Alaska capital Juneau urged to evacuate as 'glacial outburst' flood looms

[Desmond Milligan 0]

Emergency managers are urging many residents of Alaska's capital city of Juneau to evacuate as summer glacial flooding driven by climate change threatens to inundate the area.

Authorities say flooding from the Mendenhall River will likely crest around 4 p.m. Alaska time on Aug. 13, or 8 p.m. Eastern. They hope two miles worth of emergency flood barriers they finished intalling last month will hold back the waters from Mendenhall Valley, where a majority of Juneau's 32,000 full-time residents live.

"Residents are advised to evacuate the potential flood inundation area," City and Borough of Juneau officials said in a message Aug. 12. "Do not go near the river."

Gov. Mike Dunleavy has also issued a preemptive disaster declaration, citing the devastation caused by "glacial outbursts" in both 2023 and 2024.

As of noon Alaska time on Aug. 12, the Mendenhall River in Juneau had risen to 10 feet deep from its usual level of about 5 feet, crossing into "moderate" flood stage territory, the National Weather Service reported. The record set last year is 16 feet deep, and forecasters say the river could surpass that.

Forecasters estimate 14.6 billion gallons of water were released during last year's flood, enough to fill more than 22,000 Olympic-sized swimming pools, according to the weather service. Previous years floods have swamped basements, destroyed infrastructure and collapsed buildings near the riverbanks.

A glacial outburst like this occurs when an ice dam holding back a lake - in this case Suicide Basin - collapses from the summer heat, releasing the water in a short period of time. Suicide Basin is part of the Mendenhall Glacier, a popular tourist destination easily reached from Juneau.

Federal scientists say climate change is causing the glacier to melt faster, along with altering rainfall patterns, exacerbating the danger. The first recorded outburst flood from the glacier happened 2011, according to the National Weather Service.

This Aug. 6, 2024, photo provided by the Alaska Division of Homeland Security and Emergency Management shows the extent of flooding caused by the Mendenhall Glacier outburst, which is taking place in 2025 around Aug. 12-13.

Because the flooding has been a growing concern for Juneau over the past several years, city officials with federal assistance installed emergency flood barriers along several miles of riverbanks in the areas deemed most at risk for being overtopped. Although the new barriers are designed to hold back a flood of this potential magnitude, officials have asked residents to evacuate as a precaution.

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.

This article originally appeared on USA TODAY: 'Glacial outburst' threatens Alaska city, prompts evacuations

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