Ancient lake flood spanned the prairies
• An epic glacial lake flood spanning Canada’s prairies may have been swift enough to trigger the ice age roughly 12,000 years ago, shows research led by the University of Alberta.
The flood from the 1.5-million-square-km Glacial Lake Agassiz drained at more than 800 Olympic swimming pools a second, a finding that supports the theory that it may have propelled the warming Earth back into an ice age, said a recent U of A news release.
Sophie Norris, a former U of A Faculty of Science PHD student, led the study to determine how much water was discharged through the meltwater channel from the lake spanning what is now southern Manitoba and central Saskatchewan.
When the three-kilometre-thick Laurentide Ice Shield atop North America started to melt about 16,000 years ago, the lake formed, say researchers. But the lake eventually spilled out to the northwest, along the major channel known as the Clearwater-athabasca Spillway, through what is now Fort Mcmurray, into the Mackenzie River basin en route to the Arctic Ocean.
“We know that a large discharge has gone through the area but the rate of the discharge or the magnitude was pretty much unknown,” said Norris, now a postdoctoral research fellow at Dalhousie.
Norris added Alberta might owe part of its resource wealth to the great flood. “The oilsands region is essentially within the channel that this flood formed,” she said. “There would have been a huge amount of quaternary material on top of that, as there is in the surrounding area, but it has been exposed in Fort Mcmurray by this huge event.”
The first part of her international study used sedimentary evidence to estimate the flood water’s force, as well as more than 100 valley cross-sections to estimate flow sizes. The research team created a model of gradual dam failure, then determined an estimated discharge rate, at its height, of two million metres cubed of water every second. That means the flood drained about 21,000 cubic kilometres of water — or the amount of water contained in the Great Lakes — in less than nine months.
The time of the flood also corresponds to an event known as the Younger Dryas, when just as the northern hemisphere was coming out of the ice age, it suddenly returned to near-glacial conditions. “During the Late Pleistocene, temperatures were returning to normal, when the Earth slipped back into an ice age,” added Duane Froese, Norris’s PHD supervisor and Canada Research Chair in Northern Environmental Change in the Department of Earth and Atmospheric Sciences.
“We don’t know for sure that the flood caused the Earth to slip back into the ice age, but certainly if you put that much water into the Arctic Ocean, the models show you get cooling of the northern hemisphere climate.”