Consider the following : I. Abrasion II. Attrition III. Hydraulic action IV. Solution Which of the above are the main types of river erosion ?
- A.I, II and III only
- B.I, III and IV only
- C.II and IV only
- D.I, II, III and IV
Correct answer
Explanation
The correct answer is D, I, II, III and IV. All four are recognised processes by which a river wears away its bed and banks.
Hydraulic action is the sheer force of moving water that loosens rock and forces air into cracks. Abrasion, also called corrasion, happens when the pebbles and sand carried by the river scrape and grind the bed and banks. Attrition is the collision of the transported pebbles with one another, which makes them smaller and rounder downstream. Solution, or corrosion, is the chemical dissolving of soluble rocks such as limestone by river water. Together these processes deepen valleys in the upper course and widen them lower down.
A is wrong because it leaves out solution, which is a major process in limestone areas. B is wrong because it leaves out attrition. C is wrong because it drops abrasion and hydraulic action, the two most powerful processes.
Exam tip: river erosion has four processes, hydraulic action, abrasion, attrition and solution; attrition wears the load itself, the other three wear the channel.
Practice Questions
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Select the correct answer using the code given below:
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Show answer
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