With the aid annotated diagrams, explain the characteristics and mode of formation of the following features:
(a) gorges
(b) self dunes
(a) characteristics and mode of formation of gorges:
* elongated
* steep sided
* can be dry
* also called revines/cayons
* favours the construction of dams
* could be associated with faults
* deep narrow river valley
* can be found in limestones regions
mode of formation:
* formed mostly in the upper course of a river
* formed where waterfall retreats upstream
* formed along fault lines
* presence of alternate bands of hard and soft rocks
* formed where rivers cut deeply along the lines of weakness vertically
* further vertical erosion deepens the valley
* this creates an elongated depression
(b) characteristics and mode of formation of self-dunes:
* found in arid regions
* they are sand deposits
* they are long and narrow ridges
* lie parallel to the direction of prevailing winds
* they lie parallel to each other
* could attain 60 metres in height
* could be over 100km in length
* crests are characterised by peak and saddles
mode of formation
* formed in desert area
* formed due to wind deposition
* sand dunes are deposited parallel to the prevailing wind
* wind blow to clear the corridors between the dunes and sand
* eddies blow towards the side of the corridors
* this results in long parallel mounds od sand called the self dunes
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