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Juneau city officials ask some residents to leave area as glacial flooding nears
Water in a lake within the Mendenhall Glacier began overtopping an ice dam on Sunday, meaning a glacial outburst flood is days away
Officials in Alaska’s capital city are asking residents to voluntarily evacuate from parts of the Mendenhall Valley ahead of an expected glacial flood this week.
Last year’s flood damaged more than 290 homes in the valley, a largely suburban district of Juneau that is located near the Mendenhall Glacier, and while city officials have constructed temporary barriers to deter future flooding, those barriers haven’t yet been tested in an actual emergency.
“We are issuing those evacuation advisories, because although we are extremely confident in the HESCO barriers’ capability to protect neighborhoods, we’re not willing to bet on that with anybody’s life — or safety,” said Ryan O’Shaughnessy, director of emergency programs for the City and Borough of Juneau.
The Mendenhall Glacier Recreation Area, Alaska’s most-visited tourist destination, is preparing to shut down as well. The Nugget Falls Trail, the most-used pathway in the area, was closed to the public on Monday.
Officials from the U.S. Forest Service, which operates the glacier tourist site, did not participate in a media briefing Monday. Agencies at that briefing said the Mendenhall Glacier is short-staffed. The recreation site experienced widespread layoffs as part of a broader federal reduction in force earlier this year.
Late Sunday night, cellphones across Juneau rang with warning tones as city officials sent out an alert: Water has begun to overtop an ice dam that allows the creation of a glacial lake each summer.
Officials expect that within a week, the water will gush from the dam and into Mendenhall Lake, which lays at the glacier’s foot. From there, water will surge into the Mendenhall River and toward homes.
The first glacial outburst flood at Mendenhall Glacier happened in 2011, but the flooding was initially minor. Because the glacier is shrinking due to climate change, the floods have grown worse over time, culminating in last year’s disaster.
Aaron Jacobs, a hydrologist with the National Weather Service in Juneau, said this year’s ice dam is lower by 13 feet than it was last year, but the glacial lake — located in a place called Suicide Basin — contains about as much water as it did last year because melting ice elsewhere has increased the capacity of the basin.
“We’re expecting very similar volume estimates from last year,” he said.
That volume, about 16 billion gallons, weighs almost 67 million tons, the equivalent weight of 335 fully loaded container ships rushing through a normally placid river.
Eight inches of rain fell on and near the basin in recent days, Jacobs said, and hydrographs show that the level of Mendenhall Lake and River have risen.
That’s a little misleading: The lake and river will fall over the next few days as the rain diminishes, then will surge once the ice dam fails to contain the basin.
It isn’t clear how bad the resulting flood will be. That depends on things as varied as the tide, rainfall and the success or failure of the flood barriers.
O’Shaughnessy said officials will send out another emergency text alert to Juneau cellphones before the peak flood.
An emergency evacuation shelter has been set up at nearby Floyd Dryden school, and both state and local officials have issued preemptive disaster declarations as a precaution.
