ower
Mississippi River Valley was probably formed during the Jurassic period, some 208 million
years ago, as a failed arm of a triple junction.
According to Ojakangas and Matsch (1982) large glacial lakes were formed as the
glaciers retreated--the largest of the glacial lakes, Lake Agassiz, was formed as the Des
Moines Lobe of the glacier retreated some 12,000 years ago and the drainage of this
approximately 320,000 square kilometer lake may be responsible for the formation of the
Upper Mississippi River Valley--the rivers were responsible for draining the large amounts
of water from the melting glaciers. Ojakangas and Matsch indicate that Lake Agassiz
probably drained via the Minnesota River into the present day Mississippi River (1982).
more information: Dott, H.R., R.L. Batten. 1988. _Evolution of the Earth. Fourth Edition._
New York. McGraw-Hill Book Company. p463, 555. Laing, D. 1991. _The Earth System. An
Introduction to Earth Science._ Dubuque, IA. Wm. C. Brown Publishers. p. 134. Ojakangas,
R.W., C.L. Matsch. 1982. _Minnesota's Geology._ Minnesota. University of Minnesota Press.
Another Letter from our expert Readers!
I enjoy your web page. Information provided by Mark
suggesting the Lower Mississippi is millions of years old is a bit misleading.
Until relatively recently (geologically speaking), most of the Mississippi basin
drained northward toward the arctic. The modern Mississippi valley formed during
the ice ages, however subsidence in the embayment area was probably more
important than any role played by ice. Some of drainage shifts that accompanied
this crustal tilting are described by J.S. Aber at this web site: http://www.emporia.edu/earthsci/chert/chert.htm
Drainage patterns feeding sediment into the Gulf of Mexico have evolved
during the ice ages, changing from a pattern of multiple moderate size rivers
(Rio Grande, Sabine/Red, Mississippi, southern Appalachian) to a system
dominated by the modern Mississippi. There is a map which illustrates the
process published in this article: Prather, B. E., Booth, J. R., Steffens, G.
S., and Craig, P. A., 1998, Classification, lithologic calibration, and
stratigraphic succession of seismic facies of intraslope basins, deep-water Gulf
of Mexico: AAPG Bulletin, v. 82, p. 701-720.