Juneau, Alaska Keeps Getting Flooded By Melting Glacier

A neighborhood in Juneau, Alaska inundated last week
by what is known as a "glacial outburst" flood.

 Last Tuesday, a melting glacier unleashed a torrent of water into neighborhoods in Juneau, Alaska, something that is becoming a summertime scourge in the state's capitol city. 

The water flooded about 100 homes and forced residents to flee through the frigid ice water to safety. 

If all this sounds familiar, it's because practically the same thing happened almost exactly a year later. You might remember the viral footage of a building in Juneau falling into the Mendenhall River after another flood, a type known as a glacial outburst. 

The term "glacial outburst" almost sounds like an oxymoron. Glacial evokes slowness, and outburst seems like it's something sudden. 

But follow me, here. 

The Mendenhall Glacier sits in the high elevations above Juneau. Especially in the past decade or so, a basin behind the glacier fills up with rainwater and melt from the glacier. The glacier acts like a dam to hold this lake back.

Until it doesn't

The pent up suddenly finds a way through, and the result is a flash flood in Juneau. That's what happened last Tuesday. 

Last year's version seemed more dramatic, but it only damaged or destroyed buildings right along the Mendenhall River's edge. This time, more water suddenly blasted down the hillsides than last year. That caused more widespread flooding and damaged houses further away from the river than in the 2023 event, the Washington Post reports. 

WaPo continues:

"Glacial outburst floods have poured out of Suicide Basin more than 30 times since 2011. It is challenging to predict exactly how large they will be, since conditions change each year. The jumble of icebergs in the basin keep melting - adding more liquid to the pool - and the glacier that acts as a dam keeps thinning and retreating as the atmosphere warms, so scientists don't know exactly when the pent-up water might release." 

Figuring out how much water will come out of the glacier during an outburst is hard to forecast, too. 

Scientists who are studying the glacier, and the basin - called Suicide Basin - where the water collects in the summer say year to year changes in the basin and the shape of the glacier make it difficult to determine how much water is dammed behind the glacier.

This year, the water in the basin wasn't has high as last year. But the basin is getting wider as the main glacier melts and gets thinner. The result was a greater volume of water in the basin this year that last.

This whole glacial outburst mess in Juneau - and elsewhere in the world - is of course tied to climate change. Mountain glaciers are melting all over the world, setting up similar temporary lakes behind glaciers in places like the Alps and the Himalayas. 

Those areas, too, are prone to glacial outbursts.