Spring Break
Colloquium discusses disappearing lake with U of Toledo Prof.
Stefanie Mullins
Issue date: 11/25/08 Section: News
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Lake Agassiz was located in central Canada thousands of years ago. At one point, it may have covered an area the size of Iraq.
However, Lake Agassiz has discharged water at times into different large bodies of water including the Atlantic and Arctic Oceans, the Gulf of Mexico and the Hudson Bay. The drainage has affected the ocean flow and weather patterns at the end of the last ice age, including slowing down ocean currents.
The water from Lake Agassiz has drained because the ice sheets have melted and either flowed over a drainage divide, such as a large structure of solid ice, or under a drainage divide. If the water was flowing underneath the drainage divide, it caused the lake to drain at a much faster rate. The lake drained to such an extent that it no longer exists as one lake, but as several smaller lakes.
There have been at least four major outlets where the water from Lake Agassiz has flowed into the other bodies of water. Dr. Fisher linked a period when the water flow switched from draining to the Gulf of Mexico to the North Atlantic Ocean to the temperature of the Earth increasing.
Fisher and his team have tested upwards of 30 lakes, experimenting in both the summer and the winter, to get an estimated age and timeline for the draining of Lake Agassiz by radio carbon dating. Lakes were chosen on either side of the ridges that may have bordered the drainage path to try to find out how old the moraine, or the debris the drainage has left behind, is to track the progression of the glacier.
The biggest spillway channel out of Lake Agassiz is known as the Big Stone Moraine; it is the biggest spillway channel and runs through to the Gulf of Mexico. It is the best estimate for the start of the glacial lake. This channel eventually stopped draining because the water level in the lake dropped below the bed of the channel, probably due to the opening of another eastern channel which sped up the drainage.
During the period of time that the eastern channel was open, the water flowed into the Great Lakes, specifically into Lake Superior. Lake Agassiz dropped fifty meters during this time and "we don't know why, because the water didn't go the way we thought it did. We also don't know where the water went," said Fisher.
The newest hypothesis is that the water could have evaporated.
The final Natural Sciences Colloquium of the Fall 2008 semester will be given by Dr. Paul Zitzewitz of the University of Michigan - Dearborn, titled "Why Make Precision Measurements." It will take place in room 1010 of the Science Learning and Research Center at 3:10 p.m on Dec. 5.
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