Nepal tragedy highlights a growing threat: 15 million people live at risk from glacial lakes

The catastrophic Tibet-Nepal flood, which has left hundreds dead and thousands missing, has drawn renewed attention to the risks of living in mountain regions with glaciers, as all indications suggest that the disaster was triggered by the collapse of one of these ice masses. The phenomenon is known as a GLOF, or glacial lake outburst flood, a sudden flood caused by the breaching of a glacial lake.

Climate change and rising temperatures are fueling these events: such floods have become six times more frequent over the past century. Major mountain ranges such as the Himalayas, the Andes and the Alps are among the areas most exposed to these disasters. An estimated 15 million people worldwide live at risk from glacial lake floods, half of them in Peru, India, China and Pakistan. Monitoring glaciers and glacial lakes is no easy task, especially in developing countries, but it saves lives: last year, a Swiss village was evacuated two days before the collapse of another glacier.

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From the beginning of the 20th century to the 2010s, the annual average number of documented GLOFs increased nearly sixfold, rising from 7.6 per year in the first decade of the century to 43.7 in the 2010s.

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The historical GLOF database compiled by the University of Vienna has identified 3,151 glacial lake outburst floods between the years 850 and 2022 across 27 countries. Most have occurred in North America (833), Central Asia (569), the Alps (443) and the Andes (337). It should be noted that in some of the world’s most remote mountain regions, such as the Andes and the Himalayas, GLOFs were harder to document before the advent of satellite imagery. In fact, it is still unclear which glacial lake burst after the glacier collapse in Tibet.

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How can future disasters be prevented? Jesús Revuelto [a researchers at the Pyrenean Institute of Ecology, IPE-CSIC] points to an example from Europe: “Switzerland did it last year in Blatten. They monitored the glacier and slopes with sensors, seismic equipment… They found major displacements and evacuated the village two days before a huge flood.”

In the Alps, resources are available to closely monitor glaciers and other unstable ice masses. In developing countries such as Nepal, India and Pakistan, however, the challenge is far greater. “There are more potentially dangerous areas and steeper slopes, so it is difficult to monitor all the mountains. But at the very least, we should have identified and mapped the areas that are susceptible to this type of landslide, as well as the valleys where they might end up,” he concludes.

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“Because many Himalayan rivers cross national boundaries, nations will have to work together to strengthen data sharing, joint monitoring and coordinated early-warning systems,” write two researchers at the Monash University in Melbourne, Australia.

The task is increasingly urgent, they argue.

“Climate change is loading the dice for more disasters in this high, cold region.”

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