Each stream flows from the source, where it originates, and, gaining strength, ends at the mouth of the river, where it flows into another body of water (ocean, sea, lake, other river or reservoir). It follows from this that the mouth of the river is the place where it joins with another body of water. Some do not have a permanent mouth, sometimes they lose it in the swamp, so it is not always possible to trace the end of the stream.
There is a concept of the so-called blind mouth. It can appear due to drying or when water seeps into the ground, sand, or a river flows into an endorheic lake.
It is customary to distinguish such types of mouths as delta and estuary:
- the river delta owes its appearance to the deposits of erosive products and their removal in large quantities;
- estuary - flooded lower part of the valley.
If the sea is shallow at the mouth of the river, tidal or ebb currents are not expressed and the river carries out a sufficiently large amount of sediment, then we can safely say that nature has created all the conditions for the appearance of a delta.
An example of the largest delta in the world is the mouth of the Amazon. Its area is more thanone hundred thousand km². It is in this delta that another record holder is spread - Marazho, a huge river island, exceeding Scotland in area. The Amazon River is stunning with its mouth, it exceeded the width of the English Channel ten times. Therefore, it is not surprising that during the rainy season the river begins to overflow its banks and thereby flood the surrounding forests. It is very rich in fish and vegetation. There are some animal species that only live in the Amazon. Due to the width, it is not so easy to cross it, it will take about four hours to do this.
Estuaries are formed where there is a sinking of the coast at the mouth of the river. The Ob River boasts the largest estuary. It is called the Gulf of Ob, its length is about 800 km, 50-70 km wide and 25 m deep.
The rivers that flow into the cold seas of the Arctic differ in the types of their mouths. For example, the Lena River and others to the east have deltas. They are pronounced and go far into the seas. Those to the west form estuaries.
The mouth of the Dniester River, which carries its waters to the Black Sea, is characterized by such formation as a firth. And its neighbor Danube formed a delta at the confluence. What factors contributed to this are still a mystery for scientists, the light on which was only partially shed.
A very simple type of delta is the beak delta. It consists of two spits, which are located on both sides of the channel. This type can only be seen on small rivers, for example, in Italy - r. Tiber. Similar braids appeared whenthe speed of the current in the river became small, but the current remained on the rod.
Also, the vaned delta is considered not a very common type. An example of this can be seen on the Mississippi River. Its delta arose due to the furcation of the channel, in this case it has several branches. The prerequisites can be different: from uneven terrain to the influence of the human factor.
These types of deltas are formed when they flow into the sea. There is another species, which is characterized by flowing into shallow bays. Such deltas also have a name - executions. An example is the Danube River. The Niger Delta is very interesting, because its edge has received a smooth contour. The surf of the sea put a lot of effort into this.
