Glacial dam outburst in Juneau, Alaska, erodes riverbanks, destroys at least 2 buildings

Raging waters that ate away at riverbanks, destroyed at least two buildings and damaged others had receded Monday in Alaska's capital city after an outburst of weekend flooding from a glacial lake, authorities said.

Levels along the Mendenhall River had begun falling by Sunday and returned to normal levels Monday but the city said river banks remained unstable.

On Sunday, onlookers gathered on a bridge over the river and along the banks of swollen Mendenhall Lake to take photos and videos though their ranks had thinned by Monday. A home was propped precariously along the eroded river bank as milky-coloured water whisked past.

Two homes were complete losses, and a third was partially destroyed, Robert Barr, Juneau's deputy city manager, said. There have been no reports of injuries or fatalities.

Additionally, two condo buildings with six units each and three homes were labeled as condemned though it's possible some of those could be salvaged, he said.

"We're hopeful that one or more of them may be able to undergo some substantial repairs, including bank stabilization," Barr said.

"It's not a foregone conclusion that those would be able to come back, but it's not impossible."

Other structures also sustained various levels of damage, he said. The city does not yet have either a monetary estimate of the damage or the total volume of water that was released into the river.

Such floods occur when glaciers melt and pour massive amounts of water into nearby lakes. A study released earlier this year found such floods pose a risk to about 15 million people worldwide, more than half of them in India, Pakistan, Peru and China.

Suicide Basin a side basin of the Mendenhall Glacier has released water that has caused sporadic flooding along the Mendenhall Lake and Mendenhall River since 2011, according to the National Weather Service. However, the maximum water level in the lake on Saturday night exceeded the previous record flood stage set in 2016, the weather service reported.

Water in the basin comes from sources such as rain and snowmelt and melt from the nearby Suicide Glacier, said Eran Hood, a University of Alaska Southeast professor of environmental science.

Nicole Ferrin, a warning coordination meteorologist with the National Weather Service, said that while it's not uncommon for these types of outburst floods to happen, this one was extreme.

"The amount of erosion that happened from the fast moving water was unprecedented," she said.

Water levels crested late Saturday night. Video posted on social media showed a home teetering at the edge of the riverbank collapsing into the river.

The Mendenhall Glacier in Juneau attracts hundreds of thousands of visitors each year but the awe-inspiring glacier continues to recede amid global warming.