Deflation Hollow. Image via Imgkid

Deflation Hollow. Image via Imgkid

ZIMSEC O Level Geography Notes: Deflation Hollows

  • Are also known as closed hollows or blowouts.
  • These are enclosed depressions caused by wind erosion.
  • In deserts the wind erodes loose material from flat areas which have, uncemented sediments such as those occurring in tropical deserts.
  • Deflation hollows develop in areas where the transported materials is deposited.
  • As already mentioned deposition occurs when the wind meets with an impediment.
  • Deflation hollows are usually formed on surfaces patches where the protective vegetative cover has been lost for example due to human activities or periods of extended droughts.
  • Since that portion becomes unprotected the the wind deflates and scours continuously at relatively unconsolidated material,
  • The material is deposited on the edges of the hollow that are still protected by vegetation such as marram grass.
  • The removal of the fine particles the lowering of the landform leads to the formation of a depression.
  • An example is the Qattara Depression
The formation of a Deflation Hollow.

The formation of a Deflation Hollow. Image credit Revisionworld.com

  • Sometimes water that falls in these depression hollows during freak storms collects to form pools in the midst of deserts providing an essential source of water for local ecosystems, animals and humans and their activities.
  • If an area is eroded down to the water table, further deflation is prevented unless the water table is also lowered by evaporation.
A diagram showing the formation of deflation hollows.

A diagram showing the formation of deflation hollows.

  • Some oases in the Sahara were formed in this manner and may be below sea level.
  • Dunes are made from sand that is deposited at the leeward side of the wind.
  • Some deflation hollows may be formed in part due to the presence of faults within the rocks which are exploited and widened by weathering and the regolith removed by wind erosion.
An Oasis, note the dunes on the leeward side of the  Oasis. Image credit Travelingmyself.com

An Oasis, note the dunes on the leeward side of the Oasis. Image credit Travelingmyself.com

  • Note note all oasis are formed by deflation some are naturally occurring springs and some result as a result of freak storms and the underlying geological rocks limiting the amount of infiltration.

To access more topics go to the Geography Notes page.

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