![]() ![]() ![]() Erosion takes place on the outside of bends, creating looping meanders in the soft alluvium of the river plain.Mature rivers (B) are lower-energy systems.Steep-sided “V-shaped’ valleys, waterfalls, and rapids are characteristic features.Young rivers (A) close to their source tend to be fast-flowing, high-energy environments with rapid headward erosion, despite the hardness of the rock over which they may flow.The valley profile now becomes typically ‘U’ shaped with a broad base and a concave slope.As the cycle attains maturity, the lateral erosion (erosion of the walls of a stream) becomes prominent and the valley floor flattens out (attains a ‘V’ to ‘U’ shape).A tributary valley lies above the main valley and is separated from it by a steep slope down which the stream may flow as a waterfall or a series of rapids.The Grand Canyon of the Colorado River in Arizona (USA) runs for 483 km and has a depth of 2.88 km. An extended form of the gorge is called a canyon.Most Himalayan rivers pass through deep gorges (at times more than 500 metres deep) before they descend to the plains.A deep and narrow ‘V’ shaped valley is also referred to as gorge and may result due to downcutting erosion or because of the recession of a waterfall (the position of the waterfall receding due to erosive action).The profile of valley here is typically ‘V’ shaped.The erosional action here is characterized by predominantly vertical downcutting nature.At a young stage, the valley is deep, narrow with steep wall-like sides and a convex slope.At different stages of the erosional cycle, the valley acquires different profiles.The extended depression on the ground through which a stream flows is called a river valley.A braided river, or braided channel, consists of a network of river channels separated by small, and often temporary, islands called braid bars. Braided streams occur in rivers with low slope and/or large sediment load. Braiding: the main water channel splitting into multiple, narrower channel.Vertical, Lateral and Headward Erosion (Kayau, from Wikimedia Commons) Headward erosion: erosion at the origin of a stream channel, which causes the origin to move back away from the direction of the stream flow, and so causes the stream channel to lengthen.Lateral erosion: the erosion of the walls of a stream (leads to valley widening).Downcutting (vertical erosion): the erosion of the base of a stream (downcutting leads to valley deepening).Corrasion or abrasion: solid river load striking against rocks and wearing them down.Attrition: river load particles striking, colliding against each other and breaking down in the process.Corrosion: chemical action that leads to weathering.Hydration: the force of running water wearing down rocks.Various aspects of fluvial erosive action include:.Fluvial Erosional Landforms are landforms created by the erosional activity of rivers.The landforms created as a result of degradational action (erosion and transportation) or aggradational work (deposition) of running water are called fluvial landforms. ![]()
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