How a melting glacier is worsening floods in Alaska's capital Juneau

A torrent of water unleashed by a rapidly ailing glacier swelled an Alaskan river to unprecedented heights, triggering destructive flooding in the capital city of Juneau.

Over 100 homes along the Mendenhall River in the Mendenhall Valley have been either damaged or severely impacted by this massive glacial lake outburst, which city officials have labelled “unprecedented."

This disaster struck nearly a year after Juneau experienced a similar catastrophe that saw at least two homes collapse into the river and forced mass evacuations. Astonishingly, this year’s water levels surged more than a foot higher than last year’s devastating floods, raising alarm bells about the increasing frequency and severity of such incidents.

Why is glacial flooding becoming more frequent in this Alaskan city, and how is Juneau battling these relentless outbursts? Let’s dive deeper into the issue

What happened?

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The flooding in Juneau occurred because a smaller glacier near the Mendenhall Glacier had retreated, leaving behind a basin that was filled with rainwater and snowmelt each spring and summer.

The lake at Suicide Basin, which formed in this manner, was filled to the brim and overtopped the glacier on August 1, as city officials reported. This event followed an unusually wet July, with about twice the normal rainfall.

When the water in Suicide Basin created enough pressure, it forced its way under or around the ice dam formed by the Mendenhall Glacier. This water then flowed into Mendenhall Lake and eventually into the Mendenhall River, leading to significant flooding.

By Sunday it was clear water from the lake was reaching the river and by Monday city officials warned residents in Juneau that they might need to evacuate.

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Water levels in the Suicide Basin lake dropped more than 400 feet after this year’s outburst, including a dramatic drop of more than 350 feet within 24 hours from Monday to Tuesday.

According to the National Weather Service, all that release of water caused the Mendenhall River to skyrocket to a record-breaking 15.99 feet on Tuesday morning, a foot higher than what it was during last year’s deluge. However, Juneau Deputy City Manager Robert Barr told the _Associated Press, t_hat there was “a lot more water in the valley, on the streets, in people’s homes.”

Destruction in Juneau

In Juneau, around 100 homes and several businesses suffered damage when floodwaters surged to alarming levels early Tuesday morning.

Alaska’s emergency management agency shared dramatic photos on Facebook, depicting homes engulfed by murky water that rose high enough to submerge vehicle hoods. In some neighbourhoods, cars were seen floating, while residents scrambled to evacuate.

Debbie Penrose Fischer, a local, recounted to AP that her daughter, Alyssa, who lives just across the street, reported the water reaching her hips at one point.

According to Barr, some streets were overwhelmed by 3 to 4 feet of water, possibly even more. Fortunately, despite the severity of the flooding in the city of 30,000, there were no reported injuries. Alaska Governor Mike Dunleavy issued a disaster declaration to support response and recovery efforts.

“I am grateful no one has been injured or killed by this morning’s outburst flood,” Dunleavy told CNN. “Emergency responders and managers have done an outstanding job keeping their residents safe.”

Authorities had set up an emergency shelter for those evacuated, which accommodated around 40 people overnight, reported AP.

Although the floodwaters have receded now that the glacial lake is no longer at capacity and the river has dropped below flood stage, the aftermath is stark. Piles of garbage bags, wood, boxes, and soaked insulation, and carpeting litter the curbs. Street sweepers are now working to clear the gray, silty residue left behind by the retreating waters.

How climate change is worsening floods

Since 2011, glacier outbursts have surged in frequency, a direct consequence of climate change. According to the National Oceanic and Atmospheric Administration, the Arctic, including Alaska, is experiencing warming at twice the global average rate due to increased fossil fuel emissions.

This accelerated warming causes glaciers to thin and melts more rapidly, destabilising glacial lakes. For example, the Mendenhall and Suicide glaciers, which have been sources of recent floodwaters, are experiencing significant retreats increasing the risk for glacier lake outburst floods.

According to a 2021 report by the Intergovernmental Panel on Climate Change, the ongoing rise in global temperatures is intensifying the risk of glacier lake outburst floods, highlighting the severe impacts of climate change on glacial systems and the increased frequency of extreme weather events. 

With input from agencies