Gangapurna glacier and lake is one of the top attractions of Manang Valley, Nepal. Image from Wikimedia Commons. License CC BY-SA 4.0.

This article was submitted as part of the Global Voices Climate Justice fellowship, which pairs journalists from Sinophone and Global Majority countries to investigate the effects of Chinese development projects abroad. Find more stories here.

In the towering Hindu Kush-Himalaya region — often referred to as the “Third Pole” — glaciers are melting at an alarming rate, threatening the lives and livelihoods of millions. Scientists estimate that up to 75 percent of the region’s glacier volume could vanish by the end of the century.

The Hindu Kush Himalaya stretches over 3,500 kilometers across eight countries, including Nepal and China. Image from Flickr. License CC BY-NC-SA 2.0.

As glaciers retreat, they often reveal deep hollows where ice once sat. These depressions begin to fill with meltwater, forming new glacial lakes. In other cases, small meltwater ponds emerge on the surface of debris-covered glaciers and gradually merge into larger lakes. These water bodies are not just passive byproducts of melting — they can also actively accelerate ice loss. As the lakes grow, they cause the glacier edges to break and melt more quickly, which in turn leads to even more lake expansion. Since 1990, glacial lakes around the world have expanded significantly in number, surface area, and volume — by approximately 53 percent, 51 percent, and 48 percent, respectively — and the trend is likely to continue throughout the 21st century.

While these glacial lakes are a vital part of regional hydrology in high mountain areas and contribute significantly to the flow of essential rivers such as the Indus and the Brahmaputra, which support life, agriculture, the economy, and essential ecosystem services in both their source regions and the areas downstream, they can also be extremely dangerous.

If the natural dams that hold them — often made of loose rock or ice — fail, they can unleash sudden and devastating Glacial Lake Outburst Floods (GLOFs), causing significant damage to property, infrastructure, and agricultural land, and resulting in extensive loss of life. However, the impact varies significantly across the world. For example, only 393 fatalities have been attributed to glacial lake outburst floods in the European Alps over the past millennium, while 5,745 deaths occurred in South America, and 6,300 in Central Asia.

The Thulagi glacier, located south-west of Mount Manaslu, in the Manang mountain range in the Himalayas, is slowly melting, transforming from ice into a lake. Image from Flickr. CC BY-NC-ND 2.0.

HKH: A region of extreme vulnerability

The Hindu Kush-Karakoram-Himalaya (HKH) range is one of the most vulnerable mountain systems globally to GLOF events. This vulnerability stems not only from the frequency and scale of the glacial lakes, but also from the large populations living downstream in high-risk zones.

According to recent studies, High Mountain Asia (HMA), which includes the HKH region, has the world’s highest GLOF exposure, with approximately 9.3 million people at risk — about 62 percent of the globally exposed population. 

Of the four highly populous countries accounting for more than half of this population, three are based in the HKH region: India, Pakistan, and China. India and Pakistan are rated as having the highest GLOF danger globally, not only due to the number and size of glacial lakes, but also because of their large and exposed populations.

Across the HKH region, researchers have recorded over 500 GLOF events in recent decades, many of them devastating. In 2020, a GLOF event in Jinwuco, China, unleashed an estimated 10 million cubic meters of water downriver. This destroyed villages, infrastructure, and an estimated 382.43 mu (25.5 hectares) of farmland. Wang Shijin, a researcher at the Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, explained to ScienceNet.com.cn, a Chinese-language science journal:

针对目前青藏高原冰湖溃决灾害增加的现象，随着气候变暖加剧、极端事件增加，雪/冰崩、冰川跃动、冰川洪水等冰冻圈失稳事件频发，进而激发了冰湖溃决事件的发生。在一定外因作用下，青藏高原极有可能再次发生溃决洪水灾害。

Regarding the current increase in glacial lake outburst disasters on the Qinghai-Tibet Plateau … with intensified climate warming and an increase in extreme events, cryosphere instability events such as snow/ice avalanches, glacier surges, and glacial floods are becoming more frequent, triggering the occurrence of glacial lake outburst disasters.

Other floods, like the 2013 Chorabari flood in India and the 2023 South Lhonak outburst in Sikkim, have caused extensive damage to infrastructure and communities.

The 2023 incident was a cascade of disasters, beginning with 14.7 million cubic meters of permafrost sliding into the South Lhonak Lake, which is located at 5,200 meters above sea level in Sikkim, India. According to researchers, the landslide generated a “20-meter tsunami-like impact wave,” which breached the natural dam and sent 50 million cubic meters of water cascading downriver. The ensuing flood picked up an estimated 270 million cubic meters of sediment and debris and carved a path of destruction 385 kilometers along the Teesta River, until it eventually reached Bangladesh. The disaster caused 55 deaths, displaced thousands, and destroyed millions of dollars’ worth of roads, buildings, and infrastructure, including the Teesta III hydropower dam and several other dams along the Teesta River. 

Given the extensive use of dams and hydropower in the region, the risk to hydropower stations is a real threat — and an expensive one. In 1985, a glacier lake flood destroyed the nearly-completed Namche Small Hydropower Plant, costing the Nepal government an estimated USD 1.5 million and delaying residents’ access to the expected energy output.

A ticking time bomb

GLOF risks are only increasing as warming global temperatures make glacial regions more unstable. According to experts, disasters in high mountain terrain are often chain reactions. Zhang Qianggong, head of the climate and environmental risks unit at the International Center for Integrated Mountain Development (ICIMOD), explains in an interview with Global Voices:

Maybe upstream, because of melting glaciers, a piece of ice fell into the glacial lake, causing waves, which eventually damaged the dam, triggering a GLOF. Then, along the way down, it triggers landslides, so it affects all areas within 10 kilometers. Mountain areas are very sensitive.

“It’s very hard to predict a GLOF,” says Zhang. The triggers are complex. A flood can start when landslides or ice chunks fall into the lake and create large waves; when heavy rainfall or rapid snow and glaciers melt overfill the lake; or when the natural dam — made of ice or loose rock — begins to weaken. However, because these events depend heavily on local conditions, it is very difficult to predict exactly when and where a GLOF might occur without detailed, on-the-ground research.

Yet the consequences are transboundary, not the result of a single-country problem. Xu Baiqing, a leading expert at the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, warns:

Whether in terms of water resource management or scientific and technological efforts, international cooperation is essential. It’s extremely difficult to carry out this kind of work unilaterally.

To tackle the growing risks of glacial lake outburst floods, research institutes like the Institute of Tibetan Plateau Research have adopted a multilayered approach. “The first step,” says Dr. Xu Baiqing, deputy director of the institute, “is to compile a comprehensive glacier lake inventory.”

This was achieved with support from European scientists, using integrated space-air-ground observation systems that now cover nearly the entire Himalayan region. Once the catalog was established, the next phase was risk identification. Whether a lake poses danger depends on multiple factors: the water volume, the structural stability of the moraine dam, and the potential downstream damage in case of a breach.

“This means that careful, multi-dimensional risk assessments are necessary,” he notes. For high-risk areas, it is essential to selectively build out a complete chain of systems: observation, early warning, and preventative infrastructure. All of this requires access to one essential currency in the information age: data.