How a river erodes

Good day steemit friends, In my previous post i explained how a river grow. Today i will be writing on how a river erodes.
As a river flows down its channel, it erodes or degrades this channel. It does so in four ways:

• It uses sheer force of its currents to break off rock particles from the channel bedrock. This process is called hydraulic action. At a very high stream velocity and pressure, for example, where the channel becomes constricted, in a dam spillway or at the base of the waterfall, hydraulic action becomes intense and is then called cavitation.

• The river carries along the broken off rock pieces, and uses them as tools to chisel off more rock particles from the channel bedrock. This is called corrasion or abrasion.

• The particles themselves hit against one another and against the bedrock at the floor and sides of the channel, and break and wear themselves down into smaller and rounder pieces in a process known as attrition.

• Finally, where a river containing a weak acid solution flows over a limestone area, it dissolves the limestone in a chemical action known as corrosion or solvent action. In similar way, the river chemically dissolves organic acids from decaying vegetable matter in its channel.
  
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By these processes of stream erosion, the river channel is eroded in three directions; headward, laterally (or erosion of the channel sides), and vertically ( or deepening of the channel floor). Erosion of the river bed around the boulder creates a hole at the bed underneath the boulder, more clearly seen when the boulder has been pushed on. This hole is called a pothole. It is coalescence of several potholes that actually helps deepen the river bed. Stream erosion is sometimes called stream degradation.

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