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June '12

Paul Karrow

Climate is supreme! Most of Canada was covered by huge glaciers 20,000 years ago, and they were created in a succession of ice ages over the last 2 million years, as shown by deep sea cores. The climate changes resulted from astronomical changes in the amount of solar radiation. Evidence for past ice ages includes both erosional
effects and deposits. Other effects of glaciations include lowering sea level

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by 300 feet in cold times and raising it 20 feet in warm times, as well as pushing down the crust by more than 1000 feet by the enormous weight of the ice. The varying position of the ice edge led to major changes in drainage patterns as water outlets were closed by ice advances or opened by ice retreats.

The history of the Great Lakes goes back about 15,000 years. Early on, most of the basins were ice-filled and meltwaters escaped to the southwest into the Mississippi River basin, but as the ice retreated, lower outlets were opened and meltwaters escaped eastward to the Atlantic Ocean. Concurrently, as the ice thinned and the weight of the ice lessened, the depressed crust rose toward its original level. Since the ice sheet was thickest in Quebec, the rate and amount of uplift have been greatest to the northeast. Evidence of this crustal tilting continues today, as in the Lake Ontario basin, for example, Kingston is rising one foot per century relative to Hamilton. As the outlet for Lake Ontario is at Kingston, the faster rising, the lake level is rising on the land
 around the basin, fastest at Hamilton. Erie is like Ontario so there too water level is rising on the shore. In contrast, in the Huron basin the outlet is in the south, so water level is dropping on the land as the land rises by crustal tilting.

     Detailed records of Great Lakes water level changes only go back to about 1850, but statistical analyses show cyclic changes with cycles of 8, 11 (sun spot cycle of precipitation), 12, 30, and 80 years. Years of distress from low water levels, alternate with those of high water. The all-time low record was in 1964 and the high in 1986.  Of course, as you know, there are annual changes related to the seasonal changes of winter and summer, with the annual high after spring runoff and the annual low in the fall. Annual variations range about one to two feet. If you don’t like your present water level, just be patient. Low water causes navigation problems and wide beaches, and high water levels cause erosion and narrow beaches.


Special thanks to Paul Karrow for writing this summary of his presentation for Pro Buzz.

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