This capture of one river's flow by another, documented in a study led by the University of Washington and published April 17 in Nature Geoscience, is the first known case of 'river piracy' in modern times.

'Geologists have seen river piracy, but nobody to our knowledge has documented it happening in our lifetimes,' said Gerard Roe. 'People had looked at the geological record -- thousands or millions of years ago -- not the 21st century, where it's happening under our noses.'

River piracy, also known as stream capture, can happen due to tectonic motion of Earth's crust, landslides, erosion or, in this case, changes in a glacial dam. The new study documents one of the less-anticipated shifts that can occur in a changing climate.

'For the last 300 years, Slims River flowed out to the Bering Sea, and the smaller Kaskawulsh River flowed to the Gulf of Alaska. What we found was the glacial lake that fed Slims River had actually changed its outlet,' they said. 'A 30-meter (100-foot) canyon had been carved through the terminus of the glacier. Meltwater was flowing through that canyon from one lake into another glacial lake, almost like when you see champagne poured into glasses that are stacked in a pyramid.'