A glacier outburst is underway in Alaska. It could send a wave of water surging toward Juneau

CNN

3 days ago

A wave of water gushing out of an Alaskan glacier is threatening significant, potentially record-breaking flooding in Juneau for the third consecutive August.
'A glacial outburst has occurred at Suicide Basin. The basin is releasing and flooding is expected along Mendenhall Lake and River late Tuesday through Wednesday,' Juneau officials said in a Tuesday news release. 'Officials recommend residents in the 17ft lake level inundation zone evacuate the area until the flood waters recede.'
Glacial lake outbursts happen when a lake of melting snow and ice and rain 'drains rapidly — like pulling out the plug in a full bathtub' after pooling up so high it overtops the glacier that holds it back, according to the city of Juneau. In this case, it's due to the Mendenhall Glacier and its counterpart, dubbed Suicide Basin, which run up against the western portion of Juneau, about 10 miles from the city's center.
The National Weather Service issued a flood warning for the area Tuesday morning, noting the Mendenhall River, which runs along the west side of the city, will rise multiple feet Tuesday and Wednesday. The river is set to crest around 16.6 feet Wednesday afternoon, which would blow past the record level set just last August.
Last year's glacier outburst caused the river to surge to 15.99 feet, unleashing destructive flooding in Juneau that impacted more than 100 homes. 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.
Juneau installed a flood barrier along the area that was inundated in 2024, a city spokesperson told CNN. There are roughly 1,000 residents and businesses in that part of the city, but no mandatory evacuations are in place at this time, the spokesperson said. Officials are urging everyone in the inundation area to evacuate before river levels peak.
The Mendenhall River was very close to moderate flood stage — Level 3 of 4 — not long after the glacial outburst began late Tuesday morning. Major flood stage — Level 4 of 4 — is forecast to begin early Wednesday afternoon and continue until around midnight, local time, before water starts to recede on Thursday.
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. Part of the once icy expanse of the Suicide Basin has been replaced by an earthen divot that gets filled up like a bathtub each summer, setting the sequence in motion.
Rising temperatures have severely reduced the expanse of the Mendenhall Glacier and its Suicide Basin, creating the annual glacial lake outbreak hazard as ice gets replaced by liquid water.
CNN's Eric Zerkel and Amanda Musa contributed to this report.