Question 8
(a) Outline three differences between deflation and abrasion.
(b) Using specific examples, describe the mode of formation of a deflation hollow.
This was the most unpopular question attempted by the candidates and their performance was very poor.
The description of the mode of formation of a deflation hollow is as outlined below:
- deflation involves blowing away of loose rock wastes while abrasion involves hauling rocks against rock surfaces
- deflation involves rolling loose rock materials along the ground where as abrasion, involves polishing, scratching and wearing away of rock surfaces.
- deflation usually results in lowering of land surfaces while abrasion is most effective at the base of rocks
- deflation is associated with winds while abrasion is associated with winds, water, and waves
- deflation produces land forms such as deflation hollows and oasis, while abrasion produces land forms such as rock pedestal, zeugens, yardangs, etc
- abrasion occurs every where while deflation occurs only in arid and semi-arid regions.
The mode of formation of deflation hollow is:
- it is a feature of arid region
- a product of wind deflation
- a basin or saucer-shaped desert landform
- wind exerts frictional force on loose rocks particles on the surface
- involves the lifting of loose materials from the ground
- it also involves scooping away of loose sandy materials
- the loose materials lifted are blown away
- this action consequently lowers the land surface
- wind eddies help to deepen and enlarge the hollows particularly in soft rock zones
- the enlarged hollows are called depressions or deflation hollows
- they vary in size from some few metres to several kilometres
- the depressions may reach water table to produce oasis or swamps
- e.g. Faiyum in Egypt, Quattarra in Egypt, Baharia in Egypt, Farafra in Egypt, Dakhla in Egypt, Wyoming in USA.