A 'glacial outburst' prompted a flooding crisis in Alaska. What is that?
Glacial lake outburst flooding is a flood that's produced by the quick, unexpected release of water from a glacial lake.
Water from a melting glacier has caused a river near Alaska's capital city of Juneau to swell to historic levels amid a "glacial outburst" event that has prompted flooding fears and evacuations.
On Aug. 13, emergency barriers protecting Juneau appear to be holding, but the risk from summer glacial flooding is on the rise as climate change increases temperatures, causing more ice melt.
Glacial lake outburst flooding is a flood that's produced by the quick, unexpected release of water from a glacial lake.
These lakes can exist behind unsteady dams made of ice or bedrock, and when these dams fail, the water rushes out, often resulting in catastrophic downstream flooding.
A glacial outburst like the one in Alaska this week occurs when an ice dam holding back a lake – in this case Suicide Basin – collapses amid summer heat, releasing the water in a short period of time. Suicide Basin is part of the Mendenhall Glacier.
Aaron Jacobs, a hydrologist at the National Weather Service office in Juneau, said that as these events continue to unfold, scientists need to continue to improve their understanding of these glacial systems, especially as the climate continues to change and warm throughout Alaska.
Previous studies have tied glacier loss with climate change
Thanks to climate change, Earth's glaciers continue to melt away, losing up to 390 billion tons of ice and snow per year, a 2019 study said. The largest losses were glaciers in Alaska.
And a 2014 study found that since 1990, humans have been the primary cause of melting glaciers worldwide. In that study, researchers found that, from 1990 to 2010, about two-thirds of the world's glacier loss was due to rising temperatures from the burning of greenhouse gases, along with land-use changes.
"In our data we find unambiguous evidence of anthropogenic (human-caused) contribution to glacier mass loss," said study lead author Ben Marzeion, a climate scientist at the University of Innsbruck in Austria.
A 2023 study also found that millions of people worldwide are at risk of glacial lake outburst flooding, primarily in Asia.
Glacial outburst floods on the rise amid climate change
These glacial outbursts in Alaska are not a new phenomena and have been occurring annually in the Suicide Basin, sometimes more than once, since 2011. What is new in the last few years is the amount of water being released all at once during these events, which led to back-to-back years of record flooding downstream in Juneau in 2023 and 2024, according to the National Oceanic and Atmospheric Administration.
Compared to the rest of the country, Alaska has warmed twice as fast over the last several decades, and its average annual temperature has risen 3.1 degrees Fahrenheit in the past century, according to the federal National Centers for Environmental Information.
In other parts of the world, glacial outburst floods are also known as Jökulhlaups (an Icelandic word pronounced yo-KOOL-lahp), according to the National Park Service.