‘River piracy’
melting waters that cut a canyon through the ice, diverting more water into the Alsek River, which flows to the south into the Pacific, robbing the headwaters to the north. The scientists concluded that the river theft “is likely to be permanent.”
Daniel Shugar, an assistant professor of geoscience at the University of Washington-Tacoma, and colleagues described the phenomenon in a paper recently published in the journal Nature Geoscience.
River piracy has been identified since the 19th century by geologists, and it has generally been associated with events such as tectonic shifts and erosion
occurring thousands or even millions of years ago.
Earlier episodes of glacial retreat left evidence of numerous abandoned river valleys, identified through the geological record. In finding what appears to be the first example of river piracy observed in modern times, Shugar and colleagues used more recent technology, including drones, to survey the landscape and monitor the changes in the water coursing away from the Kaskawulsh Glacier.
The phenomenon is unlikely to occur so dramatically elsewhere, Shugar said in a telephone interview, because the glacier itself was forming a high point in the landscape and serving as a drainage divide for water to flow one way or another. As climate change causes more glaciers to melt, however, he said “we may see differences in the river networks and where rivers decide to go.”
Changes in the flow of rivers can have enormous consequences for the landscape and ecosystems of the affected areas, as well as water supplies. When the shift abruptly reduced water levels in Kluane Lake, the Canadian Broadcasting Corp. reported, it left docks for lakeside vacation cabins — which can be reached only by water — high and dry.
The Slims River basin, now nearly dry, experienced frequent and extensive afternoon dust storms through the spring and summer last year, the paper stated. The impacts of climate change, such as sea level rise or the shrinkage of a major glacier, are generally measured over decades, not months as in this case.
“It’s not something you could see if you were just standing on the beach for a couple of months,” Shugar said.
The researchers concluded that the rerouted flow from the glacier shows that “radical reorganizations of drainage can occur in a geologic instant, although they may also be driven by longer-term climate change.” Or, as a writer for the CBC put it in a story about the phenomenon last year, “It’s a reminder that glaciercaused change is not always glacial-paced.”
The underlying message of the new research is clear, Shugar said: “We may be surprised by what climate change has in store for us — and some of the effects might be much more rapid than we are expecting.”
The Nature Geoscience paper is accompanied by an essay from Rachel M. Headley, an assistant professor of geoscience and glacier expert at the University of Wisconsin-Parkside who has studied river piracies that occurred thousands and even millions of years ago.
“That the authors were able to capture this type of event almost as it was happening is significant in and of itself,” she said in an interview via email.
As for the deeper significance of the incident, she said, “While one remote glacial river changing its course in the Yukon might not seem like a particularly big deal, glacier melt is a source of water for many people, and the sediments and nutrients that glacier rivers carry can influence onshore and offshore ecological environments, as well as agriculture.”
Her article in Nature Geoscience concludes that this “unique impact of climate change” could have broad consequences.
“As the world warms and more glaciers melt, populations dependent upon glacial meltwater should pay special attention to these processes.”
Another glacier expert not involved in the research, Brian Menounos of the University of Northern British Columbia, said that while glaciers have waxed and waned as a result of natural forces over the eons, the new paper and his own research underscore the fact that the recent large-scale retreat of glaciers shows humans and the greenhouse gases they produce are reshaping the planet.
“Clearly, we’re implicated in many of those changes,” he said.