As Nepal reels from deadly flash floods, scientists say the flooding was triggered by the collapse of a glacier.
University of Michigan geoscientist Marin Clark studies how erosion processes at the land surface, like landslides and river floods, cause disasters, and she has specifically studied landslide hazards in Nepal. Clark is currently the lead principal investigator and director of the Center for Land Surface Hazards or CLaSH, a research group funded by the U.S. National Science Foundation to advance the scientific understanding of natural hazards and how they can cascade, amplifying their effects on people and the landscapes in which they live.
Clark, a professor in the Department of Earth and Environmental Sciences, can speak to the events that triggered the Nepal disaster, and what might come next for the country.
Can you describe what led to such catastrophic floods in Nepal?
We're still not sure of all the details, but we have seen evidence of a glacier collapse way up in the river headwaters. We see this on satellite images, and there was a seismic event recorded that has been attributed to the collapse of a piece of the glacier. But how exactly that collapse is related to the initiation of a flood is still under a lot of speculation. Meltwater from the glacier and icy sediment could have contributed, or there may have been some temporary blockages of the river that dammed and later released a lot of water at once.
But the collapse did initiate this debris flood-debris floods occur when a lot of water, sediment and rocks are mixed together. These debris floods have a lot of momentum and can travel a really long way downstream, picking up more rock and sediment as it travels. This flood had a really astonishing reach.
The CLaSH team has created an ArcStoryMap to compile resources, showcase initial findings and analysis and share information about the Nepal events with the community.
What are cascading natural hazards?
Cascading natural hazards refer to when a single event sets off a chain reaction of other disastrous events that increase threat levels for communities for weeks to years in the future. So we know that the hazard in Nepal won't be over once the flood recedes. There seems to be this new lake forming up in the area where the first glacial collapse happened. It's ponding water, and if that water catastrophically gets released downstream, that can create a second flood. That new lake, and the potential new flood, is related to the first event. That's part of the domino effect of cascading hazards.
Another thing we know is that sediment that has traveled down the river has rearranged the river and its shape, so its ability to hold water has changed. That will, in subsequent monsoon seasons, lead to new flooding hazards along the complete path of the runout of this particular flood.
For example, if you could imagine filling your bathtub with sediment and sand, and then put your normal amount of bathwater in it, it would spill out all over the floor. That's what's going to happen in the future in some of the reaches affected by this particular flood, creating an ongoing risk to the communities affected by this event.
Are events like this increasing in frequency, and if so, what role does global change play in the frequency of natural disasters?
These do seem to be increasing in frequency, and climate plays a role in a couple different ways. Warmer temperatures can cause glacial collapse or ice avalanches, like the kind we may have seen today. They've been a big problem in Alaska, where pieces of glacier have collapsed and created tsunamis along coastal regions. In the Himalaya, we're also seeing potential intensification of storms, and rain-on-snow events, both of which can create flash flooding.
Why is it important to study the connections between natural hazards?
We need better ways of seeing the long game. Understanding how one hazard connects to another gives us better predictive tools to make more resilient societies. The mission of CLaSH is to try to understand the science that connects those hazards together.
The first trigger of a hazard is often unpredictable, or known with very little warning, like the glacial collapse that happened this week. But now that it's happened, being able to understand what happens next and where the biggest areas of risk are, in the following months to years, we can have better mitigation strategies to protect communities.
Can you describe your current research in Nepal?
I've been working in Nepal since 2015, following the Gorkha earthquake, a magnitude 7.8 earthquake, and in the Himalaya and Tibet system my whole career. The Gorkha earthquake was particularly significant because the period of strong ground shaking triggered nearly 25,000 landslides across central Nepal. My work began with studying that earthquake-triggered landsliding event, and then progressed to later studies in the past five or six years where we've been looking at the interaction of mountain hazards and mountain hydrology.
We've been looking at the Himalaya as a case study of a system where both hazards and water resources are tightly coupled, and I've been trying to understand how those systems work. I've been working directly in the area that was affected this week for the past decade, on various studies with Nepali collaborators as well as a team of U.S. and U.K. collaborators.
