SS2 First Term Geography Lesson Note – Action of Winds

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WEEK 3      

TOPIC:  ACTION OF WINDS

CONTENT:  

1. Processes of wind erosion
2. Features of wind erosion and their mode of formation.

SUB-TOPIC 1: PROCESSES OF WIND EROSION

Erosion takes place mainly by winds in deserts. Wind erosion involves the removal or wearing away of rocks in desert by wind energy or blowing wind.

The main agent of erosion in the desert is the wind. Wind erosion takes place through the process of: (i) Deflation (ii) Abrasion (iii) Attrition

1. DEFLATION: This is the lifting and blowing away of loose sand and pebbles by wind. Deflation results in the lowering of the land surface to form large depressions called deflation hollows.
2. ABRASION: This is the process whereby sand particles carried by wind are used to blast or wear away rock surface as in rock pedestal, zeugen and yardang.
3. ATTRITION: This is the process whereby wind-borne particles collide with one another, resulting in the wearing away of each other. This results in the reduced round sizes of the particles.

SUB-TOPIC 2: FEATURES OF WIND EROSION AND THEIR MODE OF FORMATION

As the wind removes or wears away rock in the desert through the processes of deflation, abrasion and attrition certain features are formed. The following are some of the features of wind erosion:

1. Rock Pedestals or Mushroom Rocks: The sand blasting effect of winds against any projecting rock masses wears back the softer layer so that an irregular edge is formed on the alternate bands of hard and soft rocks. Continuous wind abrasion produces a mushroom like rock called rock pedestals. They are common in the Tibetan Mountains of Central Sahara desert and the devil’s rock in Niger Republic.
2. Zeugen: These are tabular masses which have a layer of soft rock lying beneath a surface layer of a more resistance rock. The effect of wind abrasion wears them into a ridge and furrow landscape. Examples are found in Northern Nigeria, Kalahari Desert and Western Australia.

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