Juneau, Alaska, Hit With Another "Glacial Outburst" Flood, But This Time They Fought Back

Barriers this year kept the worst of what has become
the annual glacial outburst flood this week
in Juneau, Alaska. You can see how badly
the houses in this photo would have been
flooded without the barriers. 

 Yearly summer events are often fun.

'The one in Juneau, Alaska is not.  

Once again, as has happened every August lately, parts of Alaska's capitol city are being hit by what is know as a glacial outburst flood. 

Such a flood happens when parts of a glacier melt, and water backs up behind rocks and/or ice. Finally the water breaks through, causing an often destructive flash flood. 

In Juneau, water from the melting glacier fills a hemmed in basin until the pressure grows strong enough to release a torrent of water from the Mendenhall Glacier and down the Mendenhall River into Juneau. 

Per the Washington Post: 

"By Wednesday morning, the floodwaters racing gown from what's called Suicide Basin has risen to record levels, faster than scientists had predicted the day before. 

Juneau officials warned residents to evacuate parts of the city that have been prone to repeated flooding."

It appears the flooding peaked Wednesday morning.    About 1,000 people had evacuated ahead of the flood. 

The Mendenhall River was already at minor flood stage because of heavy rains Sunday and early Monday. Since the river started at an elevated level, the gush of water from the glacier pushed the river Wednesday morning to 16.65 feet, which surpassed the record high level of 16 feet set during last August's glacial outburst.  

Since this has become a destructive, frustrating annual event, Juneau is trying to minimize the damage. 

This year, the city worked with the U.S. Army Corp of Engineers to build a massive wall of Hesco barriers along the river to prevent the destruction seen in the last two years, WaPo reports. 

Hesco barriers are durable cloth bags filled with dirt and sand and reinforce with a metal frame. They were often used by the military in places like Iraq and Afghanistan to fortify bases.  But they can be used as giant sandbags, too.

Early reports suggest the Hesco barriers mostly held, preventing much of the feared damage to homes near the river. Roads and streets were inundated, and some homes might have taken on a little water, but the damage appears to be much less than in the previous two years. 

The Hesco wall is expensive, and included big bills assessed to residents who live in flood zones.  There needs to be a more permanent solution, but the future of these floods is unpredictable. 

 The Juneau glacial outburst floods started in 2011 and have worsened in recent years. Climate change is helping to melt more glacial ice than in years past, so more water is now usually available to cause these August floods.

In August, 2023, the outburst flood destroyed several homes.  That event included dramatic video of a house collapsing into the river.  Last year, at least 300 homes were damaged by the flooding. 

It's possible that the nature of future summer glacial floods could change as more of the glacier melts, or the thawing gets even more intense in future years. Alaska has warmed twice as fast as any other state over the past few decades, and there's no reason why that trend won't continue, as areas closer to the Arctic are warming faster than places closer to the Equator. 

The Mendenhall glacial flooding could in upcoming years find another outlet, or burst out another way instead of blasting down the Mendenhall River in one big swoosh.  

Juneau - and many other parts of the world prone to glacial outburst floods in the age of climate change - need to stay on their toes. 

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. 

 

Alaska Glacial Flood Might Just Be A Foretaste Of Something Much Worse

A house tumbles into the Mendenhall River in Juneau,
Alaska last month after water from a melting glacier
burst through ice and roared down the valley. So
called glacial outburst floods are becoming more
common worldwide as glaciers melt under climate change. 

 You might have seen on the news last month a flood in Juneau, Alaska which included video of a house, having been undermined by raging water, toppled into the flooded river.  

This wasn't your average heavy rain flood. This was, at least in part, glaciers melting under pressure from climate change. 

In the Alaska incident, a melting glacier filled a valley with water, A high spot or chunks of glacier ice blocks the water, creating a lake. That natural dam can't hold, so eventually the water just pours out

According to Alaska Public Media:

"The basin drains like this every year. The glacier, which blocks its mouth, acts as a dam. Throughout the spring and summer, the basin fills with rain and meltwater until the water builds enough pressure to crack through the ice. Then it works its way through those cracks and out under the glacier, triggering the start of a glacial outburst flood.

Most years, the flooding has been minor. But this year, it tore through the Mendenhall Valley with more force than ever before gnawing through the riverbank and undermining homes that once seemed safe. Two homes were swept away completely, and dozens of people have been displaced."

For the longest time, a flood like what hit this river in Juneau couldn't have happened. This basin, or valley, was pretty much entirely filled by the glacier. With all that ice in the way, water couldn't collect there.

Over the years, the glacier receded under the unrelenting impact of our changing climate. Where the glacier once was, there is now a huge bowl shaped depression. In the summer, it rains, snow melts, and parts of the glacier melt further. This bowl fills up with water, basically turning into a lake. 

The glacial outburst floods started in 2011, but until this year, they haven't caused much damage. 

With more of the glacier melting, there's more and more room for the basin to fill up with a lot more water. This year, a lot of water collected before breaking through the glacier ice.

The result downstream was an unmitigated disaster.  It was by far the worst glacial outburst flood in Juneau's history.  The Mendenhall River flowed at six times its normal rate. The homes and buildings destroyed in the flood, some of which fell into the river, were originally 50 feet away from the river bank. 

"'Decades worth of erosion happened in one weekend,' Rick Thomas, Alaska Climate Specialist at the Alaska Center for Climate Assessment and Policy told Climate.gov. 'The buildings that fell into the river and those that are uninhabitable now, were not right next to the river on Friday afternoon."

Alaska Public Media again:

"(University of Alaska Southeast hydrologist Erin  ) Hood says the threat posed by glacial outbursts floods will hang over Juneau until the Mendenhall Glacier melts down to the point it can no longer dam the sin. That will likely take decades - and Hood would be surprised if Juneau doesn't see even worse floods before it happens."

Glacial outburst floods are by no means unique to Juneau, or Alaska for that matter. According to the Washington Post: 

"Some 15 million people worldwide live under the threat of sudden flooding from glaciers, according to a study published this year in the journal Nature Communications. As the climate warms, glaciers everywhere are retreating and meltwater lakes have grown in size and number, intensifying this threat." 

There have always been glacial outburst floods, but they are increasing as climate change accelerates the melt.  Runoff from the melting glaciers forms lakes behind ice, rocks or soil, just as it did in Juneau last month. Then the barrier breaks and sometimes tremendous flash floods result.

Some of the worst new glacial outburst floods have been in places like Pakistan, Nepal and China, parts of which are downstream from Himalayan glaciers. Parts of Peru, near the Andes, are also at risk.  

The number of glacial lakes and total area covered by those lakes have increased by 50 percent since 1990. Not all these lakes will produce dangerous outburst floods, but some inevitably will. 

I guess we add this to the list of a zillion hazards associated with climate change. 

One glimmer of good news: A cat named Leo was thought to be in a house that collapsed into the river in Juneau during the flood. However, the cat must have run out of the house when it heard it creaking before the collapse. Leo was just found safe, 26 days after the disaster. 

 Here news video of that house collapsing into the river. Click on this link to view, or if you see the image below click on that: