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Millions of People at Risk of Glacial Lake Floods, Study Finds

In 2020, a massive landslide on the coast of British Columbia reshaped a swath of the landscape by propelling 7.7 million cubic meters of debris into an ocean inlet, CBC News reported. The force was equivalent to a 4.9-magnitude earthquake, and it was the end result of a domino-like sequence of events—starting with a slope that crashed down into a swollen glacial lake, triggered an outburst flood that launched a tsunami wave down a mountain.

While no one was hurt in the event, the landslide was linked to the recession of the West Grenville Glacier, which has retreated 4 kilometers (2.5 miles) over the past 200 years, according to the Columbia Climate School. “It is only the latest such occurrence in a warming world where mountain glaciers are rapidly pulling back and creating conditions ripe for such collapses,” a press release from the school noted.

As glaciers melt, they pour massive amounts of water into nearby lakes, which can trigger landslides and deadly flooding. A new study published in Nature Communications found that 15 million people worldwide live under the threat of a sudden outburst flood, and more than half of those at-risk people live in just four countries: China, India, Pakistan, and Peru.

Glacial lake outburst floods (GLOFs) “can be highly destructive and can arrive with little prior warning, causing significant damage to property, infrastructure, and agricultural land, and resulting in extensive loss of life,” the study said. “However, the impact varies significantly across the globe; in the last 70 years, several thousand people have been killed by GLOFs in the Cordillera Blanca (mountain range in Peru) alone, most from a small number of events, while only 393 deaths in the European Alps can be directly linked to GLOF activity over the last 1,000 years.”

One of the most devastating glacial floods was in Peru in 1941, and it killed between 1,800 and 6,000 people. In India, heavy rains and a GLOF combined to kill thousands of people in 2013, the Associated Press reported.

While scientists say that climate change has not made these floods more frequent, it is causing glaciers to shrink, melting more water into lakes, and increasing the danger in situations when dams burst. Since 1990, the number, area, and volume of glacial lakes have grown rapidly (by 53 percent, 51 percent, and 48 percent respectively).

Measuring risk to humans from GLOFs depends on a number of factors: climate, geography, population, and vulnerability. Glacial basins near low or no human populations (like the West Grenville Glacier in British Columbia) pose limited risk to people. But the Khyber Pakhtunkhwa basin in Pakistan poses a risk to 1.2 million vulnerable people who live in a valley below the glacial lake.

The United States and Canada have three lake basins that pose a high risk (in Alaska’s Kenai Peninsula, northeast Washington state, and west central British Columbia), but relatively few people are in danger zones.