ZIMSEC A Level · Geography · Form 5
Plate tectonics
Constructive, destructive and conservative margins; the East African Rift Valley shows continental rifting. The Zambezi valley lies in a rift-faulted trough.
Weathering
- Physical: exfoliation (granite domes), block and granular disintegration, salt crystallisation.
- Chemical: hydrolysis (feldspar to clay – important in granite), oxidation, carbonation and solution.
- Biological: roots and organisms.
Climate controls weathering: chemical weathering is deep and rapid in hot, humid conditions (deep regolith in the tropics).
Granite landforms
- Inselbergs: isolated hills rising from plains.
- Bornhardts (dwalas): dome-shaped bare rock, e.g. in the Matobo Hills.
- Castle kopjes and tors: piles of rounded boulders formed by deep chemical weathering along joints followed by stripping of the regolith (two-stage theory, Linton).
Slopes
Slope form depends on rock, climate, vegetation and processes: mass movement (soil creep, landslides, mudflows) and surface wash. Parallel retreat and slope decline models explain change over time.
Pediments and pediplains
Gently sloping rock surfaces at the foot of hills, formed by scarp retreat in semi-arid climates (King's model).
Exam tip: Use the deep-weathering (two-stage) theory to explain kopjes – it is a common essay question.
Check yourself
- Which chemical weathering process breaks down feldspar in granite?
- Name a Zimbabwean area with dwalas and castle kopjes.
- Explain the two-stage formation of tors.
Show answers
- Hydrolysis.
- The Matobo Hills (also around Harare, e.g. Domboshawa).
- Deep chemical weathering along joints under a humid climate forms corestones in regolith; later erosion strips the regolith, exposing the boulders.
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