The hidden danger of melting ice: 15 million people at risk

Nature · Published 19 October 2026 Swipe more like this →

In short: As glaciers retreat, they leave behind massive lakes held back by fragile dams of ice and debris. When these dams fail, they trigger glacial lake outburst floods (GLOFs)—catastrophic torrents that can arrive with almost no warning, threatening millions of lives downstream in a rapidly warming world.

Glacial lake outburst floods (GLOFs) are a growing global hazard driven by climate change. Global glacier mass has shrunk notably throughout the past thirty years, with annual losses during 2006 to 2016 calculated at -332 ± 144 Gt. This retreat uncovers 'overdeepenings' in former glacier beds, allowing meltwater to collect into new lakes. These lakes can create positive feedback loops: as they expand, they promote further ice loss through calving and subaqueous melting, which in turn creates more water and larger lakes.

The mechanics of a GLOF are complex and vary by geography. A dam breach can be triggered by mass movement-induced impulse waves, lake overfilling from rain or snowmelt, or the degradation of moraine and ice dams. For instance, a sub-glacial lake burst is specifically known as a jökulhlaup. Such occurrences occur with extreme speed; recorded peak flows reached 15,000 cubic metres per second, potentially transforming minor mountain creeks into 50-metre-deep torrents in mere minutes or days.

While the hazard is global, the risk is highly uneven. As of 2020, 15 million people (16.6% of those living in basins with glacial lakes) are identified as being in high-danger zones—specifically within 50 km of a lake and 1 km of a potential runout path. Four countries—India, Pakistan, Peru, and China—account for over half of this exposed population. In contrast, the European Alps have seen only 393 deaths from GLOFs over the last 1,000 years, while the Cordillera Blanca alone saw several thousand deaths in the last 70 years, illustrating how local geology and population density dictate the human cost.

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