Alaska capital Juneau urged to evacuate as 'glacial outburst' flood looms
Because the flooding has been a growing concern, city officials have installed emergency flood barriers along several miles of riverbanks.
Emergency barriers protecting Alaska's capital city, Juneau, appear to be holding as summer glacial flooding driven by climate change threatens to inundate the area.
Authorities say water levels in the Mendenhall River were expected to crest around 8 a.m. Alaska time on Aug. 13. In an early-morning message, emergency managers said the 2 miles of barriers appeared to be working as planned to hold back the waters from Mendenhall Valley, where a majority of Juneau's 32,000 full-time residents live.
As of 6 a.m. local time − 10 a.m. ET − the river already had surpassed last year's record-setting flood level of 16 feet and was still rising, according to monitors at the National Weather Service. It was expected to crest at about 16.25 to 16.75 feet. After it crested, it would fall out of flood stage through Aug. 14, the weather service said.
"We have crews monitoring the areas closely and will continue to provide updates," city officials said in a statement posted to social media.
Officials said there were reports of "ponding water" in two areas, but the water represented minor seepage through the flood barriers and not a breach.
Forecasters had warned that some low portions of some roads would become impassable and that there was a chance of moderate to major flooding. Some homes along View Drive close to the river could see 1 to 2 feet of flooding, forecasters said.
Gov. Mike Dunleavy has issued a preemptive disaster declaration, citing the devastation caused by "glacial outbursts" in 2023 and 2024.
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. Floods in other years have swamped basements, destroyed infrastructure and collapsed buildings near the riverbanks. At least 290 homes were damaged by 2024 floodwaters, displacing residents, Juneau officials said. Some residents became trapped and had to be rescued, Dunleavy said.
A glacial outburst occurs when an ice dam holding back a lake – in this case Suicide Basin – collapses from the summer heat, releasing the water quickly. 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 in 2011, according to the National Weather Service.
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 considered most at risk for being overtopped. Although the new barriers are designed to hold back a flood of this potential magnitude, officials asked some residents to evacuate as a precaution.
Compared with the rest of the country, Alaska has warmed twice as quickly over the past several decades, and its average annual temperature has risen 3.1 degrees in the past century, according to the federal National Centers for Environmental Information.