A glacier outburst sent a surge of water downstream into Juneau. Flood barriers protected the city from disaster

A glacial outburst at Suicide Basin sent water rushing into Mendenhall Lake and River, prompting evacuation advisories as river levels approach record highs.

(CNN) — For the third consecutive year, a wave of water gushed out of an Alaskan glacial lake, threatening the state’s capital city of Juneau. But, flood barriers installed by the city managed to prevent disaster from unfolding in the picturesque port town despite record-breaking water levels this week.

The outburst began Tuesday at Suicide Basin, a glacial lake attached to the Mendenhall Glacier that runs up against the western portion of Juneau, about 10 miles from the city’s center. The basin formed as parts of its glacier melted and retreated and now acts like a giant bucket, filling up with rain, snow and ice that slowly melts over the summer.

Eventually, Suicide Basin gets so full that it escapes the surrounding ice of the Mendenhall Glacier. When that happens, water gushes out into the nearby Mendenhall Lake and eventually surges down the river.

The Mendenhall River, which flows along the west side of the city, eclipsed its previous record high level of 15.99 feet Wednesday morning after rising more than 7 feet in under 24 hours.

It crested at a new record of 16.65 feet Wednesday morning, according to the weather service, well above the previous record crest set just last August. River levels started dropping quickly not long after and by mid-afternoon the river had decreased to 10 feet. Lingering minor flooding will continue into Wednesday evening, but the river is expected to return to normal Thursday.

How flood barriers protected the city

While the Mendenhall River reached a new record high during this year’s event, the worst-case scenario was avoided largely due to flood prevention efforts made by state and local officials in response to past flooding.

A similar glacier outburst last year unleashed destructive flooding that impacted more than 100 homes in Juneau. City officials characterized the flood severity as “unprecedented.” The river level in 2024 topped the one reached during 2023’s early August glacial flood by a full foot.

Last year, a flood barrier was installed in flood-prone areas where roughly 1,000 residents and businesses reside, according to a city spokesperson.

Some of the resources that helped keep floodwaters at bay were provided by the Army Corps of Engineers earlier this year, an official said, including about 37,800 feet of HESCO barrier, which are sturdy modular bags filled with sand used to assist in blocking floodwaters – these bags are beneficial during natural disasters like flash flooding and hurricanes, according to HESCO’s website.

Over 100,000 sandbags were also used to mitigate flooding, according to Brig. Gen. Joseph Goetz, commander and division engineer for the US Army Corps of Engineers Pacific Ocean Division.

HESCO is a company that manufactures barrier systems. Local authorities have been working with the US Army Corps of Engineers to monitor the barriers.

“The HESCO barriers really have protected our community. If it weren’t for them, we would have hundreds and hundreds of flooded homes,” Juneau City Manager Katie Koester said at a news conference Wednesday afternoon.

Water was seeping through some of the barriers, but they had not been breached, according to a Wednesday morning update from the city.

“That being said, there still will be impacts, there still will be flooded homes and we will be working… to assess that damage and help our residents,” Koester added.

There were no rescues or incidents involving the water as Wednesday afternoon, according to Sam Russell, assistant fire chief for Capital City Fire/Rescue, which serves the city and borough of Juneau. Russell urged the public to stay away from any flooded areas until crews could assess the situation.

On Sunday, Alaska Gov. Mike Dunleavy issued a preemptive disaster declaration to better streamline emergency response efforts to the outburst.

“By issuing this declaration before the flood occurs, we can position state resources and personnel in advance to support local and tribal governments in their efforts to protect lives, homes, and essential services,” Dunleavy said in a statement. “Our goal is to act early to reduce impacts and preserve community safety.”

The capital of Alaska, Juneau has a population of about 33,000, according to the the US Census Bureau. The city is surrounded by coastal waters to the west and south.

Why does this keep happening?

The glacial lake outbursts have become a regular occurrence since 2011 and have worsened considerably each year since 2023.

They are yet another consequence of climate change due to fossil fuel pollution. The Arctic, including Alaska, is warming twice as fast as the rest of the planet as global temperatures rise.

This is causing glaciers, like these in Alaska, to thin or melt altogether.

Rising temperatures have severely reduced the expanse of the Mendenhall Glacier and its Suicide Basin, creating the annual glacial lake outburst hazard as ice gets replaced by liquid water and rises closer and closer to that “bathtub” edge throughout the summer.

Studies in recent years have shown that between 10 and 15 million people globally are exposed to impacts of glacial lake outburst flooding like what’s unfolding in Juneau.

Glaciers are melting and losing mass globally at an increasingly rapid rate as the world warms, producing more and larger glacial lakes, a 2024 study found. The uptick in number and size of glacial lakes is expected to increase the frequency of outburst flooding events in the future.

The-CNN-Wire™ & © 2025 Cable News Network, Inc., a Warner Bros. Discovery Company. All rights reserved.

Report a Typo