What are the types of landforms formed by rivers

Fluvial landforms are a general term for various erosion and accumulation landforms formed by rivers acting on the earth's surface through erosion, transport and accumulation processes.

Fluvial action is the most frequent and active geomorphological action on the earth's surface, which runs through the whole process of river landform. No matter what kind of rivers are eroded, transported and accumulated, and different types of landforms are formed.

Rivers can generally be divided into three parts: upstream, middle and downstream. The erosion ability from upstream to downstream weakened, and the accumulation gradually increased. There are different types of rivers according to the planar morphology, river type dynamics, and distribution area.

According to the plane morphology, it can be divided into straight type, curved type, split type and wandering type; According to the dynamics of river type, it is mainly divided into two categories: relatively stable and wandering. The river landforms in the mountainous areas and plains have different development and evolution laws and characteristics. The river valleys in the mountainous areas are mostly V or U-shaped, with large longitudinal slope drops, no obvious boundary between the valley floor and the valley slope, and the bedrock is often exposed on the river bank and the river bottom, and most of them are straight river types. There are many thick layers of alluvium in the valley of the plain river, there are intact wide and flat floodplains, the cross section of the river valley is wide U or W-shaped, the longitudinal section of the river bed is relatively gentle, often a smooth curve, the specific drop is small, and most of them are curved, divided and wandering river types.

There are two types of landforms: erosion and accumulation landforms, the former are: erosion riverbed, erosion terrace, valley and valley slope; The latter includes: floodplains, accumulation terraces, alluvial plains, estuarine deltas, etc.

River terraces are important landform types in river landforms, which can be divided into: erosion terraces, stacked terraces (divided into upper and inner terraces), pedestal terraces and buried terraces. The study of the types of river terraces and the structure of their valleys makes it possible to analyze the past of river geomorphology, to understand the present, and to understand the future of river development.

Canyons, terraced topography, coastal plains and estuarine deltas.

Landform: 1. Erosion landform.

Erosion landforms are divided into: downward erosion (erosion of river beds), lateral erosion (erosion of terraces and valleys), and traceability erosion (erosion of valley slopes, extending to the direction of river sources).

1. The downward erosion is generally the most prominent in the upper reaches, because the upstream of the river is mostly mountainous, the drop is large, and the river speed is fast, so the downward erosion is serious.

2. The lateral erosion is the most prominent in the middle and lower reaches, the drop between the middle and lower reaches is small, and the water flow slows down, so the lateral erosion is serious.

3. The root cause of traceable erosion lies in 'downward erosion', so it appears at the source of the river.

2. Accumulation of landforms.

Accumulation landforms are divided into: floodplains (plains), accumulation terraces, flood-alluvial plains, estuarine deltas, etc.

1. The alluvial-alluvial plain is developed in front of the mountain. In mountainous areas, due to the steep terrain, the water flows quickly during the flood period, carrying a large amount of sediment and gravel. When the water flows out of the mountain pass, due to the sudden flattening of the terrain, the river channel becomes open, the water flow slows down, and the material carried by the river is gradually deposited, forming a fan-like accumulation landform, which is called the flood (alluvial) fan landform.

The flood (alluvial) fans continue to expand and connect with each other, forming a flood-alluvial plain.

2. Floodplain (plain): In the middle and lower reaches of the river, rivers accumulate on the convex bank to form an underwater accumulation. The area of the accumulation continues to rise and expand, and the water surface is exposed during the dry season, forming a floodplain.

The flood season is flooded and continues to accumulate. If the river is diverted or eroded downward, the floodplain is abandoned. Multiple abandoned floodplains are joined together to form a floodplain.

3. Delta: When the river carrying a large amount of sediment enters the ocean, the underwater slope of the estuary is gentle, coupled with the supporting effect of seawater, the river flow rate slows down, and the sediment carried by the river will be deposited in front of the estuary, forming a delta.

Influencing factors: the erosion of flowing water is more powerful and widespread, about 90% of the continental area is under the control of the erosion of flowing water, precipitation erodes the surface of the earth, the flow of valleys and rivers, widens and deepens the valley bottom and river bed, and the flowing water on the slope washes the entire slope surface, making it tend to be broken.

Classification of plane morphology.

That is, according to the classification of river type, it is divided into straight type, curved type, split type, and wandering type. (See riverbed topography).

Dynamic classification of river types.

The rivers are divided into two categories: stable and unstable, or relatively stable and wandering, and then divided into straight, curved, and divided according to the plane shape. Classified by region.

It is generally divided into two categories: mountain (including plateau) rivers and plain rivers, which are the most commonly used classifications.

The characteristics of the plain rivers are as follows: the river valley has a thick alluvium, which can reach several meters or several hundred meters; Most of the valleys have intact floodplains, the valley slopes are relatively gentle (except for the local narrow valleys), and there is generally no obvious boundary between the valley floor and the valley slope, but there is still a clear boundary between the riverbeds under different water level conditions. The riverbed section is mostly in the shape of U or wide W (Fig. 2), which is relatively wide and shallow. The riparian morphology is relatively regular, but easy to change; The longitudinal profile of the river is relatively gentle, often a smooth curve, and the specific drop is small; According to the natural conditions, the river type develops into straight, curved, divided, wandering and other river types, and the transformation between them can occur due to the change of conditions, which is rare in mountain rivers. Many micro-landforms are formed in the riverbed, such as sand waves.

Plains rivers are rivers that flow through flat terrain. The plain itself is mainly formed by the accumulation of large amounts of material carried by the water flow, and then due to climate change or tectonic uplift, the river slightly cuts into the original accumulation layer, forming an open river valley, and often leaves traces of accumulation terraces on the valley slope. The accumulation of rivers forms a delta in the estuarine section, which continues to extend and expand, forming a vast alluvial plain.

Characteristics of river landform in mountainous areas: The cross-section morphology of river valleys often develops into a V-shaped or incomplete "U" shape (Fig. 1), and the valley slopes on both sides are steep, and the slopes are straight or curved. There will be one or more levels of river terraces in the river valley, which are generally narrower and have fewer steps; There is often no obvious boundary between the valley floor and the valley slope, and there is often no obvious dividing line between the riverbed under different water level conditions. There are often strong rocks protruding from the banks and the center of the river, the shoreline is extremely irregular, and there are often deep meanders developing; The longitudinal section of the river is steep, the form is very irregular, the deep trough of the rapids is staggered up and down, often in a stepped curve, and a steep slope or waterfall is often formed in the concentration of drops. Mountain rivers are generally not navigable, but have abundant water resources.

The characteristics of the plateau river landform are slightly different from those of the mountain rivers: the riverbed is not deeply cut; The valley bottom retains the wide valley form of the original ground, with obvious river valley bottoms, and the valley slopes on both sides of the wide valley are gentle, and the valley floor width is several kilometers or wider. The modern riverbed is hundreds of meters wide, the flow path is scattered, and the diversion is frequent; The river type is dominated by free bending and splitting river types.

It is understood that the landforms of rivers mainly include: river valleys, mountain rivers, estuaries, riverbeds, river beaches, river ditches, etc.