Rivers have various formations along their course. One of these is the meander . This is a curve in the river that forms during the course of tributaries due to the vagaries of the current. The most pronounced curves in rivers are identified as meanders and have a limited duration.
In this article we are going to tell you everything you need to know about the meander, its characteristics and its formation.
Key features
Meanders are used to characterize specific types of rivers based on their shape. There are three types of meanders: braided, straight, and curved or serpentine. In rivers flowing through floodplains, meanders are usually easier to form when the gradient is gentle. This phenomenon can also be observed in the Amazon River , an iconic example of this type of formation.
Sediment is generally deposited in the zigzag bulge and then moves from there to the bank. Erosion dominates in the recesses, and it is obvious how the embankment retreats due to centrifugal force. When the advance of the embankment in the convex area combines with the retreat of the concave area, the river's course begins to shift, and meanders form. An example of a famous meandering river is the Colorado River.
It is easy to identify or distinguish from other types of rivers because its main characteristic is the very obvious meandering curve it forms in its channel . Sometimes, they are named according to the region of their origin. They are called oxbow lakes in the Ebro River in Aragon, and they are called swamps along the Mississippi River in the United States.
When the meandering flow forms a very large curve, it can cause the course of the river to change. They are constantly moving in some areas, such as the plains, so they can form a so-called meander-shaped lake at a certain point. The winding process of each river is different because it depends on its flow, the speed of the water and the materials that make it up.
How the meander is formed
The water in a river always flows in one direction, which is determined by the slope of the terrain on which it moves, although sometimes the surface appears flat.
To test this, you can do a simple experiment. Put water into the pipe; you can see that the rate at which the water replenishes increases or decreases; the rate depends on the slope of the pipe.
The same goes for the river bed. The water flows in the canal; the steeper the terrain, the greater the speed of the water flow and therefore the greater the force on it. It is this force that is eroding the land, causing the river channel to curve.
As the river moves over the porous and permeable surface, the edges of the natural channel through which the river continues to flow erode. As it wears away, it acquires a characteristic concave shape, creating a curve.
According to geologists, the process of meander formation occurs in three steps: corrosion, erosion, and weathering . First, the rapid force or pressure of the water corrodes the riverbank and carries away soil, stones, and rocks.
So this material moved by the force of the water helps to erode the river bed. Finally, the particles of the separated and colliding elements collide; this causes wear, which increases the force that destroys the foundations of the river bed.
Just as outward erosion forms a curve, sediment also accumulates on the opposite bank, forming the convex or inner side of the curve. River channels generally form in the middle and lower reaches of rivers; they rarely occur at the source . This is because it is in the lower or middle part of the river where the current exerts the greatest pressure and force. Meanders can change the landscape and even alter the course of the river.
Meander types
There are very obvious turns and other slight turns; this is due to the centrifugal force of the water as it passes through the bend . The size of the river also has an impact: the larger the river course, the more obvious the twists and turns.
The power of the water can also be reduced. In this case, the curve fills with deposits until the current stops flowing through the sector and the zigzag disappears. Replaced by a "meander-shaped lake," this modified common name. There are several types of meanders:
Embedded meander
It is a type of deep damage to the riverbed rock. When the relief of ocean current circulation increases due to tectonic movement, the meandering waterway resumes its downward erosion process. This process is called rejuvenation.
Meandering valleys are like the valleys that form the Colorado River in the Grand Canyon in the United States, which are perfect examples of how these structures form. When sea level drops, the water droplet can also form an embedded meander. There are two types of embedded meanders:
Meander widened
It is a lateral movement, which is very limited due to the decrease in the baseline level and the consequent decrease in water flow velocity. It has a sedimentary slope on the part that protrudes from the bank and another erosion on the part that extends beyond it.
Valley meander
It is a properly formed meander because it does not cause significant lateral movement. It is created by the flow of water floating over a nearly flat plateau with few depressions. As the river's base water level drops, turbulent currents create deep cuts in the terrain.
Rambling meander
It is a free meander, very common in alluvial plains with few slopes or unconsolidated sediments. This allows the curve to evolve over time; it is considered another type of zigzag.
Cancelled
It is formed when an embedded meander is cut to form a horseshoe-shaped lake. The rest of the land is known by this name. An example is Lake Powell in the southwestern United States, also known as "El Rincón." These horseshoe-shaped lakes originated when the meanders got bigger and began to cross and cross each other. The riverbed does not have an active water flow; Over time, these abandoned river tributaries dry up and fill with sediment.