MEANDER: CHARACTERISTICS, HOW IT IS FORMED AND TYPES - GEOGRAPHY - 2025

The meander is the curve of the river that is formed in the course of the tributaries as a result of the force of the current that drives them. The same term is also often used to define a curve represented in a work of art; however, its most frequent use is linked to the curved shape that rivers take during their movement.

Etymologically, the word meander comes from the Maiandros river. The Greeks gave this name to the river because it had very pronounced curves in its channel. From Greek it passed to Latin as meander, and today it is known as meander. Since that ancient time, the sharp curves in the rivers have been identified as meanders.

Meander of the Amazon river

In literature it has had a metaphorical use. For example, the Argentine writer Jorge Luis Borges used the word "meander" in his works to refer to sinuous themes. Its use in several languages ​​is synonymous with the words curve, bend, sinuous, revolt, undulating, meandering and curved, among others.

Meanders serve to characterize a specific type of river according to its design. There are three types of tributaries: braided, straight and curved or meandering.

characteristics

- Meanders tend to form more easily in rivers that run through alluvial plains where the slope is very low.

- Sediments are often deposited in the convex part of the meander and from there they advance to the shore. In the concave part the erosive action predominates more and it is clearly noticeable how the shore recedes, as a consequence of the centrifugal force.

- By combining the advance of the shore in the convex zone with the retreat in the concave parts, the migration of the channel originates and the meander takes place.

- It is easily recognizable or distinguishable from other types of rivers because its main characteristic is the very pronounced sinuous curve that it makes in the channel.

- Sometimes, depending on the area where they originate, they are named. In the River Ebro de Aragón they are called galachos and in the United States on the banks of the Mississippi River they are known as bayou.

- When the meander forms a very large curve, it can cause the river's course to change.

- They are in constant movement in some areas such as the plains, so they can form at some point what is known as an oxbow lake.

- The process of formation of meanders is different in each river because it depends on its flow, the speed of the current and the materials that make up the channel.

How is a meander formed?

The waters of a river always flow in one direction, which is determined by the inclination of the terrain on which it moves, although sometimes it seems that the surface is flat.

To test it you can do a simple experiment. Water is placed inside a tube and there it can be seen that the speed of the water displacement increases and decreases; speed depends on the inclination of the tube.

The same happens with the river bed. The water runs inside a canal; the steeper the terrain, the greater the speed of the water and, consequently, the greater the force. It is this force precisely what erodes the land, giving the riverbed that curved shape.

As the current of the rivers moves on porous and permeable surfaces, the edges of that natural channel through which the river continues its course are eroded. As it wears, it acquires the characteristic concave shape, thus generating a curve.

Steps in the training process

According to geologists, the process for the formation of meanders occurs in three steps: corrosion, erosion and abrasion. First, the force of the rushing water or hydraulic pressure corrodes the river banks and dislodges dirt, stones, and rocks.

Then, this material moved by the force of the water helps to erode the river bed. Finally, the collision is generated between the particles of the elements that detach and hit each other; this causes an abrasion that increases the power to undermine the foundations of the river bed.

In the same way that it erodes towards the outside forming a curve, sediment also accumulates on the opposite bank creating the convex or internal side of the curve. Meanders are generally formed in the lower or middle course of rivers; they are rarely created in headwaters or headwaters.

This is because it is precisely in the lower or middle part of the rivers where the current brings the greatest pressure and force. Meanders can modify the landscape and even change the course of a river.

Types

There are very pronounced meanders and other milder ones; this is due to the centrifugal force of the water as it passes through the curve. The size of the river also influences: the larger they are, the more pronounced the meanders can be.

The force of the water can also decrease. In this case, the curve fills with sediment until the current stops flowing through that sector and the meander disappears. In its place appears a "oxbow lake", the common name by which this modification is called. There are several types of meanders:

Embedded meander

Meander of the Colorado River, United States

It is one that produces a deep undermining in the rock of the river bed. When the relief through which the current circulates rises due to a tectonic movement, the meandering waterways resume the erosive process downwards. This process is known by the name of rejuvenation.

The meanders turn into a deep valley like the one that forms the Colorado River in the Grand Canyon in the United States. The embedded meanders can also be formed by the descent of the water when lowering the sea level. There are two varieties of embedded meanders:

Meander widened

It is one in which the lateral movement is very limited due to the decrease in the base level and the consequent decrease in the speed of the current. It presents a sedimentation slope on the convex part of the shore and another of erosion on the convex shore.

Valley meander or deepened

It is the meander fitted properly, since it does not have a lateral movement that causes important effects. It is created due to the wandering course of the current on an almost flat plateau without depressions. The rushing waters produce deep cuts in the relief as the river's base level decreases.

Rambling meander

It is a type of free meander that is very frequent in alluvial-type plains with few slopes or on sediments that have not been consolidated. This allows the curve to evolve over time; another type of meander is considered

Meander abandoned

It is when an embedded meander is cut, forming a horseshoe-shaped lake; what remains of the land is known by this name. An example is Lake Powell in the southwestern region of the United States, also known as "El Rincón."

These horseshoe lakes originate as the meanders grow larger and begin to criss-cross and intersect each other. The course of the river is then without active current; over time, these abandoned branches of the river dry up and fill up with sediment.

Bars

They are another phenomenon produced by the constant lateral migrations generated by the loop of a meander. Said loop creates an asymmetrically shaped crest and a depression inside the curves.

References

1. Channel morphology (PDF). Retrieved on June 5, 2018 from vliz.be
2. Types of rivers: Rivers with meanders. Consulted of geovirtual2.cl
3. The river and the way. Introduction to fluvial geomorphology. Consulted of books.google.co.ve
4. Why do rivers meander? Consulted of muyinteresante.es
5. Geology. Consulted from exa.unne.edu.ar
6. Meander. Consulted of es.wikipedia.org