimated 50 million metric tons of ice, rock and water—roughly 13 billion gallons, or about three times the capacity of Boulder Reservoir—fell 6,500 feet into the valley below, unleashing a slurry of mud and water that inundated bridges, hydropower facilities and villages along the way. According to the United States Geological Survey, the force of the initial debris flow hitting the ground was equivalent to a magnitude 5.2 earthquake.  

“This is by far the most horrific flood I have ever seen,” said Alton Byers, a faculty research scientist and an associate of the Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder. For the past 50 years, Byers has been studying changes in glaciers around the world, including the Himalayas, and the hazards associated with those shifts. He has lived in rural regions of Nepal for a total of eight years in addition to dozens of shorter visits since the 1970s, trekking in the mountains to study glacial lakes and help local people become more prepared for mountain hazards.

Alton Byers and Elizabeth Byers, a retired scientist with the West Virginia Department of Environmental Protection, in Nepal's Kanchenjunga region. (Courtesy of Alton Byers)

“The size of this slide totally dwarfed anything I’ve seen before. Mountains have clearly become more dangerous places to live, work and play in as Earth becomes warmer.”

As rescue teams continue searching for those still missing, CU Boulder Today spoke with Byers about what may have triggered the disaster, how climate change is reshaping glaciers and mountain hazards around the world, and whether similar events could occur in the United States.

Has melting permafrost led to similar disasters before?

Since the 1850s, changes in high-altitude permafrost have contributed to dozens of these cascading disasters in Nepal and parts of India, in which bedrock and glaciers break off, and trigger massive flash floods and debris flows. For example, in 2012 a slurry flood in central Nepal, similar to what happened in Nepal last week, killed 79 people along the Seti River. In 1970, an earthquake triggered the collapse of a glacier in Peru, creating a massive debris flow that buried more than 20,000 people in minutes in the village of Yungay.

Did climate change play a role in what happened in Nepal last week?

Warming trends certainly played a major role, destabilizing and softening permafrost, often referred to as the “cryospheric glue,” since the 1860s. Permafrost has been holding the mountains together for millennia. But as it melts, masses of rock and glacier are no longer as resistant to gravity as they once were. So the likelihood of breakage is greater.

Are unstable glaciers and permafrost a risk in the United States?

In Colorado, we’ve been losing glaciers for a long time due to warming, so they are generally small and not as dangerous in terms of permafrost-related slope failures. But mountains are just in general less stable now compared to how they used to be.

In places like Alaska, people have expressed concerns about the increase in landslides related to changes in permafrost. Last year, a landslide in Alaska’s Tracy Arm Fjord triggered a massive tsunami with a wave rising some 1,580 feet above sea level.

What other glacier-related hazards are scientists watching?

Scientists have been studying glacial lake outburst floods for decades. 

Glacial lakes form when glaciers recede and water fills the area left behind. An avalanche, landslide or flood from an upstream lake can trigger a surge wave that breaches the unstable lake barrier, unleashing a huge amount of water and causing catastrophic downstream flooding.

Could last week’s disaster have been predicted? 

Not really. You can’t predict things of that nature. It’s also hard to predict a glacial lake outburst flood. But what we can do is identify areas of high risk ahead of time, such as overhanging ice on a mountain slope with an urban area downstream. We need to monitor them regularly for any obvious changes. 

What can we do to reduce the damage from future, similar events?

Besides monitoring, I think we need to discourage this trend of the last 20 years of building in floodplains, because hazards are bound to happen. There are dozens of similar urban areas along other rivers throughout the Himalayas that have glacial landscapes upstream. All of them need an effective and accessible early warning system and evacuation plans.

We live in a changing world and a changing mountain world. So we’ll need to continue to find ways to adapt.