ZIMSEC O Level · Geography · Form 2, Form 3
Rock types
- Igneous: formed from cooled magma or lava – granite (coarse, intrusive), basalt (fine, extrusive). Granite covers much of Zimbabwe and forms dwalas (bare domes) and castle kopjes, as in the Matobo Hills.
- Sedimentary: formed from layers of sediment – sandstone, shale, limestone, coal (Hwange), and the Kalahari sands of western Zimbabwe.
- Metamorphic: rocks changed by heat and pressure – marble (from limestone), gneiss (from granite), slate.
- The Great Dyke is a long intrusion of igneous rock rich in chrome and platinum.
Weathering
The breakdown of rock in place.
- Physical: exfoliation (onion-skin peeling of granite from daily heating and cooling), block disintegration, frost action in cold areas.
- Chemical: carbonation of limestone, oxidation and hydrolysis, faster in hot, wet climates.
- Biological: plant roots and burrowing animals.
Rivers
- Upper course: V-shaped valleys, waterfalls (Victoria Falls on the Zambezi), rapids.
- Middle and lower course: meanders, ox-bow lakes, floodplains, levées, deltas.
Processes: erosion (hydraulic action, abrasion, attrition, solution), transportation and deposition.
Exam tip: Use labelled diagrams for landforms – they often earn as many marks as the explanation.
Check yourself
- Name the type of rock that forms castle kopjes.
- Explain exfoliation.
- Name two features of a river's lower course.
Show answers
- Granite (igneous).
- Rock surfaces heat and expand by day and cool and contract at night; outer layers peel off like an onion.
- Any two: meanders, ox-bow lakes, floodplains, levées, deltas.
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