Glacial lakes are found everywhere glaciers are found. The water is held in place by dams of glacial ice or by rocky deposits that the glacier itself put in place. With the earth's temperatures rising, these natural dams are more likely to fail. The ice becomes thinner while the amount of water rises until the dam gives way. The floods this causes are larger and more violent than floods caused by excess rain or snow because they dump an enormous amount of water in a short time. There are 15 million people around the world living in the danger zone below these glacial lakes, and thousands have been killed by the outburst floods in the past few years. Their force can inundate towns with water, rocks, and ice for many miles downstream.
Juneau, Alaska, is in the flood plain of the Mendenhall Glacier, but had never experienced an outburst flood before 2011. Now they happen several times a year. The latest flood in August sent 14 billion gallons of water to Juneau, flooding homes that were so far from the Mendenhall River that the residents never expected to be flooded. Read about the new phenomenon of glacial lake outburst floods at Smithsonian.
(Image credit: The National Guard)
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It's kind of surprising that, with the example of the Pacific Northwest sitting in their face, people still didn't recognize the risks of glacial lakes.Admittedly, there was no human record to flog it across newspapers, since it happened 12,000 years ago, but the collapse of the glacial dam that formed Glacial Lake Missoula and, separately, Glacial Lake Columbia, created the Channeled Scablands across Idaho, Washington, and Oregon. But I suppose if you don't live in the region, or watch the lectures given by Nick Zentner on the geologic history of the Pacific Northwest, all of that will just run under your radar.
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