Alaska Capital Braces as Glacial Dam Breaks Again

Juneau's 32,000 residents watched nervously Tuesday morning as the Mendenhall River surged past last year's record 16-foot flood level, threatening to swamp Alaska's capital city for the third straight summer.

Emergency flood barriers installed along two miles of riverbank appeared to be holding as of 10 a.m. ET, with only minor seepage reported. But the river kept rising toward an expected crest of nearly 17 feet—testing whether the new defenses could handle what climate change keeps throwing at this city.

When Ice Dams Can't Hold

This isn't normal flooding. It's what scientists call a "glacial outburst"—when summer heat causes an ice dam to collapse, releasing an entire lake's worth of water at once.

In Juneau's case, Suicide Basin fills with meltwater behind the Mendenhall Glacier. When the ice dam fails, billions of gallons rush downstream into the Mendenhall Valley, where most of the city's residents live.