Proglacial lakes of Minnesota

From Wikipedia, the free encyclopedia

Present-day Minnesota, with proglacial lakes added in dark blue.
Present-day Minnesota, with proglacial lakes added in dark blue.

The proglacial lakes of Minnesota were lakes created in what is now the U.S. state of Minnesota in central North America in the waning years of the last glacial period. As the Laurentide ice sheet decayed at the end of the Wisconsin glaciation, lakes were created in depressions or behind moraines left by the glaciers. Evidence for these lakes is provided by topography and sedimentary deposits characteristic of lakebeds, referred to as lacustrine deposits on glaciolacustrine landscapes.[1] Not all contemporaneous, these glacial lakes drained after the retreat of the lobes of the ice sheets that blocked their outlets, or whose meltwaters fed them. There were a number of large lakes, one of which, Lake Agassiz, was the largest body of freshwater ever known to have existed on the North American continent; there were also dozens of smaller and more transitory lakes filled from glacial meltwater, which shrank or dried as the ice sheet retreated north.

Contents

[edit] Glacial Lake Agassiz

Main article: Glacial Lake Agassiz

Glacial Lake Agassiz was an enormous lake, larger in area than all the Great Lakes combined, and the largest body of fresh water ever to have existed in North America.[2] It extended from its outlet near Browns Valley, Minnesota west into South Dakota and North Dakota and north into Saskatchewan, Manitoba, and Ontario.[3] In Minnesota the lake occupied the Red River Valley in northwestern Minnesota and the western part of the watershed of the Rainy River in the northern part of the state.[4] Its southern outlet was through the Traverse Gap, a spillway channel cut through the Big Stone Moraine by Glacial River Warren,[5] an enormous stream which carved the valley of the Minnesota River as well as that of the Upper Mississippi River below the confluence of those successor streams.[6] Lake Agassiz' present-day remnants include Lake of the Woods and Upper and Lower and Red Lake.[7]

[edit] Glacial Lake Upham

Lake Upham was formed in the wake of the retreat of the St. Louis Sublobe of the Superior Lobe.[8] Its original outlet was through Lake Aitkin and the Mississippi River, but eventually drained via the Saint Louis River.[9] Its lakebed is now a broad boggy area in the watershed of the latter stream and that of its principal tributary the Cloquet River.

[edit] Glacial Lake Aitkin

Lake Aitkin was also a product of the recession of the St. Louis Sublobe.[10] It lay to the southwest of Lake Upham, along the valley of the Mississippi River north of present-day Lake Mille Lacs in central Minnesota. The lakebed is now a low sandy and clayey bottomland along the meanders of the Mississippi.[11]

[edit] Glacial Lake Duluth

Main article: Glacial Lake Duluth

Glacial Lake Duluth is the name given to the largest of a series of named lakes or lake stages occupying parts of the Lake Superior basin. As its current outlet to the east was blocked by the Superior Lobe of the ice sheet, Lake Duluth drained through two outlets which crossed the present St. Lawrence Divide to the valley of the Saint Croix River and the Mississippi. One outlet was a route from the western part of the lake through the Nemadji River basin and down the present Moose and Kettle Rivers; the other was via the modern Bois Brule River to the Saint Croix.[12] At its peak, Lake Duluth was 148 meters higher than Superior's present level.[13] When the glacier retreated the lake was able to drain to the east.

[edit] Glacial Lake Grantsburg

Lake Grantsburg, formed when the Grantsburg Sublobe of the Des Moines Lobe blocked southward drainage of the ice-free land to its north. It extended from St. Cloud east-northeast to Grantsburg, Wisconsin, whence its outflow ran south along the east front of the ice sheet down the valley of the Saint Croix River.[14]

[edit] Glacial Lake Minnesota

Lake Minnesota was a complex of lakes formed by or on the Des Moines Lobe generally south of Mankato, Minnesota. Evidence for it is found in lacustrine sediments in that region.[15] The lakes may have consisted of bodies of water trapped on the surface of the decaying ice sheet,[16] lakes created as the lobe retreated,[17] or depressions filled from the overflow of Glacial River Warren.[18]

[edit] See also

[edit] References

[edit] Notes

  1. ^ Hudak et al., Landscape Suitability Models for Geologically Buried Precontact Cultural Resources, Glossary.
  2. ^ Waters, Streams and Rivers of Minnesota, p. 106.
  3. ^ Waters, Streams and Rivers of Minnesota, p. 106.
  4. ^ Waters, Streams and Rivers of Minnesota, p. 107.
  5. ^ Sansome, Minnesota Underfoot, pp. 177-79.
  6. ^ Ojakangas and Matsch, Minnesota's Geology, pp. 109-110.
  7. ^ Ojakangas and Matsch, Minnesota's Geology, pp. 109.
  8. ^ Ojakangas and Matsch, Minnesota's Geology, p. 109.
  9. ^ Waters, Streams and Rivers of Minnesota, pp. 26, 28-29.
  10. ^ Ojakangas and Matsch, Minnesota's Geology, p. 109.
  11. ^ Sansome, Minnesota Underfoot, p. 155; Waters, Streams and Rivers of Minnesota, pp. 26, 211, 225.
  12. ^ Waters, Streams and Rivers of Minnesota, pp. 28, 147.
  13. ^ Huber, Glacial and Postglacial Geologic History of Isle Royale National Park lists the peak elevation of Lake Duluth at 1085 feet (331 m), which is approximately 485 feet (148 m) higher than Superior's 2007 elevation of 600 feet (183 m). Ojakangas and Matsch list the peak elevation even higher, at 335 m. Minnesota's Geology, p. 110.
  14. ^ Ojakangas and Matsch, Minnesota's Geology, pp. 106-07, 212.
  15. ^ Cooper, Soil Forming Factors.
  16. ^ Ojakangas and Matsch, Minnesota's Geology, p. 226.
  17. ^ Ojakangas and Matsch, Minnesota's Geology, p. 109.
  18. ^ Hudak and Hajic, Landscape Suitability Models for Geologically Buried Precontact Cultural Resources, section 12.3.4.1 (Landscapes: Paleo-Valley Landscape).

[edit] Sources