Some Juneau residents urged to evacuate as Alaska's Mendenhall Glacier releases floodwater

NBC News

3 days ago

Residents in some parts of Juneau prepared to evacuate ahead of what could be a record surge of flooding as rainwater and snowmelt in a huge basin dammed by Alaska's Mendenhall Glacier started to flow downstream toward the capital city.
Officials in recent days have been warning people in the flood zone to be ready to evacuate. On Tuesday morning they confirmed water had started escaping the ice dam, with flooding expected late Tuesday and on Wednesday. They advised people in the city's flood zone to leave.
The Mendenhall Glacier is about 12 miles from Juneau and is a popular tourist attraction due to its proximity to Alaska's capital city and easy access on walking trails. Homes on the city's outskirts are within miles of Mendenhall Lake, which sits below the glacier, and many front the Mendenhall River.
The water that's being released in the glacial outburst is flowing into the river, putting homes that are closest to the river at risk. The National Weather Service said it expected flooding to peak at 4 p.m. local time Wednesday.
'This will be a new record, based on all of the information that we have,' Nicole Ferrin, a weather service meteorologist, told a news conference Tuesday.
Flooding from the basin has become an annual concern, and in recent years has swept away houses and swamped hundreds of homes. Government agencies installed temporary barriers this year in hopes of protecting several hundred homes in the inundation area from widespread damage.
The thinning, retreating glacier in southeast Alaska acts as a dam for Suicide Basin, which fills each spring and summer with rainwater and snowmelt. The basin itself was left behind when a smaller glacier nearby retreated.
When the water in the basin builds up enough pressure, it forces its way under or around the ice dam, entering Mendenhall Lake and eventually the Mendenhall River.
Before the basin reached the limit of its capacity and began overtopping, the water level was rising rapidly — as much as 4 feet per day during especially sunny or rainy days, according to the National Weather Service.
The threat of so-called glacier outburst flooding has troubled parts of Juneau since 2011. In some years, there has been limited flooding of streets or properties near the lake or river.
But 2023 and 2024 marked successive years of record flooding, with the river last August cresting at 15.99 feet, about 1 foot over the prior record set a year earlier, and flooding extending farther into the Mendenhall Valley. This year's flooding was predicted to crest at between 16.3 and 16.8 feet.
Last year, nearly 300 residences were damaged.
A large outburst can release some 15 billion gallons of water, according to the University of Alaska Southeast and Alaska Climate Adaptation Science Center. That's the equivalent of nearly 23,000 Olympic-size swimming pools. During last year's flood, the flow rate in the rushing Mendenhall River was about half that of Niagara Falls, the researchers say.
City officials responded to concerns from property owners this year by working with state, federal and tribal entities to install a temporary levee along roughly 2.5 miles of riverbank in an attempt to guard against widespread flooding. The installation of about 10,000, four-foot tall barriers is intended to protect more than 460 properties from flood levels similar to last year, said Nate Rumsey, deputy director with the city's engineering and public works department.
The U.S. Army Corps of Engineers is at the start of what's expected to be a yearslong process of studying conditions in the region and examining options for a more permanent solution. The timeline has angered some residents, who say it's unreasonable.
Outburst floods are expected to continue as long as the Mendenhall Glacier acts as an ice dam to seal off the basin, which could span another 25 to 60 years, according to the university and science center researchers.