Major US city braces for potentially catastrophic glacial flooding as officials urge residents to evacuate

Emergency managers are urging residents of Alaska's capital, Juneau, to evacuate as glacial flooding from the Mendenhall River threatens to sweep through the city. 

Officials have recommended that residents within the 17-foot lake level inundation zone evacuate the area until the water recedes and an 'All Clear' message is sent via the wireless emergency alert system. 

In a Facebook post, officials said a glacial outburst has occurred at Suicide Basin, which is dammed by the Mendenhall Glacier that has experienced accelerated melting and retreat, primarily due to climate change.

'The basin is releasing, and flooding is expected along Mendenhall Lake and River late Tuesday through Wednesday,' they added. 

The river is expected to crest around 4pm local time on August 13 (8pm ET). 

Authorities are racing against the clock to protect Mendenhall Valley, where most of Juneau's 32,000 residents live. 

They are relying on two miles of emergency flood barriers installed just last month, though officials warn the swelling waters could overwhelm them.

A large glacial outburst can release as much as 15 billion gallons of water, the equivalent of nearly 23,000 Olympic-size swimming pools, according to the University of Alaska Southeast and the Alaska Climate Adaptation Science Center.

Nicole Ferrin, a meteorologist with the National Weather Service, said: 'This will be a new record, based on all of the information that we have.'

This is a developing story... More updates to come. 

Many roads, including Mendenhall Loop Road, have been closed, along with facilities along the Mendenhall Valley Public Library, Diamond Park Field House, Diamond Park Aquatic Center and fields located along the river.

'The closure will remain in effect until water levels recede below 12 feet and bridge engineers complete a safety inspection,' officials said. 

A Red Cross shelter was set up for residents at Floyd Dryden Gymnasium.