Scooped from Precambrian and early Paleozoic bedrock by the Pleistocene glaciers, the Great Lake basins of North America have varied subsurface topography. Like the ocean floor, their depth varies dramatically from one region to another.
Lake Superior, largest of the Great Lakes in both volume and surface area, has an average depth of 483 feet and a maximum depth of 1332 feet; the latter is in the east-central part of the lake, just ENE of the tip of the Keweenaw Peninsula. Lake Michigan has an average depth of 279 feet and a maximum depth of 923 feet between the central Door County Peninsula of Wisconsin and Frankfort, Michigan. Lake Huron's average depth is 195 feet and its deepest section (750 feet) is along its eastern edge, just west of Ontario's Bruce Peninsula. Lake Erie is the shallowest of the Great Lakes, having an average depth of only 62 feet; its deepest pool (210 feet) is near its eastern end. Finally, Lake Ontario, while the smallest of the Great Lakes in area, ranks second in average depth (283 feet) and has a maximum depth of 802 feet in its eastern section.
While the basins of the Great Lakes will gradually fill with sediment and may be rearranged when glaciers return to the Upper Midwest, the surface shape and hydrology of the lakes may be altered by another factor. As southern Canada continues to rebound from the weight of the Wisconsin Ice Sheets, the basins are tipping toward the southwest and, eventually, may drain into the Mississippi via the Illinois River corridor.
