Ask folks who live near the Mendenhall River and they’ll likely be able to tell you exactly where they were the day billions of gallons of glacial melt water flooded their neighborhoods last year.
Inquire with local elders and it’s likely few remember the river ever reaching such heights.
Entire spruce trees were uprooted by force of the water, trails were eroded away and thrill-seeking kayakers rode standing waves in a river raging at flood stage.
It was a deluge, an outpouring, a jökulhlaup.
It’s pronounced “yoke-a-loop,” and according to Eran Hood, associate professor of environmental science at the University of Alaska Southeast, it’s an Icelandic term used to describe when water, trapped within or around a glacier, often as a result of nearby volcanic activity, is released.
“I prefer to call it a glacial outburst flood,” Tom Mattice said.
That’s accurate too, according to Hood. Perhaps more so, he said, since volcanic activity played no role in last year’s event.
Mattice, who works as the City and Borough of Juneau’s emergency program manager, Hood and Aaron Jacobs, a hydro focal points specialist with the National Weather Service Juneau office, were on the forefront of the action last year.
Jacobs said his respect for the forces of nature went up a few notches when he first saw the “drained” basin above the Mendenhall Glacier — the source of the flood. Mattice likened it to the bowl-shape one would find in a recently-drained sink that had held water and ice cubes.
Tonight, the trio will conduct a presentation beginning at 6:30 p.m. at the Mendenhall Glacier Visitor Center on the glacial outburst flood that happened on July 21 of last year.
Mattice said the talk will cover everything from how the events transpired to some of the findings that Hood and his students have uncovered in the field.
One of the things they know now, that they didn’t know then, is the amount of water that drained from the basin that day.
“The number is in the billions of gallons,” Jacobs said.
And while a glacial outburst of that magnitude doesn’t happen every day on the Mendenhall, or even every year, it happens more frequently than people realize. Jacobs, who monitors water levels on rivers throughout the region, said smaller outbursts have happened throughout the years. In the summer, he said, it’s likely they happen all the time, though none are large enough to present a problem. Some, he said, are barely a blip on his data sheet.
In other parts of Southeast, Mattice said they happen quite regularly. The Tulsequah and Alsek rivers, for instance, see this type of flooding annually.
Glacial outburst floods are more frequent in areas where glacial change exists. In other words, areas where glacial recession has resulted in melting water that pools are more likely to have an event occur.
Today, researchers better understand some of the factors that led to last year's flood.
“Suicide Basin used to have a glacier pushing into it, pushing right into the Mendenhall Glacier, and now that glacier is somewhat dead and receding,” Mattice said. “The Mendenhall Glacier is growing past the face of it and so we’re seeing a little more water pooling in that basin and if that drainage area for the water gets plugged, you have buildup. Hopefully, at some point it releases, obviously sooner rather than later, but that’s what causes the rise in river levels.”
Sounds simple enough, though when it comes to prediction and mitigation, that’s another story.
“It’s hard to say, but the way that it’s set up, it looks like it will very likely happen again. And it could be recurring regularly,” Hood said. “The conditions that set up for this type of thing to occur, is when you have a side glacier that pulls back away from the main glacier. Where it comes down, there is a depression that can fill up with water, so the main glacier begins to act like a dam. Its certainly not the only way it can happen, but its a common mechanism.”
“When it fills up with enough water, it basically lifts up the main glacier and starts the drainage event. Once there’s enough pressure, it makes the main glacier somewhat buoyant, and once the water starts draining out, the water moving will generate friction, and that heat generated by the friction of the water, will make the drainage occur faster and faster.”
Mattice said he and others are working on ways to better monitor the water levels in the basin and to forecast when the potential for a flood is growing.
“Unless we go up there and melt the Mendenhall Glacier with a blow torch, it’s going to happen again,” Mattice said. “We’re not going to be able to stop it. But understanding when the water is building up in the basin and understanding how much water is in the basin will (bring officials to) a heightened state of awareness so we can communicate with the public when danger might be rising.”
He said officials and researchers have explored ways to monitor the area.
“We’re trying to put in some camera monitoring systems that have some real-time monitoring back in town so we can look and see if there’s water in the basin and get an idea of how much,” Mattice said.
Other ideas to help with monitoring are a frequent communication schedule between glacier guiding companies and officials, and putting marks in Suicide Basin to monitor water levels.
In the meantime, Jacobs said events like a glacial outburst flood can be pretty exciting for researchers.
“It’s a bit of a double-edged sword,” he said. “On one hand it’s exhilarating to see Mother Nature at work, but then there’s the task of letting people know about the event so they can stay out of danger.”
• Contact Outdoors editor Abby Lowell at firstname.lastname@example.org.