Physical geography Mississippi River

1 physical geography

1.1 divisions

1.1.1 upper mississippi
1.1.2 middle mississippi
1.1.3 lower mississippi


1.2 watershed
1.3 outflow
1.4 course changes

1.4.1 prehistoric courses
1.4.2 historic course changes


1.5 new madrid seismic zone

physical geography

the geographical setting of mississippi river includes considerations of course of river itself, watershed, outflow, prehistoric , historic course changes, , possibilities of future course changes. new madrid seismic zone along river noteworthy. these various basic geographical aspects of river in turn underlie human history , present uses of waterway , adjacent lands.

divisions

the mississippi river can divided 3 sections: upper mississippi, river headwaters confluence missouri river; middle mississippi, downriver missouri ohio river; , lower mississippi, flows ohio gulf of mexico.

upper mississippi

the beginning of mississippi river @ lake itasca (2004)



mississippi head of navigation, st. anthony falls



confluence of wisconsin , mississippi rivers, viewed wyalusing state park in wisconsin

the upper mississippi runs headwaters confluence missouri river @ st. louis, missouri. divided 2 sections:

the source of upper mississippi branch traditionally accepted lake itasca, 1,475 feet (450 m) above sea level in itasca state park in clearwater county, minnesota. name itasca chosen designate true head of mississippi river combination of last 4 letters of latin word truth (veritas) , first 2 letters of latin word head (caput). however, lake in turn fed number of smaller streams.

from origin @ lake itasca st. louis, missouri, waterway s flow moderated 43 dams. fourteen of these dams located above minneapolis in headwaters region , serve multiple purposes, including power generation , recreation. remaining 29 dams, beginning in downtown minneapolis, contain locks , constructed improve commercial navigation of upper river. taken whole, these 43 dams shape geography , influence ecology of upper river. beginning below saint paul, minnesota, , continuing throughout upper , lower river, mississippi further controlled thousands of wing dikes moderate river s flow in order maintain open navigation channel , prevent river eroding banks.

the head of navigation on mississippi coon rapids dam in coon rapids, minnesota. before built in 1913, steamboats go upstream far saint cloud, minnesota, depending on river conditions.

the uppermost lock , dam on upper mississippi river upper st. anthony falls lock , dam in minneapolis. above dam, river s elevation 799 feet (244 m). below dam, river s elevation 750 feet (230 m). 49-foot (15 m) drop largest of mississippi river locks , dams. origin of dramatic drop waterfall preserved adjacent lock under apron of concrete. saint anthony falls true waterfall on entire mississippi river. water elevation continues drop steeply passes through gorge carved waterfall.

after completion of st. anthony falls lock , dam in 1963, river s head of navigation moved upstream, coon rapids dam. however, locks closed in 2015 control spread of invasive asian carp, making minneapolis once again site of head of navigation of river.

the upper mississippi has number of natural , artificial lakes, widest point being lake winnibigoshish, near grand rapids, minnesota, on 11 miles (18 km) across. lake onalaska, created lock , dam no. 7, near la crosse, wisconsin, more 4 miles (6.4 km) wide. lake pepin, natural lake formed behind delta of chippewa river of wisconsin enters upper mississippi, more 2 miles (3.2 km) wide.

by time upper mississippi reaches saint paul, minnesota, below lock , dam no. 1, has dropped more half original elevation , 687 feet (209 m) above sea level. st. paul st. louis, missouri, river elevation falls more slowly, , controlled , managed series of pools created 26 locks , dams.

the upper mississippi river joined minnesota river @ fort snelling in twin cities; st. croix river near prescott, wisconsin; cannon river near red wing, minnesota; zumbro river @ wabasha, minnesota; black, la crosse, , root rivers in la crosse, wisconsin; wisconsin river @ prairie du chien, wisconsin; rock river @ quad cities; iowa river near wapello, iowa; skunk river south of burlington, iowa; , des moines river @ keokuk, iowa. other major tributaries of upper mississippi include crow river in minnesota, chippewa river in wisconsin, maquoketa river , wapsipinicon river in iowa, , illinois river in illinois.

the upper mississippi largely multi-thread stream many bars , islands. confluence st. croix river downstream dubuque, iowa, river entrenched, high bedrock bluffs lying on either side. height of these bluffs decreases south of dubuque, though still significant through savanna, illinois. topography contrasts lower mississippi, meandering river in broad, flat area, flowing alongside bluff (as @ vicksburg, mississippi).

the confluence of mississippi (left) , ohio (right) rivers @ cairo, illinois, demarcation between middle , lower mississippi river


middle mississippi

the mississippi river known middle mississippi upper mississippi river s confluence missouri river @ st. louis, missouri, 190 miles (310 km) confluence ohio river @ cairo, illinois.

the middle mississippi relatively free-flowing. st. louis ohio river confluence, middle mississippi falls 220 feet (67 m) on 180 miles (290 km) average rate of 1.2 feet per mile (23 cm/km). @ confluence ohio river, middle mississippi 315 feet (96 m) above sea level. apart missouri , meramec rivers of missouri , kaskaskia river of illinois, no major tributaries enter middle mississippi river.

lower mississippi

lower mississippi river near new orleans

the mississippi river called lower mississippi river confluence ohio river mouth @ gulf of mexico, distance of 1,000 miles (1,600 km). @ confluence of ohio , middle mississippi, long-term mean discharge of ohio @ cairo, illinois 281,500 cubic feet per second (7,970 cubic metres per second), while long-term mean discharge of mississippi @ thebes, illinois (just upriver cairo) 208,200 cu ft/s (5,900 m/s). thus, volume, main branch of mississippi river system @ cairo can considered ohio river (and allegheny river further upstream), rather middle mississippi.

in addition ohio river, major tributaries of lower mississippi river white river, flowing in @ white river national wildlife refuge in east central arkansas; arkansas river, joining mississippi @ arkansas post; big black river in mississippi; , yazoo river, meeting mississippi @ vicksburg, mississippi. widest point of mississippi river in lower mississippi portion exceeds 1 mile (1.6 km) in width in several places.

deliberate water diversion @ old river control structure in louisiana allows atchafalaya river in louisiana major distributary of mississippi river, 30% of mississippi flowing gulf of mexico route, rather continuing down mississippi s current channel past baton rouge , new orleans on longer route gulf. although red river commonly thought tributary, not, because water flows separately gulf of mexico through atchafalaya river.

watershed

map of mississippi river watershed.




an animation of flows along rivers of mississippi watershed.

the mississippi river has world s fourth-largest drainage basin ( watershed or catchment ). basin covers more 1,245,000 square miles (3,220,000 km), including or parts of 31 u.s. states , 2 canadian provinces. drainage basin empties gulf of mexico, part of atlantic ocean. total catchment of mississippi river covers 40% of landmass of continental united states. highest point within watershed highest point of rocky mountains, mount elbert @ 14,440 feet (4,400 m).

sequence of nasa modis images showing outflow of fresh water mississippi (arrows) gulf of mexico (2004)

in united states, mississippi river drains majority of area between crest of rocky mountains , crest of appalachian mountains, except various regions drained hudson bay red river of north; atlantic ocean great lakes , saint lawrence river; , gulf of mexico rio grande, alabama , tombigbee rivers, chattahoochee , appalachicola rivers, , various smaller coastal waterways along gulf.

the mississippi river empties gulf of mexico 100 miles (160 km) downstream new orleans. measurements of length of mississippi lake itasca gulf of mexico vary somewhat, united states geological survey s number 2,320 miles (3,730 km). retention time lake itasca gulf typically 90 days.

outflow

the mississippi river discharges @ annual average rate of between 200 , 700 thousand cubic feet per second (7,000–20,000 m/s). although fifth-largest river in world volume, flow small fraction of output of amazon, moves 7 million cubic feet per second (200,000 m/s) during wet seasons. on average, mississippi has 8% flow of amazon river.

fresh river water flowing mississippi gulf of mexico not mix salt water immediately. images nasa s modis (to right) show large plume of fresh water, appears dark ribbon against lighter-blue surrounding waters. these images demonstrate plume did not mix surrounding sea water immediately. instead, stayed intact flowed through gulf of mexico, straits of florida, , entered gulf stream. mississippi river water rounded tip of florida , traveled southeast coast latitude of georgia before mixing in thoroughly ocean no longer detected modis.

before 1900, mississippi river transported estimated 400 million metric tons of sediment per year interior of united states coastal louisiana , gulf of mexico. during last 2 decades, number 145 million metric tons per year. reduction in sediment transported down mississippi river result of engineering modification of mississippi, missouri, , ohio rivers , tributaries dams, meander cutoffs, river-training structures, , bank revetments , soil erosion control programs in areas drained them.

course changes

over geologic time, mississippi river has experienced numerous large , small changes main course, additions, deletions, , other changes among numerous tributaries, , lower mississippi river has used different pathways main channel gulf of mexico across delta region.

through natural process known avulsion or delta switching, lower mississippi river has shifted final course mouth of gulf of mexico every thousand years or so. occurs because deposits of silt , sediment begin clog channel, raising river s level , causing find steeper, more direct route gulf of mexico. abandoned distributaries diminish in volume , form known bayous. process has, on past 5,000 years, caused coastline of south louisiana advance toward gulf 15 50 miles (24 80 km). active delta lobe called birdfoot delta, after shape, or balize delta, after la balize, louisiana, first french settlement @ mouth of mississippi.

prehistoric courses

the current form of mississippi river basin largely shaped laurentide ice sheet of recent ice age. southernmost extent of enormous glaciation extended present-day united states , mississippi basin. when ice sheet began recede, hundreds of feet of rich sediment deposited, creating flat , fertile landscape of mississippi valley. during melt, giant glacial rivers found drainage paths mississippi watershed, creating such features minnesota river, james river, , milk river valleys. when ice sheet retreated, many of these temporary rivers found paths hudson bay or arctic ocean, leaving mississippi basin many features oversized existing rivers have carved in same time period.

ice sheets during illinoian stage 300,000 132,000 years before present, blocked mississippi near rock island, illinois, diverting present channel farther west, current western border of illinois. hennepin canal follows ancient channel of mississippi downstream rock island hennepin, illinois. south of hennepin, alton, illinois, current illinois river follows ancient channel used mississippi river before illinoian stage.

view along former riverbed @ tennessee/arkansas state line near reverie, tennessee (2007)

timeline of outflow course changes

c.5000 bc: last ice age ended; world sea level became now.
c.2500 bc: bayou teche became main course of mississippi.
c.800 bc: mississippi diverted further east.
c.200 ad: bayou lafourche became main course of mississippi.
c.1000 ad: mississippi s present course took over.
before c.1400 ad: red river of south flowed parallel lower mississippi sea
15th century: turnbull s bend in lower mississippi extended far west captured red river of south. red river below captured section became atchafalaya river.
1831: captain henry m. shreve dug new short course mississippi through neck of turnbull s bend.
1833 november 1873: great raft (a huge logjam in atchafalaya river) cleared. atchafalaya started capture mississippi , become new main lower course.
1963: old river control structure completed, controlling how mississippi water entered atchafalaya.
cahokia s rise , fall linked river flooding (article in popular archaeology periodical)

historic course changes

in march 1876, mississippi changed course near settlement of reverie, tennessee, leaving small part of tipton county, tennessee, attached arkansas , separated rest of tennessee new river channel. since event avulsion, rather effect of incremental erosion , deposition, state line still follows old channel. town of kaskaskia, illinois once stood on peninsula @ confluence of mississippi , kaskaskia (okaw) rivers. founded french colonial community, later became capital of illinois territory , first state capital of illinois until 1819. beginning in 1844, successive flooding caused mississippi river encroach east. major flood in 1881 caused overtake lower 10 miles of kaskaskia river, forming new mississippi channel , cutting off town rest of state. later flooding destroyed of remaining town, including original state house. today, remaining 2,300 acre island , community of 14 residents known enclave of illinois , accessible missouri side.

new madrid seismic zone

the new madrid seismic zone, along mississippi river near new madrid, missouri, between memphis , st. louis, related aulacogen (failed rift) formed @ same time gulf of mexico. area still quite active seismically. 4 great earthquakes in 1811 , 1812, estimated @ approximately 8 on richter magnitude scale, had tremendous local effects in sparsely settled area, , felt in many other places in midwestern , eastern u.s. these earthquakes created reelfoot lake in tennessee altered landscape near river.