As the last ice age waned, a great lake was born.During the final millennia of the last ice age, what was briefly the world's largest lake sat along the southwestern edge of the ice sheet that smothered smoth·er v. smoth·ered, smoth·er·ing, smoth·ers v.tr. 1. a. To suffocate (another). b. To deprive (a fire) of the oxygen necessary for combustion. 2. eastern Canada Eastern Canada (also the Eastern provinces) is the region of Canada generally considered to be east of Manitoba, consisting of the following provinces:
At one point, Canada's Lake Agassiz contained about 30 percent more water than all freshwater bodies of the world hold today (SN: 11/2/02, p. 283). Numerous studies have suggested that the lake disappeared about 8,400 years ago, when the center of the Laurentide Ice Sheet Laurentide Ice Sheet Principal glacial cover of North America during the Pleistocene epoch (1.8 million–10,000 years ago). At its maximum extent it spread as far south as latitude 37° N and covered an area of more than 5 million sq mi (13 million sq km). collapsed into Hudson Bay, allowing the lake to drain into the ocean. Despite widespread agreement on the timing of Lake Agassiz' demise, researchers hadn't pinned down when the lake originated, says Kenneth Lepper, a geoscientist at North Dakota State University North Dakota State University, at Fargo; land-grant and state supported; coeducational; chartered and opened 1890 as North Dakota Agricultural College, achieved university status in 1960. in Fargo. He and his colleagues carbon-dated samples of wood retrieved from sediments in lakes that had formed atop the rocky debris, or moraine moraine (mərān`), a formation composed of unsorted and unbedded rock and soil debris called till, which was deposited by a glacier. The till that falls on the sides of a valley glacier from the bounding cliffs makes up lateral moraines, , that had been pushed south by the advancing ice sheet. Those dates are clustered around 13,950 years ago, the team reports in the July Geology. That's the time when the Laurentide Ice Sheet began to melt and retreat from northern portions of the Great Plains, the team suggests. The nascent Lake Agassiz accumulated between the retreating ice sheet and the moraine, says Lepper. |
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