One of Lance Goodwin’s pilots noticed something strange as he flew over the Slims River a few weeks ago. He told Goodwin about it when he landed, and the next day, they went out together to take some photos.
The Slims River, they discovered, isn’t really a river anymore. It’s more of a trickle.
And since Goodwin posted the photos online, the discovery has made geologists and glaciologists excited to study a phenomenon they don’t get to witness all that often.
The Slims River, now officially called the A'ay Chu, is largely fed by meltwater from the Kaskawulsh glacier, which has flowed out into both the Slims and the Kaskawulsh rivers for the last few hundred years.
But this year, something has shifted as the glacier retreats. And now, almost all the water is flowing into the Kaskawulsh River and from there into the Alsek, leaving the Slims River valley dusty and dry.
The process is called river piracy, and it wasn’t a gradual change. Goodwin, who owns Icefield Discovery, a local glacier flightseeing company, said the Slims was flowing well in April. But by the end of May, suddenly, everything was different.
“You can see water, but it’s definitely not much for a flow out of the glacier itself,” he said.
The Slims River is the major tributary of Kluane Lake, and Goodwin said the change is already having a noticeable impact on the lake. The water level is low, and boat launches at Burwash Landing, Destruction Bay and Sheep Mountain are drier than usual.
“It’s hard to get access to the water right now for putting in boats,” he said.
On top of that, there’s the dust. On hot days, especially, the wind kicks up dust in the river valley and blows it across the Alaska Highway. Goodwin said it’s been bad enough on a couple of days that he’s chosen not to fly.
This isn’t the first time Goodwin’s seen something like this. He can remember one instance, 15 or 20 years ago, when most of the water from the glacier shifted over into the Kaskawulsh River. The next year, the Slims was flowing normally again.
“It can switch anytime it wants,” he said. “You can’t say when it’s going to happen.”
But this year does seem to be different, according to researchers.
Even when there have been changes in the recent past, the Slims has always had some water running through it, said Luke Copland, a glaciologist at the University of Ottawa who studies the Kaskawulsh glacier. This time, that’s not the case.
“It seems that the Slims has essentially gone down to a trickle,” he said. “There’s really nothing there right now.”
It seems likely that the retreat of the glacier is related to the new flow of water into the Kaskawulsh River. A decade ago, a group of scientists published a paper predicting exactly what seems to be happening now.
“Retreat of Kaskawulsh Glacier … is leading to a situation in which drainage is likely to be captured into the steeper Kaskawulsh River in the future,” they wrote.
Kristen Kennedy, a surficial geologist with the Yukon Geological Survey, agreed that there’s nothing really surprising about what’s happening now.
In fact, the whole system may simply be reverting to how it looked more than 300 years ago.
For most of the period since the end of the last Ice Age about 10,000 years ago, the Kaskawulsh glacier ended several kilometres higher up than it does today, and drained entirely into the Kaskawulsh River, Kennedy explained.
Kluane Lake was 30 metres lower than it is today, and it drained into the Slims River, toward the glacier.
But about 300 years ago, global temperatures cooled dramatically during what’s known as the Little Ice Age. At that time, the glacier surged forward and forced the Slims River to change direction, raising Kluane Lake to 12 metres above its present level. Eventually, the lake spilled over and formed the Kluane River, and the system settled into its present form.
Now, the glacier’s shrinking back again, and the steeper Kaskawulsh River may be regaining its former glory as the sole outflow from the glacier.
“This is geology in action,” Kennedy said. “This was the status quo 300 years ago and in geological time, 300 years is the blink of an eye.”
Still, it’s too early to say whether this will be the permanent change that scientists have predicted, or whether it’s just another temporary shift.
But if it is permanent, the scientists don’t seem too alarmed. Thus far, they’re not predicting any catastrophic effects, though it’s not great news for any fish that called the Slims River home.
“Over the long term, we’ll expect the bottom of the river valley to become all vegetated,” Copland said. Kennedy added that it will be interesting to monitor changes to the Slims River delta now that there’s no water to deposit the tonnes of sediment that have been building up there over the last few hundred years.
But as to whether this shift is yet another example of manmade climate change, Kennedy was ambivalent. The Kaskawulsh glacier has been retreating since the end of the Little Ice Age, after all.
“Would this particular event have happened without anthropogenic climate change? Probably,” she said.
“It’s neat to see. It’s really just an interesting natural phenomenon that’s happening right before our eyes, and not very many people get to see something like this.”
Carmen Wong, a Parks Canada ecologist in Kluane National Park and Reserve, said the changes to the Slims River shouldn’t affect hikers planning trips along the valley to the toe of the Kaskawulsh Glacier. “We’re not really anticipating any changes at this point,” she said.
But she did say those planning canoe or rafting trips down the Alsek River should check with Parks Canada to inquire about higher water levels.
Looking ahead, it’s possible this is the start of something new. The Slims River could remain a dusty valley with a little water trickling through it. Water levels in Kluane Lake could drop by a few metres. Kluane River, the only outflow from the lake, could dwindle as well.
But it’s also possible that something else will shift, and everything will be back to normal next year.
Then again, maybe “normal” isn’t the right word. In the world of glaciers, nothing ever really stands still.
“I think it’s a bit too early right now to be sure about what’s going to happen,” Copland said. “Ultimately, we don’t really know. Nature decides, in the end.”
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