Authorities in Alaska’s capital, Juneau, are urging residents to evacuate as record floodwaters are expected to surge downstream from a basin dammed by the Mendenhall Glacier. Officials warn the event, driven by climate change and glacial retreat, could be the most severe on record.
The annual summer flooding, known as a glacial lake outburst flood (GLOF), occurs when water trapped by the glacier’s ice dam escapes. This year’s event is fuelled by a combination of rainfall and snowmelt, threatening large parts of the city.
The Mendenhall River is forecast to crest at over 16ft on Wednesday morning, according to the National Weather Service (NWS), which said recent heavy rainfall had complicated predictions. Authorities hope newly installed emergency flood barriers will protect the Mendenhall Valley, home to most of Juneau’s 32,000 residents.
On Tuesday morning, officials confirmed that water had begun to escape from Suicide Basin, the source of the floods, with levels expected to peak by Wednesday afternoon. Residents in the flood zone have been told to evacuate immediately.
“This will be a new record based on all of the information we have,” said Nicole Ferrin of the NWS, adding that the release of water beneath the glacier had already begun.
Since 2011, annual outburst floods from Suicide Basin have poured into Mendenhall Lake before rushing down the river towards Juneau. The phenomenon has intensified due to climate change, with Alaska’s average temperature having risen 3.1F over the past century, twice the national average, according to the National Oceanic and Atmospheric Administration (NOAA).
What scientists say about Alaska’s glaciers
Scientists say Alaska’s glaciers are among the fastest-melting in the world, with the Mendenhall Glacier receding by 100 to 150 feet each year. Rick Thoman, a climate specialist at the Alaska Center for Climate Assessment and Policy, said: “Without climate change, there is no reason to think that this would be happening on the Mendenhall Glacier, then in the lake, and downriver.”
A similar outburst in August 2023 sent unprecedented water levels into areas of Juneau that had never flooded before, causing severe erosion and property damage. In recent years, the floods have swept away houses and inundated hundreds of homes.
