Ice dam at glacier releases floodwater toward downstream homes

A huge rainwater and snowwater pool by the Mendenhall glacier in Alaska began to release, and officials exhorted residents on Tuesday in parts of Juneau to evacuate before what could be a record of flood waters downstream.

In recent days, officials have warned people in the flood zone to be ready to evacuate. Tuesday morning, they confirmed that the water had started to escape the ice dam and sink downstream, with floods expected Tuesday evening until Wednesday.

The floods of the basin have become an annual concern and, in recent years, has swept away houses and overwhelmed hundreds of houses. Government agencies have installed a temporary tax this year in the hope of protecting itself against generalized damage.

“This will be a new record, based on all the information we have,” Nicole Ferrin, a meteorologist from the National Weather Service on Tuesday, at a press conference.

The Mendenhall glacier – a slimming and retired glacier which is a major tourist attraction in southeast Alaska – acts like a dam for the suicide basin, which fills each spring and summer with rainwater and snowfall. The basin itself was left behind when a smaller glacier withdrew.

When the pool water accumulates enough pressure, it makes its way under or around the ice dam, entering Lake Mendenhall and finally the Mendenhall river. Before the basin reaches the limit of its capacity and begins to exceed the weekend, the water level increased rapidly – up to 4 feet (1.22 meters) per day during the particularly sunny or rainy days, according to the National Weather Service.

The threat of flooding called explosions of glaciers has disturbed certain parts of Juneau since 2011. In some years, there have been limited floods of streets or properties near the lake or the river.

But 2023 and 2024 marked consecutive years of record floods, with the river last August, at 15.99 feet (4.9 meters), about 1 foot (0.3 meters) compared to the previous record established a year earlier, and floods extending further in the Mendenhall valley. The floods of this year were to be crest between 16.3 and 16.8 feet (4.96 to 5.12 meters).

Last year, nearly 300 residences were damaged.

A large explosion can release some 15 billion gallons of water, according to Southeast and Alaska Climate Adaptation Science Center from the University of Alaska. It is the equivalent of nearly 23,000 Piscines of Olympic size. During the flood last year, the flow in the Rushing Mendenhall river was about half that of the Niagara falls, according to the researchers.

City officials responded to the concerns of property owners this year by working with state, federal and tribal entities to install a temporary dike along 2.5 miles of river to try to protect themselves against generalized floods. The installation of around 10,000 obstacles to four feet (1.2 meters) high is intended to protect more than 460 properties against flood levels similar to last year, said Nate Rumsey, deputy director of the city engineering and public works department.

The body of American army engineers is at the start of what should be a process of one year of study of conditions in the region and to examine the options of a more permanent solution. The calendar has angry certain residents, who say that it is unreasonable.

The floods of the explosion should continue as long as the Mendenhall glacier acts as an ice dam to seal the basin, which could still extend from 25 to 60 years, according to researchers from the University and the Science Center.

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The writer Associated Press Becky Bohrer in Juneau contributed to this report.