How is mississippi river formed

Beyond the beauty of our bluffs, the underlying limestone is also responsible for the sinkholes that occur throughout southwestern Illinois and on our properties. Rainfall absorbs carbon dioxide making water slightly acidic and capable of dissolving the minerals in limestone. Over time, the water carves out underground streams which form into caves. From million years ago to current day, most of Illinois remained above sea level preventing the formation of new sedimentary rock.

Although we lack fossil evidence, dinosaurs roamed across most of Illinois during the Mesozoic era — 66 million years ago. Erosion and multiple glaciations erased any fossil evidence of the dinosaurs. The supercontinent Pangea broke apart during the Jurassic period — million years ago and the continents slowly settled into their current positions.

Now that the background has been covered, we can start talking about the age of the Mississippi River. I asked a few other biologists and even called a couple local museums in my search for answers. I received differing answers with marginal confidence. So, I dove deep into internet resources and borrowed several books from my local library. Still, I did not found a definitive answer. I decided that I must use my favorite multiple choice test strategy, the process of elimination.

Outside of some technicalities, we can say that the Mississippi River was not formed while Illinois was under water. In western North America, The Rocky Mountains were being thrust upward as late as 40 million years ago. Therefore, the Mississippi River is less than 40 million years old. Now, we are going to approach the question from the other direction. During the Illinoisan and Wisconsinan glaciations , to 10, years ago , glacial till and moraines created dams that rerouted the Mississippi River to the west.

Most of the present-day landforms developed during the multiple glacial episodes that occurred during the Wisconsin Glaciation. Therefore, an overview of the glacial history of Minnesota is necessary to provide a context for discussing geologic development of the river in the MNRRA corridor. However, exposures of pre-Wisconsin drift occur at the surface in Washington and Dakota Counties.

A system of well-integrated stream networks, forming a dendritic branch-like pattern across the region, drains the uplands. Erosion along stream valleys has exposed a considerable amount of bedrock. It is uncertain when the upper Mississippi River valley initially formed. However, on the basis of present geologic evidence, deep cutting must have occurred during the early Pleistocene. Researchers investigating stream valleys of the Driftless Area in southwestern Wisconsin suggest deep valley incision by streams also occurred during the early Pleistocene.

Wisconsin Glaciation 35,, B. Paul has been obscured by late Wisconsin glacial events. The course of the river north of St. Paul changed repeatedly during the Pleistocene. Previously formed bedrock valleys were subsequently filled with glacial sediment derived from the Superior Lobe and Grantsburg Sublobe.

The numerous lakes dotting the landscape within the Twin Cities area resulted from meltout of glacial ice blocks buried in the bedrock valleys Figure 4. During the late Wisconsin maximum, the Superior Lobe advanced down the axis of the Lake Superior basin southeastward to its terminal position near Minneapolis and St.

This advance, known as the St. Croix phase of the Superior Lobe, culminated approximately 15, years B. Croix Moraine, a massive accumulation of glacial sediment extending from the Twin Cities northwestward to Little Falls, marks the terminus of the lobe.

It is unclear where the position of the Mississippi River was at this time. The Mississippi River presently occupies a prominent gap eroded through the St. Croix Moraine. Most likely the river maintained its current position below St.

Paul by continued flow underneath the advancing ice margin. Glacial outwash graded to terrace deposits along the Mississippi River in southern Washington County lends support to this hypothesis. Croix Moraine forms a northeastward trending, rugged belt of landforms containing numerous hills and associated depressions. Glacial sediment deposited during this advance consists of reddish-brown sandy till, outwash sand and gravel, and ice-contact sands and gravel.

As the Superior Lobe retreated from the area, the Mississippi and St. Croix Rivers acted as the major course for the glacial meltwater. Outwash deposits filled both valleys between an elevation of and feet. Meltwater streams subsequently excavated the outwash deposits during a later glacial advance. Numerous readvances, possibly surges, accompanied the retreat of the Superior Lobe from the St. The Mississippi River, in the central portion of the state, flowed along the western margin of the St.

Croix Moraine, being fed by tunnel valleys discrete meltwater channels developed underneath the retreating ice lobe. Retreat of ice farther into the Lake Superior basin resulted in deposition of long, sinuous ridges of sand and gravel eskers within the tunnel valleys Figure 5c. The next major advance of the Superior Lobe, the Automba phase, is marked by advance of the Superior Lobe into the Mille Lacs region of east central Minnesota Figure 5d.

The Automba phase is correlated with the Tiger Cat advance in Wisconsin. Croix River into the Mississippi River valley. While the Superior Lobe stood at the Mille Lacs Moraine, meltwater ponded along the northwestern margin of the ice lobe, resulting in the formation of glacial lakes Aitkin I and Upham I, which presumabably drained along the western end of the ice margin. The advance of the St. Louis Sublobe across the area erased any shoreline features that developed along the lakes.

However, evidence for these lakes is preserved in a thin, red and gray, stone-poor till deposited by the St. Louis Sublobe after overriding the lake plain.

Any evidence of the location of the Missisisppi River channel in the area was destroyed by subsequent ice movements; however, it is most likely that meltwater was still channeled along the outer margin of the St. Croix Moraine down to the Mississippi valley below St.

The Superior Lobe retreated from the Automba ice margin into the Superior lowland, initiating the first stage of glacial lake formation in the Superior basin.

Glacial lake sediments were deposited in a large body of open water, which formed between the retreating Superior Lobe and higher topography to the southwest. Fine-grained silt and clay settled out of the melting ice mass, forming a continuous blanket of sediment on the lake floor. The next advance of the Superior Lobe overrode the lakebed during the Split Rock phase, depositing a thin layer of reddish clay across previously formed deposits. Retreat of the Superior Lobe was followed by advance of the Des Moines Lobe from the northwest during the Pine City phase, which reached its maximum extent in central Iowa about 14, years B.

An end moraine near the city of Des Moines marks the terminal position of the ice lobe. During this advance, outwash channels were cut through portions of the St. Croix Moraine, forming sand and gravel deposits that reached the Mississippi River near Hastings. The Grantsburg Sublobe, an offshoot of ice developed from the Des Moines Lobe, advanced from the southwest overriding the St. Croix Moraine between St. Cloud and St. Paul, reaching its terminus near Grantsburg, Wisconsin, by about 13, years B.

Figure 6. This short-lived advance was responsible for altering the geologic development of the Mississippi River valley in two important ways. First, outwash coming off the advancing lobe filled the Mississippi River valley with sand and gravel. The deposits would later be entrenched by glacial meltwater forming a series of flat-lying terraces between elevations of and feet along the valley.

Second, advance of the lobe blocked the southward drainage of the Mississippi, resulting in the formation of glacial Lake Grantsburg. While the Grantsburg Sublobe occupied east central Minnesota and west central Wisconsin, meltwater draining south flowed into glacial Lake Grantsburg. A large delta was formed near Spooner, Wisconsin, as sediment-laden meltwater entered the head of the lake.

The lake drained down the St. As the Grantsburg Sublobe retreated to the southwest, meltwater drained around the outer northeast margin of the ice lobe, reworking the former lake bed and forming the Anoka Sand Plain in east-central Minnesota Figure 5f. Farther south, retreat of the Des Moines Lobe was punctuated by a number of readvances, forming a series of discontinuous moraines in northern Iowa and southern Minnesota.

By 12, years B. A large braided meltwater stream developed along the retreating Grantsburg ice margin, forming a continuous blanket of sand and gravel along the present course of the Mississippi River above its confluence with the Minnesota River. As ice retreated further, the level of the Mississippi and Minnesota Rivers was established at an elevation of about feet in the Twin Cities metropolitan area. The last major glacial advance in Minnesota occurred during the Nickerson-Alborn phase when the St.

Retreat of the St. Louis Sublobe allowed glacial lakes Aitkin and Upham II to develop, ponded between the ice margin and the Culver moraine. Louis and Mississippi Rivers. A broad outwash plain extends off the Nickerson Moraine southward where it coalesces into a fairly well defined channel along the Kettle River.

The Kettle channel drained meltwater into the St. Croix River and then down to the Mississippi. Ice then readvanced a short distance to form the Big Stone Moraine in west-central Minnesota about 11, years B. After the ice retreated north of the divide that separates the Hudson Bay and Mississippi drainages, glacial Lake Agassiz came into existence.

In northeastern Minnesota, the Superior Lobe retreated from the Nickerson ice margin into the Superior Lowland, initiating the formation of glacial Lake Duluth. Drainage of sediment-free meltwater from glacial Lakes Agassiz and Duluth resulted in multiple downcutting events within the Mississippi River valley.

A number of geologists have been active in working the drainage relationships of these lakes and their impact upon the landscape. Below is a summary of these works and how the events associated with glacial lake drainage affected the morphology of the upper Mississippi system.

River Warren was named after G. Warren, the first commander of the St. Paul District, Corps of Engineers. Above St. Below St. Paul, the River Warren intercepted a preglacial bedrock valley of the Mississippi River that was filled with outwash up to the elevation of the Platteville Limestone.

The discharge of River Warren was more than adequate to carry the sediment load supplied to it; therefore, the unconsolidated outwash sediment was rapidly eroded from the preglacial valley. Once the outwash was carried away, a waterfall formed where the River Warren plunged over the Platteville Limestone into the preglacial bedrock valley. The waterfall was named River Warren Falls in honor of the mighty river that was responsible for its formation. Glacial ice, advancing again across the continental divide, caused a build up of sediment within the River Warren, the St.

Croix, and presumably the Mississippi valleys approximately 11, years B. Glacial Lakes Agassiz and Superior reformed after 11, years B. Discharge of meltwater out of the lakes established a fairly active period of downcutting that lasted until approximately 10, years B. One final advance of ice blocked eastern outlets and caused renewed downcutting within the Mississippi valley between 9, and 9, years B.

This final episode is the last time that meltwater from glacial lakes flowed down the upper Mississippi River system north of Illinois. These events played a vital role in the Holocene evolution of the Mississippi valley.

Early Holocene 9,, years B. Peter Sandstone that underlay limestone caprock Figure 4. Paul the valley had been cut far below its present-day level, possibly up to 50 meters about feet deep. Sediments stored in tributary valleys were soon transported into the Mississippi River, resulting in a fairly active period of alluviation. More sediment entered the Mississippi from its tributaries than the big river could carry away.

As a result, a number of tributaries built fan deltas into the Mississippi River, deflecting its course and altering the physiography of the floodplain. A good example of a tributary delta occurs at the confluence of the Mississippi River with the Chippewa River in Pepin County, Wisconsin. The formation of the delta effectively dams the Mississippi River, forming Lake Pepin. Zumberge proposed that Lake Pepin once extended upstream to St. Paul, based on the existence of clay deposits found in borings taken during the construction of the Robert Street Bridge in St.

Equilibrium between the Mississippi River and its tributaries began to establish itself by 8, years B. By this time, the River Warren Falls had reached the Minnesota River valley, where it split into two parts.

The River Warren Falls continued to retreat up the Minnesota River valley an additional two miles, where it intersected a buried valley of the preglacial Mississippi died out. Anthony Falls developed at the confluence of the Minnesota River near Fort Snelling and retreated up the valley of the Mississippi Figure 4.

Middle Holocene 7,, years B. Vegetation was well established on upland areas by this time. Therefore, the change in upper midwestern rivers was most likely related to climatic effects on river discharge rather than changes in vegetation. Geomorphic processes acting in the valley were vari- able along the entire stretch of the upper Mississippi River.

The upper reaches were characterized by vertical accretion built up of sediment, while lateral channel migration and incision into previously deposited sediment were occurring in downstream reaches. As the middle Holocene progressed, climatic changes would again alter the processes acting within the valley. Cooler temperatures and increased precipitation began to dominate the regional climate, which may have initially increased runoff.

In response, active lateral channel migration and incision dominated fluvial processes acting in the valley. Late Holocene 3, years B. However, fluvial processes varied with location along the valley. Vertical accretion dominated various portions of the valley, while lateral channel migration, or cut and fill sequences, dominated other parts.

This topography contrasts strongly with the Lower Mississippi, which is a meandering river in a broad, flat area, only rarely flowing alongside a bluff as at Vicksburg, Mississippi. The Middle Mississippi is a relatively free-flowing river. Louis to the Ohio River confluence, the Middle Mississippi falls a total of feet 67 m over a distance of miles km for an average rate of 1. At its confluence with the Ohio River, the Middle Mississippi is feet 96 m above sea level.

Thus, by volume, the main branch of the Mississippi River system at Cairo can be considered to be the Ohio River and the Allegheny River further upstream , rather than the Middle Mississippi. The widest point of the Mississippi River is in the Lower Mississippi portion where it exceeds 1 mile 1. The basin covers more than 1,, sq mi 3,, km2 , including all or parts of 32 U.

The drainage basin empties into the Gulf of Mexico, part of the Atlantic Ocean. The retention time from Lake Itasca to the Gulf is typically about 90 days. Fresh river water flowing from the Mississippi into the Gulf of Mexico does not mix into the salt water immediately. These images demonstrate that the plume did not mix with the surrounding sea water immediately.

Instead, it stayed intact as it flowed through the Gulf of Mexico, into the Straits of Florida, and entered the Gulf Stream. The Mississippi River water rounded the tip of Florida and traveled up the southeast coast to the latitude of Georgia before finally mixing in so thoroughly with the ocean that it could no longer be detected by MODIS. Prior to , the Mississippi River transported an estimated million metric tons of sediment per year from the interior of the United States to coastal Louisiana and the Gulf of Mexico.

During the last two decades, this number was only million metric tons per year. The reduction in sediment transported down the Mississippi River is the result of engineering modification of the Mississippi, Missouri, and Ohio rivers and their tributaries by dams, meander cutoffs, river-training structures, and bank revetments and soil erosion control programs in the areas drained by them.

Over geologic time, the Mississippi River has experienced numerous large and small changes to its main course, as well as additions, deletions, and other changes among its numerous tributaries, and the lower Mississippi River has used different pathways as its main channel to the Gulf of Mexico across the delta region.

Through a natural process known as avulsion or delta switching, the lower Mississippi River has shifted its final course to the mouth of the Gulf of Mexico every thousand years or so. The abandoned distributaries diminish in volume and form what are known as bayous. This process has, over the past 5, years, caused the coastline of south Louisiana to advance toward the Gulf from 15 to 50 miles 25—80 km. The currently active delta lobe is called the Birdfoot Delta, after its shape, or the Balize Delta, after La Balize, Louisiana, the first French settlement at the mouth of the Mississippi.

The southernmost extent of this enormous glaciation extended well into the present-day United States and Mississippi basin. When the ice sheet began to recede, hundreds of feet of rich sediment were deposited, creating the flat and fertile landscape of the Mississippi Valley.

During the melt, giant glacial rivers found drainage paths into the Mississippi watershed, creating such features as the Minnesota River, James River, and Milk River valleys. Ice sheets during the Illinoian Stage about , to , years before present, blocked the Mississippi near Rock Island, Illinois, diverting it to its present channel farther to the west, the current western border of Illinois. Saturday, November 13, Sign in.

Forgot your password? Get help. Password recovery. Geology Page. Home Latest News Video. Debris Flow Dynamics.