When scientists from the University of Illinois and Canada's Simon Fraser University headed to northern Canada last August to do some fieldwork along the Slims River, they were met by a surprising sight. The Yukon river was no longer flowing and instead resembled a "long, skinny lake," researcher Daniel Shugar says, per Phys.org. The reason, as they now explain in a study published in the Nature Geoscience journal: The waterway had become a victim of "river piracy," in this case caused by the retreat of the Kaskawulsh Glacier, which in turn caused the meltwater to completely change its northward course toward the Bering Sea (via the Slims, then Kluane Lake and the Yukon River) and instead merge with the Kaskawulsh River, which flows south to the Gulf of Alaska—and what the Guardian calls the "abrupt" vanishing of the Slims seems to have happened over just four days last spring.
Those four days—May 26 to May 29—showed a sudden drop in the Slims' flow, with Shugar saying comparable river piracy hasn't, to his knowledge, been seen in our lifetimes. The glacier is said to have retreated nearly 2,300 feet in the 50-year period between 1956 and 2007, and in 2016, the rapid pace of the meltwater's movement created an ice channel that directed more water toward the Kaskawulsh River, a tributary of the Alsek River that dumps into the gulf. The glacier's decline is being blamed with 99.5% probability on climate change, and scientists say the new development will affect local wildlife, fish populations, and water chemistry, among other things. "I always point out to climate-change skeptics that Earth's glaciers are becoming markedly smaller, and that can only happen in a warming climate," co-author John Clague says, per Phys.org. (Breathtaking photos show glacier melt.)