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34-542: This plain with its rich alluvial soil , served as the center for the pre-Columbian Cahokia Mounds civilization, and later the French settlement of Illinois Country . Deforestation of the river banks in the 19th century to fuel steamboats had dramatic environmental effects in this region. The Mississippi River between St. Louis and the confluence with the Ohio River became wider and more shallow, as unstable banks collapsed into

68-585: A volcanic " hotspot " in the Earth's mantle (specifically, the Bermuda hotspot ) that was undergoing a period of intense activity. The upwelling of magma from the hotspot forced the further uplift to a height of perhaps 2–3 km of part of the Appalachian-Ouachita range, forming an arch . The uplifted land quickly eroded and, as North America moved away from the hot spot and as the hotspot's activity declined,

102-547: A large bay in the Cretaceous through early Cenozoic shoreline. The New Madrid Seismic Zone lies at the northern end of the embayment. It was the site of the large New Madrid earthquakes of 1811-12. The area is underlain by some anomalous geology. The Reelfoot Rift is an ancient failed continental rift , an aulacogen , which dates back to the Precambrian break-up of the supercontinent Rodinia . The more recent opening of

136-602: A state legal system. The rivers were used as transportation routes for trading and travel. The introduction of steamboats to the Mississippi and other major rivers led to deforestation of the river banks in the 19th century. The steamboats consumed much wood for fuel, leading to dramatic environmental effects along the Mississippi River between St. Louis and the confluence with the Ohio River . With so many trees taken down,

170-402: A stream bed, on a floodplain , in an alluvial fan or beach , or in similar settings. Alluvium is also sometimes called alluvial deposit . Alluvium is typically geologically young and is not consolidated into solid rock. Sediments deposited underwater, in seas, estuaries , lakes, or ponds, are not described as alluvium. Floodplain alluvium can be highly fertile, and supported some of

204-524: Is a topographically low-lying basin that is filled with Cretaceous to recent sediments . The northern end of the embayment appears as an anomalous break in regional geologic structure with Paleozoic sedimentary rocks both to the east in Kentucky and Tennessee and to the west in Missouri and Arkansas . The current sedimentary basin results from the filling of a Cretaceous tectonic basin and existed as

238-610: Is a physiographic feature in the south-central United States , part of the Mississippi Alluvial Plain . It is essentially a northward continuation of the fluvial sediments of the Mississippi River Delta to its confluence with the Ohio River at Cairo, Illinois . The current sedimentary area was formed in the Cretaceous and early Cenozoic by the filling with sediment of a pre-existing basin. An explanation for

272-520: Is often referred to as "cover" because these sediments obscure the underlying bedrock . Most sedimentary material that fills a basin ("basin fill") that is not lithified is typically lumped together as "alluvial". Alluvium of Pliocene age occurs, for example, in parts of Idaho. Alluvium of late Miocene age occurs, for example, in the valley of the San Joaquin River , California. Mississippi River Valley The Mississippi embayment

306-572: The Atlantic Ocean and Gulf of Mexico during late Paleozoic to early Mesozoic break-up of Pangea no doubt affected and may have partially re-activated the old rift. The Mississippi embayment represents a break in what was once a single, continuous mountain range comprising the modern Appalachian range, which runs roughly on a north–south axis along the Atlantic coast of the United States, and

340-564: The Ouachita range, which runs on a rough east–west axis west of the Mississippi River . The ancestral Appalachian-Ouachita range was thrust up when the tectonic plate carrying North America came into contact with the plates carrying South America and Africa when all three became joined in the ancient supercontinent Pangaea about 300 million years ago. As Pangaea began to break up about 200 million years ago, North America passed over

374-645: The 19th century, the term had come to mean recent sediments deposited by rivers on top of older diluvium , which was similar in character but interpreted as sediments deposited by Noah's flood . With the rejection by geologists of the concept of a primordial universal flood, the term "diluvium" fell into disfavor and was replaced with "older alluvium". At the same time, the term "alluvium" came to mean all sediment deposits due to running water on plains. The definition gradually expanded to include deposits in estuaries, coasts, and young rock of marine and fluvial origin. Alluvium and diluvium were grouped as colluvium in

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408-637: The American Bottom. Its maximum width is about 9 miles (14 km) in the north, and it is about 2 to 3 miles in width throughout most of its southern extent. Before European settlement, the area was home to indigenous peoples for many centuries. The peak civilization was created by peoples of the Mississippian culture , known as the Mound Builders . With the cultivation of maize, they were able to create food surpluses and build concentrated settlements in

442-569: The Mississippi River to Illinois imposed a tax on heavy traffic. Rather than pay it, developers simply located their industries in East St. Louis. In the early 20th century, dramatic growth in industrial jobs in the American Bottom attracted many European immigrants and African-American migrants. The latter left the rural South in the Great Migration to work in factories and gain better lives for their children. Eastern European immigrants founded

476-463: The Mississippi shifted, it was cut off from the mainland of Illinois and is connected to Missouri land. The area of the Bottom directly across from St. Louis became highly industrialized. Industrialists located many "smokestack" industries here, such as steel mills, chemical plants, and oil refineries, because they ran on Illinois coal. In addition, the people who built the first bridge from St. Louis across

510-528: The Mississippians, Americans made massive changes in the floodplain; their development has reduced its ability to absorb floods. The destruction of wetlands and paving over of areas along all the major rivers has increased the severity of flooding over the decades, despite attempted engineering solutions for flood control, which in turn have exacerbated flooding. During the Great Flood of 1993 , major portions of

544-526: The area in the 17th century at the time of first French exploration. The French made the earliest European settlement in this region of the Mississippi River Valley . They encountered Illiniwek clans called Cahokia, after whom they named the earthwork complex, and Kaskaskia , after whom the French named a river, a town and a fort. The French villages included Kaskaskia , Cahokia , Prairie du Rocher , St. Philippe, and Prairie du Pont , all under

578-410: The banks became unstable, collapsing into the river due to the powerful current. In this area, the Mississippi became wider and more shallow, which resulted in more severe flooding and lateral changes of the major channel. Several French colonial towns in the 19th century, such as Kaskaskia , Cahokia , and St. Philippe, Illinois, were flooded and destroyed. Kaskaskia was rebuilt but, after the channel of

612-556: The center of the complex and fronting on a 40-acre (160,000 m) Grand Plaza. Monks Mound is the largest Pre-Columbian earthwork in the Americas, and the complex is the largest earthwork north of Mexico. The engineering of the mounds showed that their builders had an expert knowledge of the varying soils and their capacities. Cahokia was a complex, planned, and designed urban center with a residential population, farming, and artisan production of refined crafts and goods. With its location at

646-488: The central precinct and was rebuilt several times. They also discovered two major solar calendars, now known as Woodhenge, as the works were constructed of cedar , which was considered a sacred wood. The area surrounding the mounds had numerous borrow pits from which soil was taken to build the mounds and to fill and level the Grand Plaza and other plazas. After Cahokia was abandoned, there were few indigenous inhabitants in

680-414: The centuries after 600 CE. The Cahokia Mounds Site, which was built as the center attracted a rapid increase in population after 1000 CE, is a six-square mile complex of large, man-made, earthen mounds rising from the flood plain. In 1982, it was designated by UNESCO as one of only eight World Heritage Sites in the United States. The most prominent structure is Monks Mound , rising ten stories high at

714-647: The confluence of three major rivers, it was the center of a regional trading network reaching to the Great Lakes and the Gulf Coast . With a population estimated at 30,000 at its peak, Cahokia was the largest city north of modern-day Mexico . Perhaps for ecological reasons—deforestation and overhunting—the city went into decline after 1300 and was abandoned before 1400. No city in the territorial United States surpassed this population until 1790, when New York City exceeded it. Archaeological investigation has determined that

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748-500: The crust beneath the embayment region cooled, contracted and subsided to a depth of 2.6 km, forming a trough that was flooded by the Gulf of Mexico . As sea levels dropped, the Mississippi and other rivers extended their courses into the embayment, which gradually became filled with sediment. Evidence for this explanation is found in the presence of the seismic zones centered on New Madrid, Missouri, and Charleston, South Carolina , each

782-555: The earliest human civilizations. The present consensus is that "alluvium" refers to loose sediments of all types deposited by running water in floodplains or in alluvial fans or related landforms . However, the meaning of the term has varied considerably since it was first defined in the French dictionary of Antoine Furetière , posthumously published in 1690. Drawing upon concepts from Roman law , Furetière defined alluvion (the French term for alluvium) as new land formed by deposition of sediments along rivers and seas. By

816-413: The embayment's formation was put forward by Van Arsdale and Cox in 2007: movement of the Earth's crust brought this region over a volcanic " hotspot " in the Earth's mantle causing an upthrust of magma which formed the Appalachian-Ouachita range. Subsequent erosion caused a deep trough that was flooded by the Gulf of Mexico and eventually filled with sediment from the Mississippi River. The embayment

850-482: The first Bulgarian Orthodox Church in the United States in Madison, Illinois . Today, East St. Louis is predominantly African-American in ethnicity. Following industrial restructuring, other immigrant descendants moved to other areas when following jobs and housing. Heavy industry is still prominent in the area, although total employment in these industries continues to decline after restructuring and industry changes. Like

884-563: The greatest concentration of bird species in Illinois. The flood plain is bounded on the east by a nearly continuous, 200- to 300-foot high, 80-mile (130 km) long bluff of limestone and dolomite , above which begins the great prairie that covers most of the state. The Mississippi River bounds the Bottom on its west, and the river abuts the bluffline on the Missouri side. Portions of St. Clair , Madison , Monroe , and Randolph counties are in

918-420: The language. The Goshen Settlement was an early American settlement at the edge of the Bottom. The settlers continued to use the rich alluvial floodplain mostly for agriculture until the late 19th century. Brooklyn, Illinois was founded by 1839 as a freedom village by free people of color and fugitive slaves, led by "Mother" Priscilla Baltimore . It was the first town incorporated by African Americans under

952-408: The late 19th century. "Colluvium" is now generally understood as sediments produced by gravity-driven transport on steep slopes. At the same time, the definition of "alluvium" has switched back to an emphasis on sediments deposited by river action. There continues to be disagreement over what other sediment deposits should be included under the term "alluvium". Most alluvium is Quaternary in age and

986-463: The levee; only the spire of the Catholic church and roof of a nearby shrine rose far above the waters. 38°24′N 90°18′W  /  38.4°N 90.3°W  / 38.4; -90.3 Alluvial soil Alluvium (from Latin alluvius , from alluere  'to wash against') is loose clay , silt , sand , or gravel that has been deposited by running water in

1020-517: The protection of Fort de Chartres and Fort Kaskaskia . Examples of 18th-century French Colonial architecture survive here, including the old Cahokia courthouse and Holy Family Catholic Church , both made with the distinctive vertical-log construction known as poteaux-sur-solle . American settlers began arriving near the end of the American Revolution after the Illinois Country

1054-428: The southern Bottom were flooded; 47,000 acres (190 km) of land below Columbia, Illinois was inundated, destroying the town of Valmeyer . The waters came within five feet of overtopping the East St. Louis levee. If they had run over, they would have flooded 71,000 acres (290 km) and destroyed this urban industrial area. More than nine feet of floodwater covered the town of Kaskaskia in 1993 after it overtopped

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1088-421: The various types of mounds were arranged in a planned construction that reflected the cosmology of the Mississippians. The smaller ridge-top and conical mounds were used for ritual burials, some for elites and some for apparent sacrifices. The larger platform mounds were used for temples and homes of the elite. Archaeologists have found remains of a 2-mile (3.2 km) long, defensive wooden stockade that enclosed

1122-553: The water. This resulted in more severe flooding and lateral changes of the major channel, causing the destruction of several French colonial towns, such as Kaskaskia , which relocated; Cahokia , and St. Philippe, Illinois . The southern portion of the American Bottoms is primarily agricultural, planted chiefly in corn, wheat, and soybean. The American Bottom is part of the Mississippi Flyway used by migrating birds and has

1156-423: Was ceded by Great Britain to the new United States. In the early years, American single men came to the country, and there was little government and much anarchy. As Americans arrived, many residents of French descent moved west of the Mississippi River to St. Louis and Ste. Genevieve, Missouri . Within several years, the former French colonial towns had become mostly American in population, and English dominated as

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