Learning about the Earth with Copernicus Space missions.
The Mississippi river system is one of most complex water bodies system all around the World. The main river is around 3700 km long, its flow is feed by tenths of tributaries and its path cross a large number of states over the entire US territory. Thanks to the eyes of Copernicus Sentinel-2 constellation we have captured some of the most interesting and crucial points of the Mississippi path and this has given the opportunity to understand why and how in a very complex stream system a river can be considered the main stream whereas the others are indicated as the tributaries.
The image above has been sensed during this winter and shows the confluence between the Mississippi (southern stream) and Ohio river (northern) just south of Cairo, Illinois. This stunning sight highlights the different consistency of the two stream, being the Mississippi almost frozen unlike the Ohio: the icy flow is very clear and doesn’t merge the upstream after the confluence point. The difference between the two flows is detected also in other circumstances, as showed in the image below captured in the early December. The Mississippi appears darker than the Ohio river: the colors are of course partly result of the geology of the landscapes they drain or because of a different sediments concentration in the water probably due to different weather conditions faced by the two rivers before the confluence.
At the confluence the the Ohio river is considerably bigger than the Mississippi (volume flow rate 7,960 m³/s vs 5,897 m³/s), indeed it appears as the larger river. This evidence led us to the first question: why is the river called Mississippi even though the Ohio tributary has a larger outflow at the confluence? Despite being the mass/volume flow rate one of the criteria that could be used to define a main stream and a tributary in this case the Mississippi is longer than the Ohio river at the confluence (2,000 km vs 1,579 km), so this is probably one of the reason why the main river is still considered the Mississippi. The river length is indeed one of the main criteria used to define a main steam, together with the drainage basin area.
Anyway, going upstream the Mississippi flow, we face the reverse situation reaching another critical point of this river system: the confluence with the Missouri river in St Louis (Missouri State). Indeed in the animated gif below the Mississippi (the northern stream) flows into the Missouri river: Mississippi looks bigger in terms of flow rate (5,796 m³/s vs 2,445 m³/s) whereas the Missouri is longer than the Mississippi itself (3,767 km vs almost 2000 km). That’s the opposite of the Cairo’s case where the Ohio played the part of the richer but shorter river.
Then the question: why is the Mississippi considered the main river despite the Missouri is longer than the first one and so having a drainage water basin three times larger? Length, mass, drainage area, distance from the sea, angle of impact are all criteria used to define a main stream, with the first one as the common used. But cultural and historical traditions are dominant over geographical theory and this could be the case. Indeed Mississippi is very deep-rooted in many histories and legends of the american and indian native culture since the first settlements and explorations. When the first cartographers and explorers reached the confluence the Missouri’s source was probably still unknown and hided in the Far West (as showed in the image below), just like its major length and its right to be considered the main stream of the river system.