Lake Agassiz was an immense lake that existed in north-central North America during the last ice age. It is named for Louis Agassiz, the first scientist to realize it had been created by glaciers acting as dams. Larger than many modern seas, its waters were fresh, not salt. At its greatest extent it covered an area larger than California (see map right) and held more water than is today contained in all the freshwater lakes of the world.
When ice still blocked its outflow to the north, it had a southern outlet through a valley that today lies on the South Dakota-Minnesota border, now occupied by Lake Traverse, which now forms the southernmost extension of the Hudson Bay drainage basin (see map →).
This vast body of water drained and refilled, apparently, several times, but emptied finally and completely about 8,000 years ago, when the melting ice of Hudson Bay gave its waters egress. This event raised world sea levels abruptly 1 to 3 meters. Lakes Manitoba and Winnipeg, are residual catchments, which correspond to regions where the original lake was deepest. Though huge by modern standards, they retain only a small fraction Agassiz's original waters.
|
| |
Lake Agassiz (click to enlarge)
|
|
