ined Lake Duluth, a glacial lake that covered the western
Lake Superior basin, joined the River Warren about 30 miles downstream from the present
confluence of the Mississippi and Minnesota Rivers. In Wisconsin, another glacial lake
drained first into what is now the Black River and later the Wisconsin River, both of
which emptied into the River Warren. During the 3,000 years that River Warren carried
water from these and other smaller glacial lakes, the Mississippi River valley was carved
bluff to bluff and the resulting valley was approximately 250 feet deeper than it is
However, there is also
evidence that the main valley is much older than the River Warren and underwent several
cycles of cutting and filling during the Great Ice Age. Even though the Coulee country
escaped the land-leveling effect of the ice mass, the glaciers left their mark by carving
the spectacular Mississippi River that cuts through the heart of this area with the
torrents of water draining from the melting ice mass.
With the demise of the glacial lakes, the tremendous flow of water was diminished and
the Mississippi River became the most important stream in the area. The many tributaries
continued to bring in sand and gravel (sediment) into the wide deep valley of the
Mississippi that the river could no longer carry away. Consequently, the sediment began to
fill in the recently scoured river valley. At each point where major tributaries joined
the Mississippi River, natural sediment dams eventually built up to pond the upstream
portion of the river, forming a natural river lake. The largest
is Lake Pepin which at one
time extended all the way up to St. Paul.
Read more about
the effects of the Ice Age on the Mississippi River and the people who live
along it today! The New Madrid Earthquake, the effects of flooding since the
construction of Locks and Dams, stats on the floods of 1993 and others... and
more... are included in DISCOVER! America's Great River Road, an indispensable
4-Volume guide to "life along the Mississippi River."
Save $10 when you purchase all four
volumes! $62 rather than $72!
To man, a hundred years is a long time; however, that perspective changes when one
realizes that the Upper Mississippi River as we know it has been in existence for 10,000
years. Knowledge of the past can help us to better understand and appreciate the present
day Mississippi River.
This is part of an ongoing series about the plants,
fish, wildlife and issues pertaining to the Mississippi River. For questions or comments,
write to: DNR Office, La Crosse, WI 54601
According to some scholars, catastrophic walls of ice broke off from the
glaciers and joined a massive run-off of melt-water, scouring out the contours of the
Mississippi River. It is envisioned that a sudden collapse of the NA ice cap produced a
massive sea-level rise with the speed of a tidal wave around the world. It is likely that
the river valley in the upper Mississippi was once 500 feet deeper than it is now, filled
as it is with gravel and sand deposited by that melt-water. The accumulated Gulf of Mexico
organisms have provided compelling evidence of a vast flood of fresh water about 11,600
Mark recently sent to us the scholarly results of his investigation into the formation
of the Mississippi River Valley: "The present lower Mississippi River Valley is underlain by an aulacogen, that is,
a rift that developed perpendicular to the larger Gulf of Mexico rift. Occasionally
earthquakes reflect continuing movement along its marginal faults, including the most
severe one in United States hiistory, at New Madrid, Missouri, in 1811-1812" (Dott
and Batten, 1988)..
This triple juction (triple junctions form at the location where supercontinents break
up forming aulacogens) may have formed sometime during the Jurrassic Period as North and
South America began separating (Dott and Batten, 1988). According to Liang (1991), major
rivers are often located at the site of a failed arm of a triple junction, with massive
deposits of sedimentary rock filling the linear basin along the trend. Therefore the l