Glacial break causes major flooding in Alaska, officials issue emergency declaration

City officials in Juneau, Alaska, have issued an emergency declaration as a glacier lake outburst flood wreaks havoc near the city, where structures have been destroyed.

The flooding is due to a break on Suicide Basin, a side basin on the Mendenhall Glacier, located about 12 miles north of Alaska’s state capital. A glacial lake outburst flood occurs when a dam containing a glacial lake breaks.

Glacial break causes major flooding in Alaska, officials issue emergency declaration

Screen grab of a video showing the collapse of a home into the Mendenhall River in Alaska on Saturday, Aug. 5, 2023.

Sam Nolan

The flooding has destroyed several structures along the Mendenhall River, according to the National Weather Service. Two homes have been lost and another partially damaged and washed away, Rob Barr, deputy city manager of Juneau, told ABC News.

“A handful” of other residences, including a condo building that is “significantly undermined,” are at risk, Barr said.

Trees and debris are currently littering the river, according to the NWS, which described the flooding as an “extreme” event.

On the FEMA scale, there was less than a 1% chance of that level of flooding occurring, National Weather Service Juneau hydrologist Aaron Jacobs said.

“We didn’t even think that this was possible,” Jacobs said.

PHOTO: Mendenhall Glacier in Alaska.

Mendenhall Glacier in Alaska.

Planet One Images/Universal Images Group via Getty Images, FILE

Video taken by resident Sam Nolan shows a multi-story structure collapsing into the river. Nolan watched for more than an hour as the home succumbed to the floodwaters, he said.

“It was really sad to see, but all we could do was stand there and watch,” Nolan said.

Other videos taken by residents show debris and trees floating in Mendenhall River close to Juneau International Airport.

The Mendenhall Lake level crested at 14.97 feet on Saturday around 11:15 p.m. local time, well above the previous record of 11.99 feet in July 2016. Significant flooding was reported in areas that previously have not seen flooding, and there has been significant erosion along the riverbanks, according to the NWS.

PHOTO: Map indicating the location of Suicide Basin, a side basin of the Mendenhall Glacier above Juneau, Alaska. Since 2011, Suicide Basin has released glacier lake outburst floods that cause inundation along Mendenhall Lake and Mendenhall River.

Map indicating the location of Suicide Basin, a side basin of the Mendenhall Glacier above Juneau, Alaska. Since 2011, Suicide Basin has released glacier lake outburst floods that cause inundation along Mendenhall Lake and Mendenhall River.

National Weather Service/National Oceanic and Atmospheric Administration

Waters have been falling at a rapid pace of .7 feet per hour, but flooding is ongoing, the NWS said.

The flooding has closed several roads in the region, including bridges, according to the city of Juneau.

City emergency operations urged residents to stay away from the river during the duration of the flood event.

PHOTO: Mendenhall Glacier in the Tongass National Forest near the city of Juneau, Alaska, July 6, 2021.

Mendenhall Glacier in the Tongass National Forest near the city of Juneau, Alaska, July 6, 2021.

Salwan Georges/The Washington Post via Getty Images, FILE

Suicide Basin has been releasing glacier lake outburst floods that cause inundation along Mendenhall Lake and Mendenhall River since 2011, according to the National Weather Service.

The risk of flooding from melted glaciers to increase as climate warms, a study published in Nature Climate Change in 2021 found.

ABC News’ Helena Skinner and Samira Said contributed to this report.

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