On the morning of August 26, 2026, part of a mountain—including permafrost, rocks, and a portion of a glacier—collapsed on the Tibet-Nepal border, unleashing a wall of ice, water, rock, sediment, and debris that tore through mountain villages and swept away roads, bridges, and 12 hydropower plants.
More than 1,300 people are dead and thousands more remain missing. Along with the human tragedy, the flood knocked out more than 10% of Nepal's electricity generation capacity, exposing the fragility of a country that generates nearly all of its own electricity from hydropower.
Nepal's success in building clean energy infrastructure is now jeopardized by a warming world and the glacial instability it brings. Dartmouth Engineering Research Scientist Aleah Sommers has spent years studying glaciers and meltwater in the Himalayas and polar regions. Her work, alongside other scientific research and monitoring, helps explain what just happened in Nepal.
It can also inform investment decisions as Nepal rebuilds, as well as in other regions worldwide facing similar risks from glacial melt.
Sommers' research focuses on the hidden processes happening beneath the ice. "I study interactions between glaciers and water, especially water that makes its way to the bottom of the ice and influences how fast the glacier moves by sliding over the rocks or sediment below," said Sommers. "This environment is extremely difficult to observe directly, either in the field or from remote sensing, but we can use mathematical models that calculate the flow of ice and water and how they interact to gain insights into processes and responses playing out under the ice."
That approach has produced findings with direct relevance to the Nepal disaster. "In my research on Himalayan glaciers, we have documented through modeling and remote sensing that some Himalayan glaciers are sensitive to changes in meltwater reaching their beds. Under the right conditions, even a very tiny amount of meltwater draining through to the bedrock can trigger a dramatic and rapid acceleration of the ice."
Sommers' research offers a scientific lens for understanding the mechanics behind the August 26 collapse. Preliminary investigations point to failure of recently exposed permafrost rocks underlying part of a glacier as the cause of the flash flood. Water draining below the glacier may have played a key role, consistent with the patterns Sommers has documented elsewhere. The Himalayas are warming roughly 50% faster than the global average, destabilizing ice and rock formations that have held steady for generations.
A glacier in the Himalayas, with a lake of meltwater at the base. | Photo by Aleah Sommers
Mathieu Morlighem, the Evans Family Professor of Earth Sciences at Dartmouth, studies ice dynamics using numerical models and has been working with Sommers for several years.
"Our computer models have become very good at telling us how large ice masses respond to a warming atmosphere over years to decades," he said. "What they are not yet built to do is tell us which slope will fail next week. Events like this one fall into the gap between long-term projection and short-term warning, and closing it will take far better observations of these steep, remote, barely instrumented environments."
"From our work, we know that glaciers are sensitive to water beneath them," said Sommers. "Conditions in these mountains can be extreme and unpredictable at the best of times. Himalayan mountains are incredibly steep and crumbly, glaciers are retreating, their lakes are expanding, and hazards such as outburst floods, landslides, and avalanches are common.”
She reflected on her time living in India, where she “...personally experienced many road blockages and closures from landslides during the monsoon season, which are just a fact of life for people in the Himalayas. In the recent Nepal-Tibet disaster, a bunch of processes combined in the worst kind of abrupt way, in a high altitude remote location, with enormous downstream impact. We still have a lot to do in terms of understanding the complex physical processes at play, as well as figuring out how better to monitor, predict, and respond to such events."
For Sommers, who last year taught at a workshop in Kathmandu, Nepal, focused on "Remote Sensing for Monitoring and Modelling of Hazards in High Mountain Asia," knows people from the affected area in Nepal with many family members missing. "It's heartwrenching to imagine what it must be like."
Sudarshan Regmi, a second-year PhD student in computer science whose family lives in Kathmandu—roughly 35 miles from areas affected by the floods—said the disaster "affected me deeply and mentally." Watching the crisis unfold from afar has been difficult, he added: "The footage circulating on social media is frightening."
For Regmi, the floods also underscore a broader inequity he feels strongly about: "Nepal is not a major contributor to global climate change, yet we are among those most affected by its impacts."
Sommers is working to improve understanding of the role of subglacial hydrology in glacier surges and outburst floods through numerical modeling, in a project funded by NASA and involving international collaborators based in High Mountain Asia. Through a Faculty Seed Grant from the Irving Institute, she along with Colin Meyer and Mashrekur Rahman, also aims to use machine learning techniques and data-driven tools—drawing on model results, field observations, and remote sensing—to predict meltwater dynamics and inform water security under climate change.
In June, she led a group of Dartmouth researchers to teach at and participate in an intensive glaciology summer school course in Ladakh, along with glacier fieldwork with Indian collaborators and Morlighem. Sommers' collaborations with Indian institutions are ongoing and expanding, bringing together modeling, field observations, and remote sensing expertise.
A research site in the Himalayas overlooking the Drang Drung Glacier and its lake in Ladakh, India. | Photo by Aleah Sommers
The Nepal disaster is a stark illustration of a broader vulnerability: what happens when a nation's energy system depends almost entirely on a single, climate-exposed resource. Geoff Parker, faculty director at the Irving Institute, supports research investigating how energy systems can be designed to withstand a range of disruptions.
"When a single energy source generates nearly all of a country's electricity, that country is exposed to any disruption to that source, whether it's a climate-driven disaster, a geopolitical conflict, or a technical failure," said Parker. "Energy diversification is good climate policy and good risk management."
Nepal's experience underscores the stakes of overdependence on a single source. "Nearly all of Nepal's domestic electricity generation comes from hydropower, and a single event wiped out about 10 percent of that capacity overnight," Parker said. "That is the risk of concentrating so much of a national energy system in one resource. Diversifying across sources, such as solar, wind, and hydro, would spread that risk so that a single failure cannot take down a significant portion of the system.”
Parker points to Uruguay as a useful comparison. "Uruguay has long been hydro-dependent, and hydro is still its largest single source, at around 45 percent," Parker said. "In 2023, drought cut that output by roughly two-thirds. But over the previous decade Uruguay added wind and biomass to displace the fossil fuel it used to import, it also kept fossil fuel as “firm” backup on the system and had the transmission to buy electricity from Brazil when needed. The result was an expensive year, not a national emergency."
Parker notes that "Nepal already lives with this problem every winter. Run-of-river output falls by approximately 40-50%. Nepal buys several hundred megawatts from India to cover the gap. Solar can cover the gap in those dry months and it can be built hundreds of kilometers from the nearest glacier to protect from catastrophic melt."
For Parker, the path forward depends on research like what Sommers is undertaking. "It helps us understand why these disasters happen, and gives us the tools to make more informed decisions about where and how we build," he said. "If we know which regions face elevated risk from glacial instability, we can factor that directly into where new infrastructure is sited, how to design for resilience, and how to prioritize early-warning systems. That's how fundamental science informs practical policy and resource allocation."
“Detection and warning are two different problems, and we tend to solve only the first one. A satellite can flag an expanding glacial lake, but that signal has to become a message someone trusts, understands, and acts on within minutes, often in a language, a literacy context, and a level of institutional trust that the alert was never designed for. The science of the last mile is behavioral, and right now it is the least funded part of the chain," according to Kimberly Rose Clark, leader of Dartmouth’s Initiative for Research on Energy Communication Transformation Lab.
Sommers' research sits at the intersection of understanding this problem and helping to solve it, and may become even more relevant in the years to come.
"As the Himalayas and polar regions continue to warm, glacier-related hazards will continue to occur and evolve," said Sommers. "The drivers involved are complex, and catastrophic events are challenging to predict. This event highlights the human cost of gaps in both knowledge and preparedness, and points toward a need for significant investment into scientific research, monitoring, and early-warning infrastructure."
Research program coordinator Andrila Hait Chakrabarti contributed to this report.