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Laurentide Ice sheet, glacial lake Agassiz-Ojibway

The Big Flood that Cooled the Earth



From the outset, let’s just make it clear; this has nothing to do with Noah, fig branches or doves. What we’re discussing here is just how it was that the glacial lake Agassiz-Ojibway managed to break its way through to open sea-water and cause a mini ice-age for Europe.

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North America in the geological past is a topic that I am deeply attached too. To consider, in this instance, that between c. 95,000 and c. 20,000 years before the present day North America was covered by a massive ice-sheet is staggering to me. The Laurentide Ice Sheet once covered most of Canada and a vast majority of the northern United States. It went as far south as New York City and Chicago, and then quite precisely – and thus suggestively – followed the course of the Missouri River up to the northern slopes of the Cypress Hills. Beyond that, it merged with the Cordilleran Ice Sheet. That’s all good and well, but what does all of this have to do with cooling the Earth? Well, apart from the fact we’re talking about a massive sheet of ice… Approximately 10,000 years ago the temperature on Earth began to climb steadily higher, forcing the ice in to a quick retreat northward. As it went, it gouged out the hollows that are now the North American Great Lakes. Underneath the surface of the ice began to form a massive freshwater lake, known as Agassiz-Ojibway. It was so vast that it covered parts of Manitoba, Saskatchewan, North Dakota, Ontario and Minnesota. At about 8,200 years ago, Agassiz-Ojibway broke through its barriers and drained in to the North Atlantic, by way of the Hudson Strait and the Labrador Sea. As a result, the North Atlantic Gulfstream –which carries warm water across the North Atlantic to the western shores of Europe, thus causing a measure of warming in the atmosphere – was halted. This subsequently dropped the temperature in Europe, and created what is now known as the Younger Dryas, or the Big Freeze. All of this we know as almost certain fact (as close to fact as we ever get in science these days). What we don’t know is why or how this happened. It is at this point that new research from Quebec researchers Patrick Lajeunesse and Guillaume Saint-Onge comes in to play. Together, the pair criss-crossed Hudson Bay on a research vessel, using sonar to scan more than 10,500 kilometres (6,000 miles) to get a picture of the bay floor. What they found in the south of the bay, were lines of deep waves in the sandy bed, stretching further than 900 kilmoeters in length and some 1.7 meters deep. They also found arcs that had been chiseled as deep as 3 meters in to the sea bed, and found at depths of 80 and 205 meters. Together, according to the duo, these things suggest that at the time of the drainage, the area was still covered by the Laurentide Ice Sheet. The lines in the sand suggested that the bay’s floor had been protected by a lid of ice, and thus caused a sweep of current many to wash over the seabed. As for the chiseled marks in the south of the bay, they believe that icebergs were swept through by the massive current. Trapped in the seabed, the icebergs point acted like a pivot, creating the indentations in the ground. "Laurentide ice was lifted buoyantly, enabling the flood to traverse southern Hudson Bay under the ice sheet," the study suggests. Why may still be a mystery, but we’ll wait on the verdict as to whether we have a how! Joshua Hill, a Geek’s-Geek from Melbourne, Australia, Josh is an aspiring author with dreams of publishing his epic fantasy, currently in the works, sometime in the next 5 years. A techie, nerd, sci-fi nut and bookworm.

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