‘River piracy’ on a high glacier lets one waterway rob another

Channel formed by melting ice diverts water flow, leaving loser high and dry

Kluane Lake

HIGH-WATER ROBBERY  The melting of Kaskawulsh Glacier in northwestern Canada diverted water flow from one river into another, plummeting water levels in the waterway that once fed Kluane Lake (shown). 

Jim Best/University of Illinois

River piracy
RIV-er PAHY-ruh-see n.

The diversion of headwaters from one stream into another

Ahoy! There be liquid booty on the move in the high mountains. Since May 2016, a channel carved through one of northwestern Canada’s largest glaciers has allowed one river to pillage water from another, new observations reveal. This phenomenon, almost certainly the result of climate change, is the first modern record of river piracy caused by a melting glacier, researchers report online April 17 in Nature Geoscience. Such piracy was rampant as the colossal ice sheets of the Last Glacial Maximum began shrinking around 18,000 years ago.

For hundreds of years, the Kaskawulsh Glacier formed a wall that segregates snow and ice meltwater into two streams: the Slims River, which joins with other streams and crosses Alaska before draining into the Bering Sea, and the Kaskawulsh River, which flows southward into the Pacific Ocean.

Last summer, geomorphologist Daniel Shugar of the University of Washington Tacoma and colleagues discovered that melting had carved a canyon across the toe of Kaskawulsh Glacier. This new channel diverts almost all meltwater into the Kaskawulsh River. That’s robbed the now largely parched Slims River and could decrease fish populations and the availability of nutrients downstream, the researchers predict.

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