Massive ancient lake across the prairies emptied quickly enough to trigger an ice age, study finds

A flood of epic proportions drained at a rate of more than 800 Olympic-size swimming pools per second a glacial lake that stretched across the Prairie provinces more than 12,000 years ago, according to a study by the University of the Alberta.

The discovery supports a theory that the event may have propelled global warming into an ice age.

Geologists have long known of an ancient lake, Glacial Lake Agassiz, which occupied up to 1.5 million square kilometers of what is now southern Manitoba and central Saskatchewan, to the border of Alberta. The lake was formed when the three-kilometer-thick Laurentian Ice Shield at the top of the northern half of North America began to melt about 16,000 years ago, creating a dam that kept the waters out. potential melt to head towards Hudson Bay.

Geomorphological evidence from northern Alberta also suggests that at one point this lake suddenly flowed northwest along a major channel called the Clearwater-Athabasca Spillway, through what is now Fort McMurray, Alta. In the Mackenzie River Basin en route to the Arctic Ocean.

The international study led by Sophie Norris, a former U of A doctoral student studying at the Faculty of Science, examined the amount of water discharged from the meltwater channel.

“We know that a significant discharge passed through the area, but the rate of discharge or the magnitude was pretty much unknown,” said Norris, who is now a postdoctoral researcher at Dalhousie University.

The first part of the study used sedimentary evidence to estimate the force of the water, as well as more than 100 cross-sections of valleys to estimate the size of the flows. The team also created a gradual dam failure model using the erodability of the bedrock of the area and the size of the lake needed for a spillway in the upper Clearwater River.

The team estimated an estimated discharge rate of two million cubic meters of water per second at its height. This volume is about 10 times the average flow of the Amazon River every second and one of the largest known floods on Earth. In total, the flood drained about 21,000 cubic kilometers of water, the equivalent of what is in the Great Lakes, in less than nine months.

“What I find deeply satisfying is that modern hydraulic modeling, when applied to evidence preserved in the landscape, shows how phenomenal flooding spread 12,000 years ago,” said Paul Carling. , co-author of the study from the University of Southampton, UK. “When all the uncertainties are taken into account, the result remains quite solid.”

Another co-author of the article, Daniel Garcia-Castellanos of Geosciences Barcelona in Spain, added that the results of the study suggest that the event was the largest land flood on record following a lake overflow. “It also suggests that we are moving closer to a quantitative understanding of these rapid erosion and flooding events and linking them to long-term erosion of landscapes.”

Additionally, the time period in which this great flood occurred corresponds to an event known as the Younger Dryas, when just as the northern hemisphere was emerging from the Ice Age, it suddenly reverted to near-glacial conditions.

“During the Upper Pleistocene, temperatures returned to normal, when the Earth returned to an ice age,” said Duane Froese, Ph.D. of Norris. supervisor and holder of the Canada Research Chair in Northern Environmental Change at the Department of Earth and Atmospheric Sciences.

“We don’t know for sure that the flood caused the Earth to fall back into the Ice Age, but certainly if you put that much water in the Arctic Ocean, the models show that you get a cooling of the hemisphere’s climate. North.”

Norris said the next steps are to better understand whether this catastrophic discharge occurred at the onset of the cold reversal, in which case it may have been the cause, or just played a part in a series of more complex events.

Norris said Alberta could owe some of its resource wealth to this great flood.

“The oil sands region is mostly in the channel formed by this flooding,” she said. “There would have been a tremendous amount of Quaternary material on top of that, as there is around it, but it was exposed in Fort McMurray by this huge event.”

The article, “Catastrophic Drainage of the Northwestern Outlet of Glacial Lake Agassiz During the Younger Dryas,” was published in Geophysical research letters.