Research press release


Nature Geoscience

River piracy following global-warming-induced glacier retreat



Daniel Shugarたちは、ドローンやヘリコプターで得られた画像を人工衛星データおよび河川水位計の放出量データと共に用いて、カナダ・ユーコン地方のカスカウォルシュ氷河の排水を再現した。Shugarたちは、2016年の春に氷河表面で起きた異常な融解が、以前の後退により活動的な氷河から分離して残った氷を越えて、氷の壁を持つ峡谷が発達するのを引き起こしたことを発見した。このことによって、Shugarたちは、シムス川からの最終的にはベーリング海に排出していた氷河の融解水が、太平洋に流れ出ているアルセク川へと流路を変えたことを示している。またShugarたちは、氷河の後退の原因を調べ、気候変動が圧倒的にその原因となり得ると考えている。

同時掲載のNews & Views記事で、Rachel Headleyは、この研究は「氷河の後退と融解による河川争奪という、気候変動の類いまれな影響を捉えている」と述べている。

Meltwater from one of Canada’s largest glaciers has been rerouted from draining northward into the Bering Sea to discharging southward into the Pacific Ocean, due to retreat of the glacier, reports a paper published online this week in Nature Geoscience. The so-called river piracy event is unique during the observational record, and the study concludes that the river rerouting was most likely caused by climate change.

River piracy events - rerouting of rivers through a different drainage basin - can have significant impacts on landscape evolution, ecosystems, water supply and hydroelectric power generation. These events have been documented in the geological record, and are believed to have occurred when the large ice sheets of the Last Glacial Maximum began to decay around 18,000 years ago. However, the impact of modern climate warming on river drainage networks has so far not been documented.

Daniel Shugar and colleagues use imagery obtained by drones and helicopters, along with satellite data and discharge data from river gauges, to reconstruct the drainage of Kaskawulsh Glacier in Yukon, Canada. They find that unusual surface melt on the glacier in spring 2016 led to the development of an ice-walled canyon across remnant ice that had become separated from the active glacier by earlier retreat. They show this rerouted the glacier’s meltwater from Sims River, which ultimately drains into the Bering Sea, to Alsek river, which drains into the Pacific Ocean. The authors then investigate the causes for the glacier retreat and attribute it with overwhelming likelihood to climate change.

In an accompanying News & Views, Rachel Headley writes that the study has “captured a unique impact of climate change: river piracy due to retreating and melting glaciers.”

doi: 10.1038/ngeo2932


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