The research, titled ‘Alarming trends: rapidly growing and recently formed glacial lakes in the Alaknanda Basin, northern Indian Himalayas,’ was conducted by Dr Aayushi Pandey of Charles University in Prague, Czech Republic. It focused on the Alaknanda Basin, a heavily glaciated catchment in the western Himalayas of India whose waters ultimately feed some of the most densely populated river systems on Earth. Using space-based observations from the Landsat and Sentinel-2 satellite missions, the study mapped changes in 74 glacial lakes across the basin between 1994 and 2023, producing one of the most detailed long-term pictures yet of how this high-altitude landscape is being reshaped by a warming climate.

The numbers reveal how quickly the transformation is unfolding. The combined area of 24 glacial lakes larger than 0.01 square kilometres – a low cut-off threshold used in the methodology to exclude small seasonal water bodies – grew from 0.97 square kilometres in 1994 to 1.62 square kilometres in 2023. That represents an increase of 67 percent in just 30 years, a remarkable rate of change for landscape features that were once considered permanent fixtures of the high mountains. Each additional hectare of lake surface represents water pooled behind natural barriers of ice, rock or sediment, sometimes in precarious positions on steep slopes.

Equally significant is the discovery that the phenomenon is not limited to existing lakes simply getting bigger. The study identified 57 new glacial lakes that formed during the three-decade study period, bringing the total number of lakes in the basin to 131. Of these newly formed water bodies, 18 exceeded the 0.01 square kilometre threshold, meaning they are large enough to pose meaningful hazards if they were to fail. The emergence of so many new lakes in a single basin illustrates how rapidly retreating glaciers are leaving behind depressions that fill with meltwater, effectively creating new reservoirs in some of the most inaccessible terrain on the planet.

Some individual lakes have grown at rates that demand particular attention. Vasundhara Lake expanded by 261 percent between 1994 and 2023, nearly quadrupling in surface area over the study period, while Balbala Lake grew by 119 percent. The research also flagged 27 glacial lakes showing notable growth, including one situated upstream of Badrinath, one of the most important pilgrimage sites in the Indian Himalayas, which draws enormous seasonal crowds of visitors. The author singles out the very rapid expansion of Vasundhara Lake as requiring close attention, noting that these lakes warrant continued monitoring and further assessment because changes in their size and stability could have serious consequences for communities and infrastructure downstream.

The hazard in question is known as a Glacial Lake Outburst Flood, or GLOF. These events occur when water held back by ice, rock or sediment is suddenly released, sending a torrent of water, mud and debris down narrow mountain valleys with potentially devastating force. Because glacial lakes often sit at high elevations above villages, roads, bridges and hydropower installations, even a modest volume of released water can gain destructive momentum as it descends. The mechanisms of failure can include avalanches of ice or rock plunging into a lake, the collapse of moraine dams, or the sudden drainage of ice-dammed water bodies, and in many cases there is little or no warning for people living downstream.

While the recent disaster in Nepal was not itself a conventional GLOF, it demonstrates the extraordinary consequences that sudden high-mountain flood events can inflict on communities and infrastructure. Nepal’s government reports that the August floods caused widespread damage to houses, roads, bridges and hydropower facilities, and recovery efforts are still ongoing. The episode serves as a stark illustration of how vulnerable Himalayan societies remain to water-related hazards originating in remote high-altitude terrain, and why scientists argue that understanding the evolving glacial lake landscape is a matter of urgent practical importance rather than purely academic interest.

‘The recent flooding is a reminder of how important it is to continuously monitor high-mountain environments where multiple hazards including extreme rainfall, glacial lake expansion, slope instability and seismic activity can interact and potentially amplify downstream impacts,’ says study author Dr Aayushi Pandey. Her point underscores a growing recognition among hazard researchers that mountain disasters rarely stem from a single cause. Instead, compound and cascading hazards – a heavy rainfall event striking a slope already destabilised by melting permafrost, for example, or an avalanche dumping into an expanded glacial lake – can multiply the risks faced by downstream populations in ways that individual hazard assessments may miss.

Satellite data, Pandey notes, are extremely valuable for screening such a large and inaccessible region. ‘They allow us to identify newly formed lakes, measure changes in lake area, identify rapidly expanding lakes and shortlist those that need detailed investigation,’ she says. ‘But that’s not the complete solution. Field measurements are essential to determine lake depth and volume, assess slope stability, understand drainage pathways and glacier–lake interactions, and improve flood modelling.’ In other words, remote sensing can tell researchers where to look, but only ground-based work can reveal how much water a lake actually holds, how stable its dam is, and what would happen if it failed – the information needed to build reliable early warning systems and flood models.

That fieldwork, however, comes at a cost. Pandey emphasises that it requires substantial logistical and financial support, including stronger transboundary scientific cooperation and data sharing, because glacial-lake and flood hazards do not follow political boundaries and should be addressed as a shared regional concern. The Himalayas span multiple countries, and rivers fed by these mountains sustain hundreds of millions of people across South Asia. As the new study of the Alaknanda Basin makes clear, the pace of change on the ground – and on the ice – is outstripping the pace of monitoring. Whether the region’s growing inventory of glacial lakes becomes a catalogue of near misses or a series of future disasters may depend on how quickly that gap is closed.

Subject of Research: Satellite-based monitoring of newly formed and rapidly expanding glacial lakes in the Alaknanda Basin of the northern Indian Himalayas and their associated outburst flood risk.

Article Title: Himalayan glacial lakes are growing – and so is the downstream flood risk

Article References: Himalayan glacial lakes are growing – and so is the downstream flood risk. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: glacial lakes, Himalayas, glacial lake outburst floods, climate change, Alaknanda Basin, satellite monitoring, Landsat, Sentinel-2, glacier retreat, flood risk, Open Geosciences, northern India

On October 3, a staggering volume of 14.7 million cubic meters of frozen moraine material careened into the South Lhonak Lake, creating an immediate and devastating tsunami-like wave that reached heights of 20 meters. This initial event, characterized by the release of tremendous kinetic energy, set off a chain reaction, culminating in a glacial lake outburst flood that unleashed around 50 million cubic meters of water. Cementing this tragedy’s magnitude, this volume of water could fill an estimated 20,000 Olympic-sized swimming pools and wreaked havoc across a 385-kilometer stretch of the valley.

The aftermath of this disaster was nothing short of dire; infrastructure such as hydroelectric power plants along the Teesta River faced annihilation as torrents of water cascaded down the valley. Additionally, an estimated 270 million cubic meters of sediment were dislodged and washed away, affecting the ecology and geomorphology of the region. Tragically, this natural disaster also claimed the lives of at least 55 individuals, while an additional 70 remain unaccounted for, underlining the humanitarian toll accompanying such environmental calamities.

The co-author of the study, Christian Huggel, emphasized the urgency of recognizing the high vulnerability of mountain regions amidst the threat of climate change. Melting permafrost and the destabilization of geologic materials, such as rock and ice, create precarious conditions that invite disaster. Huggel’s insights provide a clarion call to the scientific community and policymakers alike to adopt more proactive stances when it comes to addressing the threats posed by a warming world.

To understand the intricacies of this disaster, researchers employed a suite of advanced scientific methodologies. High-resolution satellite imagery, combined with digital elevation models and sophisticated numerical simulations, enabled a granular reconstruction of the flood’s dynamics and effects. Furthermore, integrating seismic data provided crucial temporal markers for events such as the moraine collapse. Geomorphological analyses quantified the volumes of both water and sediment released, painting a comprehensive picture of the multifaceted disaster.

High-resolution remote sensing technologies proved indispensable in dissecting the cascading effects and complex processes at play during the flood. First author Ashim Sattar, who transitioned from postdoctoral research at UZH to an academic position at the Indian Institute of Technology in Bhubaneswar, noted that interdisciplinary collaboration was fundamental to uncovering the full scope of this crisis. The feasibility of such scientific partnerships highlights the importance of collaborative approaches when confronting global issues.

In the wake of this disaster, the analysis conducted by the research team raised alarm bells regarding the need for effective early warning systems and collaborative strategies that transcend national borders. The destruction of essential infrastructure, including five hydroelectric power plants, and the severe erosion and sedimentation caused by the flood impose grave consequences on local farmers, business owners, and the regional economy. In this context, Sattar’s findings suggest a roadmap for mitigating future disasters through enhanced international cooperation and preparedness.

The researchers also underscored that signs of instability within the moraine were recorded well in advance of the disaster, a fact that could have informed more efficacious monitoring and response strategies. Historically unprecedented shifts of up to 15 meters per year in the moraines pointed to underlying vulnerabilities that went largely unaddressed. This emphasizes the necessity of coordinated surveillance and proactive measures tailored to high-risk mountain regions where little margin for error exists.

Addressing the looming threats posed by climate change necessitates better risk modeling, assessment, and robust strategies for adaptation. The influx of warming temperatures increases the likelihood that glacial lake outburst floods will become more frequent and severe. The incident surrounding South Lhonak Lake highlights the dire need for raising awareness and taking actionable measures to tackle climate risks, especially in vulnerable mountainous regions globally.

Furthermore, the researchers advocate for stricter regulations governing hydropower development in precarious areas and heightened oversight of glacial lakes—factors that are only becoming more pressing as climate conditions continue to shift. By integrating early warning systems into these regions’ strategic planning, communities can develop resilience against the mounting threats posed by climate change.

In summary, the Sikkim flood of October 2023 encapsulates a crucial moment in understanding the interplay between climate change and natural disasters in high-altitude environments. The insights unearthed by this international research initiative serve as a poignant reminder of the urgency with which we must confront climate-related challenges. Preparing communities to navigate the growing complexities of climate-induced disasters will not only enhance their resilience but will also illuminate pathways toward more sustainable living in an ever-changing world.

Subject of Research: Flood disaster analysis
Article Title: The Sikkim flood of October 2023: Drivers, causes and impacts of a multihazard cascade
News Publication Date: 30-Jan-2025
Web References: [Link to Research Article]
References: A. Sattar et al. The Sikkim flood of October 2023: Drivers, causes and impacts of a multihazard cascade. Science.
Image Credits: Credit: Praful Rao

Keywords

Floods, Climate change mitigation, Climate change effects, Climate modeling, Geographic regions, Sediment, Remote sensing.