Receding glaciers causing river piracy

Context

As glaciers around the world recede rapidly owing to global warming, some communities are facing a new problem: the sudden disappearance of their rivers.

What is River Piracy?

• River piracy, or stream capture, is a phenomenon of water from one river is diverted into another because of erosion or, in this case, glacier melt.
• Under this the land that has been continuously covered by ice for many centuries will become ice-free, thus redirecting rivers in high mountain areas.
• First case: The first known case of river piracyin modern times was documented in 2016 in Canada’s Yukon Territory.
• Canada’s largest glacier melted so quickly it diverted a large river, and thus significantly reduced the water level of a lake it fed.
• For hundreds of years, the Slims River, or Ä’äy Chù, carried meltwater northwards from the vast Kaskawulsh glacier into the Kluane river then into the Yukon River towards the Bering Sea.
• But in spring 2016, a period of intense melting of the glacier permanently redirected the meltwater of the Ä’äy Chù towards a steeper gradient east via the Kaskawulsh River, into the Gulf of Alaska thousands of miles from its original destination.
• Impact: In most instances, the redirection will be inconsequential. But in some areas with various user groups that rely on the river’s flow, the changes might have a more significant impact.
• It impacts the livelihood of indigenous people.
• It also impacts the flora and fauna of the local area.
  

The new river piracy case

• A rapidly retreating glacier within Glacier Bay national park and reserve in Alaska is expected to change the course of a mighty river it feeds.
• The Grand Plateau glacier in southern Alaska is about 350 metres thick at its tongue, and has long served as a barrier for the Alsek River.
  
• The waterway originates in the St Elias mountain range in Canadaand flows south into Alaska, entering the Pacific Ocean in a channel that flows through Dry Bay, an area known for fishing and rafting.
• Expected change: Over the next three decades the Alsek will abandon its current channel at Dry Bay in favour of a steeper outlet 17 miles (28km) south-east, a pathway freed by the Grand Plateau glacier, which is thinning at a rate of up to 10metres each year.