After the Ice Age: The Return of Life to Glaciated North America by Pielou E. C

Author:Pielou, E. C.
Language: eng
Format: epub
Publisher: The University of Chicago Press

One of the big readvances of the ice in the Great Lakes region happened around 13k B.P., during what is known as the Port Huron stade.15 (A stade is a cold spell within a glaciation; the relatively mild spell between two stades is an interstade.) To call the period a stade is to imply that the readvance was due to climatic cooling. Other evidence, however, suggests a surge of ice. The surge split into four lobes that flowed into the almost ice-free basins of Lakes Superior, Michigan, Huron, and Erie-Ontario, respectively, while ice to east and west of the lobes continued its retreat. This certainly suggests surging, as does the lobes’ speed of flow. They advanced at about two kilometers per year, which is very fast compared with the rate of advance of the margin of a growing ice sheet.

The absence of paleoecological evidence for climatic cooling does not necessarily mean there was no cooling, since ecological inertia could have damped the vegetation’s response. Even so, it makes the surge theory that much more likely. Where the surging ice advanced over forested land, it must have crushed the full-grown forest ahead of it. And when the surging stopped, and the ice cliffs melted back, it would have been forest, rather than tundra, that repossessed the land.

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