DEFINITION OF MISSISSIPPI RIVER

The largest river system in the United

States, the Mississippi stretches 2,350 miles (3,780 km) from

northern Minnesota to the end of the Mississippi delta in

Louisiana. The Missouri River is longer than the Mississippi

but carries less water, and the two systems merge at St. Louis,

Missouri, continuing as a larger Mississippi System. Together,

the two rivers have a total length (from the Missouri headwaters

to the mouth of the Mississippi) of 3,740 miles (6,020

km) and drain 1,231,000 square miles (3,188,290 km2)

including parts of 31 states and two Canadian provinces. The

area covered by the basin is about 40 percent of the United

States, or about 13 percent of North America. This combined

system ranks as the world’s third longest river system, after

the Nile and the Amazon. A sediment-free passage is maintained

in the river for navigation all the way from the South

Pass area in the delta to St. Anthony Falls in Minneapolis,

Minnesota. This passage in the river is extensively used for

shipping, making the Mississippi a major economic waterway.

The Mississippi is connected with the Intercoastal

Waterway in the south, and the Great Lakes–St. Lawrence

Seaway in the north through the Illinois Waterway, allowing

commerce to move from Canada to the Gulf of Mexico. The

name Mississippi is derived from an Ojibwa (Chippewa) Indian

word meaning “great river of gathering of waters.”

The source of the Mississippi is in small streams that

feed into Lake Itasca in northern Minnesota. From there it

flows south until it meets the Missouri north of St. Louis,

causing the river to expand to a width of 3,500 feet (1,070

m), and then expands to 4,500 feet (1,375 m) at Cairo, Illinois,

where the Ohio River joins the flow. South of Cape

Girardeau, Missouri, the river begins to meander in large

loops as the gradient decreases on a broad alluvial plain,

which continues through to the delta section that begins in

Mississippi and continues through Louisiana and out into the

Gulf of Mexico. The delta of the Mississippi is a bird’s foot

type of delta, characterized by channels that shift every few

hundred years causing a new lobe to be deposited while the

once-active lobe generally subsides below sea level. Presently,

the active delta lobe that extends past New Orleans to Venice

is overextended, and the river has attempted to change courses

to follow the distributary Atchafalaya River that provides

a much shorter route to the Gulf. The U.S. Army Corps of

Engineers has done everything possible to prevent such a

change, as it would be disastrous for the economies of New

Orleans (which would subside further below sea level) and

the entire United States.

Hernando de Soto of Spain is thought to have been the

first European to discover and explore the Mississippi in

1541, although in 1682 Sieur de La Salle traveled down the

length of the river and claimed the entire territory for France.

After the territory changed hands several times, the United

States acquired the territory as part of the Louisiana Purchase

in 1803. The river soon became the main trade and commerce

route for the new territories in the United States, with

the first steamboat moving up the river in 1811. During the

Civil War the river became a major invasion route from north

to south and was the scene of many major battles, including

the capture of New Orleans by Union forces in 1863. With

the construction of railroads, much of the river’s commerce

was shifted to overland routes. However, the river continues

to be used for shipping bulky freight such as petroleum, sand

and gravel, coal, chemical products, and limestone.

The Mississippi River is divided into three main segments

including the headwaters, the Upper Mississippi River,

and Lower Mississippi River. The headwaters stretch from

the source in Lake Itasca to St. Anthony Falls in Minneapolis

and are characterized by the steepest gradients, including a

drop in elevation from 1,443 feet (440 m) at Lake Itasca to

669 feet (204 m) at St. Anthony Falls, along a distance of 492

miles (794 km). The headwaters flow through thick spruce

forests, swamps, wild rice beds, cattail marshes, natural

lakes, rapids, and glacial deposits. Water in the headwaters is

stained a reddish brown color by organic acids leached from

decaying bog vegetation.

The Upper Mississippi River flows 906 miles (1,462 km)

from St. Anthony Falls to the mouth of the Ohio River at

Cairo, Illinois. The river follows a glacial valley scoured out

during melting of the Wisconsin glaciation starting about

15,000 years ago, and these glaciers and meltwater streams

followed older tectonic features. Water that spilled out of

glacial Lake Agassiz and Lake Duluth (now Lake Superior)

for 2,700 years provided huge amounts of water to the Upper

Mississippi through the Minnesota River Valley, and this

meltwater carved out a river valley to the bedrock that was

300 feet (90 m) deep. By the time the glaciers had retreated

into Canada by 9,200 years ago, the torrents of meltwater

had scoured the Upper Mississippi River basin to depths of

820 feet (250 m) deep, attesting to the strength of the meltwater

floods. Since then the Upper Mississippi basin has been

filling in with glacial outwash, a process that is continuing to

the present day.

The Lower Mississippi River begins at Cairo, Illinois,

where the river enters the gently sloping lowlands of the

Lower Mississippi alluvial valley that continues all the way to

the Gulf of Mexico. Meandering channels on flat to gently

sloping floodplains with low river terraces characterize this

section of the Mississippi. The river is silt laden, as are many

of its main tributaries including the Black River, Tensas River,

Yazoo, Big Sunflower, White, and St. Francis Rivers. There

are many oxbow lakes and abandoned meander channels,

and tributaries that are trapped by former Mississippi River

embayments (Yazoo type rivers) and flow parallel to the main

river for many miles before joining the Mississippi. Hardwood

forests and swamps cover much of the area that has

not been cleared for agriculture. Near New Orleans the river

narrows to about 3,300 feet (1 km) and is about 200 feet (60

m) deep. Beyond New Orleans the river flows on the modern

Mississippi bird’s foot delta, and the river breaks into numerous,

levee-bounded distributary channels that are only slightly

above sea level.

See also DELTAS; FLOOD.

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