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: