Stream erosion brings enormous changes within the landscape of its passage. The power of water gets succeeded in order to remove all kinds of obstacles before its way. It cuts the rocks, erodes the ledges, digs out trenches. Stream water brings many changes to the channel it passes through. Following are the main features of stream erosion.
Pot-holes are the circular and deep holes, cut into solid rocks by sand grains and pebbles, swirling in fast eddies. They are commonly found on the channel flow. In steep rock when the rainwater flows with high velocity, the water strikes on the extended surface, and starts eroding the surface. After passing long period of time, it makes a hole on the floor of channel on rock surface.
The falling of stream water from a height is called a waterfall. Waterfalls occur at places where the stream profile makes a vertical drop. Such a situation is usually found where gently inclined, erosion resistant bed over-lie the nonresistant beds. The softer rock is eroded fast while the harder one offers resistance and forms a ledge at a height, from which the stream’s water falls down deep into the gorge. When the water falls over the ledge, it erodes the less resistant bed of cliff. Due to this undercutting a portion of the upper resistant bed breaks off and the waterfall retains its vertical cliff while it gradually moves upstream. Niagara fall of USA have retreated approximately 11 kilometers upstream since its formation.
A narrow valley with steep, rocky walls located between hills or mountains called a gorge. The word has been taken from French language, which means throat. As throat is a deep place of mouth, therefore, gorge is used against the deep and steep trench made by stream flow. The gorge differs from a canyon, because of its smaller size. A canyon is larger than a Gorge. However both the words are used for a deep and narrow valley with a stream channel along its bottom.
The symmetrical S-shaped loops, founding the course of a river, are called Meanders. Meanders develop in mature rivers. Mature rivers are those which have cut down to an approximately graded profile. In such rivers-sides cutting becomes very prominent which results in the development of meanders. The meanders grow due to deposition of sediment along the slip-off side and erosion at the undercut side.
Meanders continually change their position. They move both down-stream and to the sides. The side ways movement occurs because at bends the swiftest currents shift toward the outside band causing erosion at the outside of the curve and deposition on inside of the curve. In this way a stream migrates sideway and slightly downstream by eroding its outer bank and depositing a san bar at the inner bank.
The meander is grown by eroding its outer bank and depositing sediments at the inner bank. During this process the sharpness of the river bends increases progressively and the neck of meander becomes narrow and narrow. Finally a stage comes when the river cuts through the neck and starts flowing straight leaving behind its roundabout course. Such left out old meanders which remain filled with stagnant water, are called “Oxbow Lakes”.
On many occasions, the land is uplifted. The uplifting of a mature stream would cause it to give up lateral erosion and revert to down-cutting. Rivers of this type are said to be “rejuvenated”. When a meandering river is rejuvenated, it starts down-cutting again. As a result the meandering channel is deepened and the old meanders get entrenched into the bedrock. Such meanders are called “entrenched meanders”.