page_title: Glacial history of Minnesota
section_title: Glacial Lake Duluth
hierarchical_section_title: Glacial history of Minnesota / Lake formation / Glacial lakes / Glacial Lake Duluth
caption_attribution_description: English: From...
context_page_description: The glacial history of Minnesota is most defined since the onset of the last glacial period, which ended some 10,000 years ago. Within the last million years, most of the Midwestern United States and much of Canada were covered at one time or another with an ice sheet. This continental glacier had a profound effect on the surface features of the area over which it moved. Vast quantities of rock and soil were scraped from the glacial centers to its margins by slowly moving ice and redeposited as drift or till. Much of this drift was dumped into old preglacial river valleys, while some of it was heaped into belts of hills at the margin of the glacier. The chief result of glaciation has been the modification of the preglacial topography by the deposition of drift over the countryside. However, continental glaciers possess great power of erosion and may actually modify the preglacial land surface by scouring and abrading rather than by the deposition of the drift.
  The marks of glaciation vastly altered Minnesota's topography. Probably the most significant change was in the character and extent of the drainage.
context_section_description: Glacial Lake Duluth is the body of water that formed at the southwestern margin of the Superior lobe and occupied a much larger area than the present Lake Superior. Its shorelines stood nearly 148 meters above the level of its modern successor, Lake Superior. During its early history Lake Duluth drained into the Mississippi River down the St. Croix River Valley. There were two outlets, one along the Kettle and Nemadji Rivers in Minnesota and another to the east along the Bois Brule River in Wisconsin. Later, however, when the Superior lobe had retreated farther to the northeast, the waters of Lake Duluth merged with those in the Michigan and Huron basins, and the southern outlets were abandoned in favor of a lower one on the east end of Lake Superior. The Kettle River no longer drains Lake Superior, but resides in a large valley, which itself could not have produced with its present discharge. The Nemadji and Bois Brule Rivers actually flow northward toward Lake Superior through the eastern proglacial outlet. Even though vast amounts of water flowed over the southern rim of Lake Superior, the Bois Brule River outlet was never scoured deep enough to remove a continental divide at the Bois Brule River's headwaters.
caption: Glacial Lake Duluth
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