Question

write short note on erosional work of river

Answer 1

Hydraulic action

The pressure of water breaks away rock particles from the river bed and banks. The force of the water hits river banks, and then pushes water into cracks. Air becomes compressed, pressure increases and the riverbank may, in time collapse. Where velocity is high  e.g. the outer bend of meaner, hydraulic action can remove material from the banks which may lead to undercutting and and river bank collapse. Near waterfalls and and rapids, the force may be strong enough to work on lines of weakness in joints and bedding planes until they are eroded.

Abrasion / Corrasion

The sediment carried by a river scours the bed and banks. Where depressions exist in the channel floor the river can cause pebbles to spin around and turn hollows into potholes.

Attrition

Eroded rocks collide and break into smaller fragments. The edges of these rocks become smoother and more rounded. Attrition makes the particles of rock smaller. It does not erode the bed and bank. Pieces of river sediment become smaller and more rounded as they move downstream.

Corrosion / Solution

Carbon dioxide dissolves in the river to form a weak acid. This dissolves rock by chemical processes. This process is common where carbonate rocks such as limestone and chalk are evident in a channel.

Answer 2

he erosional work of streams/rivers carves and shapes the landscape through which they flow. Load carried by a river will grind against its bed and sides. This process slowly wears the bed and sides away. When thrown against the sides and bed of rivers, the load gets broken into smaller pieces.


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