Madrid, 6 (European Press)
An epic flood 12,000 years ago drained a rate of more than 800 Olympic pools per second from a glacial lake stretching 1.5 million kilometers. Squares in present-day Canada.
The discovery of a University of Alberta study bolsters the theory that the event may have altered global warming, sending it back to the Ice Age.
Geologists have long known of an ancient lake, the Glacial Agassiz, which stretched across what is now southern Manitoba and central Saskatchewan to the Alberta border. The lake formed when the three-kilometre-thick Laurentide Ice Shelf at the top of the northern half of North America began to melt about 16,000 years ago, creating a dam that prevented potential meltwater from reaching the bay from the Hudson.
Geomorphological evidence from northern Alberta also indicates that at some point, that lake suddenly spilled northwestward along a major channel known as the Clearwater-Athabasca Spillway, through what is now Fort McMurray in the Mackenzie River Basin on its way to the Arctic Ocean.
The international study led by Sophie Norris, a former student in the College of Science, looked at the amount of water discharged through the meltwater channel.
“We know that a large discharge has passed through the area, but the rate or magnitude of the discharge was virtually unknown,” Norris, now a postdoctoral researcher at Dalhousie University, said in a statement.
The first part of the study used sedimentary evidence to estimate the strength of the water, as well as more than 100 valley cross-sections to estimate the volume of the flows. The team also created a stepwise model of dam failure using the area’s rock erosion ability and lake size needed for a drainage stream through the upper Clearwater River.
The team obtained an estimated discharge rate of 2 million cubic meters of water per second, at its peak. This volume is nearly 10 times the average Amazon River discharge per second and one of the largest known floods on Earth. In total, the flood drained about 21,000 cubic kilometers of water, roughly equal to what is found in the Great Lakes, in less than nine months.
“What I find very satisfactory is that recent hydraulic modeling, when applied to the evidence preserved in the landscape, shows how the massive flood spread 12,000 years ago,” said Paul Carling, co-author of the study from the University of Southampton, UK. United. “When all the uncertainties are considered, the result remains very strong.”
Another co-author of the article, Daniel García Castellanos of Geociencias Barcelona in Spain, added that the study results indicate that the event was the largest land flood ever recorded due to a lake overflow. “It also indicates that we are getting closer to quantitatively understanding rapid eroding flood events and linking them to long-term landscape erosion.”
Moreover, the period in which this great flood occurred corresponds to an event known as the Young Dryas, when the Northern Hemisphere was emerging from the Ice Age, it suddenly reverted to semi-glacial conditions.
“During the late Pleistocene, temperatures returned to normal as the Earth returned to the Ice Age,” said Duane Froese, PhD supervisor in Norris’ Department of Earth and Atmospheric Sciences.
“We don’t know for sure if the flood caused the Earth to revert to an ice age, but for sure if you put a lot of water in the Arctic Ocean, models show that the climate in the northern hemisphere is cold.”
The next steps, Norris said, are to better understand whether this catastrophic discharge occurred at the start of the cold reversal, in which case it might have been the cause, or simply played a role in a more complex chain of events.
Norris said Alberta could owe some of its wealth of resources to this great flood.
“The oil sands area is mainly located within the channel that formed this flood,” he said. “There was a lot of Quaternary material on top of that, as in the surrounding area, but it was revealed at Fort McMurray by this great event.”
The study was published in Geophysical Research Letters.