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; its outflow breached the U-shaped Big Stone Moraine at Traverse Gap and became the source of River Warren. At the extreme right, the northernmost Oxbow Loop is the Mississippi at downtown Saint Paul . Just to its west and almost invisible is the valley of the Mississippi above its confluence with River Warren at Fort Snelling .]] . The wide channel of River Warren enters from the southwest. The Mississippi enters from the north near the left side and the St. Croix enters from the north at the right. The present rivers are grossly Underfit for their valleys; the widening of the Mississippi to the southeast is the Slackwater Pool from Lock And Dam No. 2 .]] Glacial River Warren or '''River Warren''' was a prehistoric river that drained Lake Agassiz in central North America between 11,700 and 9,400 years ago. The enormous outflow from this lake carved a mighty valley now occupied by the much-smaller Minnesota River and the Upper Mississippi River . CREATION Lake Agassiz was formed from the meltwaters of the . Sansome, ''Minnesota Underfoot'', pp. 174-75; Upham, ''The Glacial Lake Agassiz'' , p. 14-17. From the gap issued the Glacial River Warren. From its inception until final abandonment of Agassiz' southern outlet, this stream drained the meltwater of that lake to the Mississippi valley. The drainage was not however continuous, as Lake Agassiz periodically had other outlets. The Laurentide ice sheet retreated and advanced with climatic variations and these changes in ice cover contributed to Isostatic adjustments in the level of the land over which the watercourses ran. These changes in turn uncovered or blocked the lake's other outlets to the sea.Fisher, ''River Warren Boulders'' , p. 351. COURSE While active this turbulent stream cut and eroded a bed up to five miles (8 km) wide and 250 feet (80 m) deep.Sansome, ''Minnesota Underfoot'', pp. 118-19. This has left a valley which starts at Traverse Gap near Browns Valley, Minnesota , goes southeast to Mankato , then turns northeast to the Twin Cities . River Warren was joined by the comparatively small Mississippi at Fort Snelling , from which the valley continues northeast to present-day Saint Paul , where the massive River Warren Falls once graced the landscape. Over 1700 years this waterfall retreated upstream and undercut the Mississippi at the site of Fort Snelling . The falls then split. The Mississippi falls migrated upstream to form Saint Anthony Falls and create Minnehaha Falls in Minneapolis . The River Warren falls receded west in the Minnesota River valley until they reached an older buried river valley about two miles (3 km) west of the confluence, where the falls were extinguished.Waters, ''The Streams and Rivers of Minnesota'', pp. 226-28. From Saint Paul the valley formed by the combined flow of the River Warren and the Mississippi goes southeast to Prescott, Wisconsin , where it is joined by the St. Croix River , itself once the outlet of another Proglacial Lake , Glacial Lake Duluth which occupied the western part of Lake Superior . From its confluence with the St. Croix the valley continues southeast where the border between Minnesota and Wisconsin is now located. River Warren's effects include the creation of bluffs along the valleys of the Minnesota and Mississippi Rivers, and contributed to the formation of Lake Pepin .Ojakangas, ''Minnesota's Geology'', pp. 110-114. END By about 9400 BP, the ice sheet finally retreated sufficiently far to the north that Lake Agassiz permanently took another outlet and receded below the level of Traverse Gap. River Warren then ceased to run.Fisher, ''River Warren boulders'' , p. 350. The Lake Agassiz area Watershed now feeds the Red River Of The North which flows north, ultimately to Hudson Bay . River Warren's upper valley in the Traverse Gap is now occupied by the tiny Little Minnesota River , which flows into Big Stone Lake and the Minnesota River, which follows the greater river's ancient bed to its confluence with the Mississippi River. These streams occupy only a small cross-section of River Warren's riverbed. ''Valley Formation'' . NAME The hydrology of the oversized valley was first explained by General G. K. Warren in 1868. He made a detailed survey of the valley in his search for possible transcontinental railroad routes. Gouverneur Kemble Warren Papers, 1848-1882 Posthumously, in appreciation of this work, the glacial river that was the outlet of Lake Agassiz was named River Warren.Upham, ''The Glacial Lake Agassiz'' , pp. 7-8. SEE ALSO
REFERENCES Notes Sources Books, journals and monographs
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