How are rivers and floods formed?

The landforms of five major rivers and their causes: 1, V-shaped valley: flowing water erosion-the erosion of rivers in the upper reaches and mountainous areas. Because of the large vertical gradient of river bed and high flow velocity, the river has a large vertical component, which can produce strong scouring ability and make the valley deepen faster than widen, thus forming a V-shaped valley on the cross section. 2.u-shaped valley: water erosion-lateral erosion In mountainous areas, when glaciers occupy the front valley or valley, the bottom bed and valley wall are constantly eroded and abraded by glaciers, and the rocks on the slopes on both sides are constantly frozen and weathered, collapsing and retreating, making the original valley turn into a parabola in cross section, so that ice bodies can be discharged more effectively. 3. proluvial (alluvial fan): running water accumulates. Alluvial fan is a fan-shaped accumulation in the estuary. When the river flows out of the valley mouth, it gets rid of the lateral constraints, and the substances it carries are dispersed and deposited. The alluvial fan is fan-shaped on the plane, and the top of the fan extends to the mouth of the valley; Stereologically, it is roughly a semi-buried cone. 4. Floodplain: The accumulation of flowing water is formed by the lateral transfer of rivers and the deposition of floodplain, so the floodplain of plain rivers is relatively developed and wide; The floodplain of mountainous rivers is undeveloped and has a small width, but its relative height is higher than that of plain rivers (see river landform). 5. Delta: The flowing water accumulation delta is an alluvial plain that gradually develops due to the decrease of velocity and the deposition of a large amount of sediment when rivers flow into the ocean, lakes or other rivers. River landform. River landforms are widely developed in the areas where rivers pass, and will show different faces for different geological landforms. Its power source is the same as Danxia landform and karst landform, mainly hydraulic erosion. U-shaped valleys and V-shaped valleys often appear on both sides of rivers. Depending on the hardness of the rock flowing through it. For example, the magnificent Yarlung Zangbo Grand Canyon is a typical V-shaped valley development landform. As for the U-shaped river landform, it can be seen everywhere, mainly distributed in plains and hilly areas. There are also common river landforms, such as river center continent and beach landforms, which are important components of river landforms.