First Example Of Climate-Induced "River Piracy" In Modern Times Uncovered By Scientists

An aerial photograph showing how the meltwater from the Kaskawulsh Glacier (top left) is being diverted away from the Slims Lake (top right) and into the new southwards channel in the center of the image. Dan Shugar/University of Washington Tacoma

Watch out, wanderers of the wilderness – there’s a river pirate about. An entire Alaskan river has walked the proverbial plank and disappeared, and where there was once three closely flowing rivers, there is now only two.

As reported in a brand new study for Nature Geoscience, the Slims River in Canada – which had been flowing out northwards to the Bering Sea for the last 300 years – has abruptly changed course and is now flowing south towards the Gulf of Alaska via the Alsek and Kaskawulsh Rivers.

Technically known as “river piracy,” there are only a few ways in which a river can be completely diverted into flowing into another.

Huge earthquakes, for example, can alter the regional topography to such an extreme extent that one river dramatically changes direction and drains into another. Piracy can also be induced if a landslide blocks the flow of a river. If a quake causes a tree to collapse and form a dam, it’s known as the Shiver Me Timbers phenomenon (disclaimer: This is untrue, but it shouldn’t be).

Plenty of ancient examples of this can be seen in the geological record, but it’s never been observed or documented in modern times. This contemporary case would be the first, and the culprit this time around was actually man-made climate change.

Sentinel-2 satellite imagery shows the dramatic drop in the Slims River flow, and the receding of the Kaskawulsh Glacier (bottom of both images). ESA

Back in the summer of 2016, a team of researchers led by the University of Washington Tacoma visited the Slims River to find that it had all-but-stopped flowing. In fact, they could actively watch it dry up as they stood next to it. Within just four days, it had slipped off this mortal coil.

Using a drone to create 3D elevation models of the landscape, their “postmortem” examination revealed that it was all linked to the Kaskawulsh Glacier.

Meltwater from this vast chunk of ice fueled the Slims River in a northerly direction, but in 2016, an unusually warm spring and summer caused so much melting that it flooded backwards, sending water into the Kaskawulsh River to the east, and another river, the Alsek, to the south.

The Slims River flow was primarily pirated by the Alsek River, which is now up to 70 times larger in size than the extinct former stream. Based on a careful statistical analysis, the team concluded that there’s a 99.5 percent chance that this sudden spike in melting occurred due to anthropogenic climate change.

“The event is a bit idiosyncratic, given the peculiar geographic situation in which it happened,” co-author Professor John Clague, who holds the Chair in Natural Hazard Research at Simon Fraser University, noted in a statement. “In a broader sense, it highlights the huge changes that glaciers are undergoing around the world due to climate change.”

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