CARA'S TIPSWeathering, mass movement & soils
JAMBWAECNECO
What the syllabus asks
JAMB: Physical Geography D (weathering, mass movement) and H (soils: definition, characteristics, factors and processes of formation, profiles, classification, major tropical types, uses and human impact)
WAEC: weathering (types, processes, factors); mass movement; soils (formation, properties, profile, tropical soil types, erosion and conservation)
NECO: weathering (types, processes, factors); mass movement; soils (formation, properties, profile, tropical soil types, erosion and conservation)
What you will learn
- Distinguish between weathering, erosion and denudation.
- Describe processes of physical, chemical and biological weathering.
- Explain the factors that influence the type and rate of weathering.
- Describe landforms produced by weathering, including inselbergs and tors.
- Classify and describe types of mass movement and their causes.
- Define soil and describe its components and properties.
- Explain the factors and processes of soil formation.
- Draw and describe a soil profile.
- Describe the major tropical soil types, especially in Nigeria.
- Explain the causes, effects and control of soil erosion.
Key points
- Weathering is in situ breakdown; erosion moves material; denudation is the overall lowering of land.
- Physical weathering: exfoliation, block and granular disintegration, frost action, salt crystal growth, pressure release.
- Chemical weathering: carbonation, solution, hydrolysis, oxidation, hydration, reduction.
- Biological weathering: roots, animals, organic acids, people.
- Factors: climate, rock type and structure, relief, vegetation, time, human activity.
- Inselbergs (Olumo, Idanre, Zuma) form by deep weathering then stripping.
- Mass movement: creep, solifluction, earthflow, mudflow, landslide, slump, rockfall.
- Soil = minerals ~45%, humus ~5%, water ~25%, air ~25% (ideal loam).
- Texture: sand, silt, clay; loam is best for most crops.
- Factors of formation: parent material, climate, relief, organisms, time, people.
- Processes: humification, eluviation, illuviation, leaching, laterisation, calcification, gleying.
- Profile: O, A (eluviation), B (illuviation), C, R.
- Nigeria: ferralitic (south), ferruginous (savanna), sandy (far north), hydromorphic and alluvial (swamps, floodplains).
- Erosion types: sheet, rill, gully, wind, splash; gully worst in the south-east.
- Conservation: afforestation, contour ploughing, terracing, cover crops, mulching, controlled grazing, shelterbelts.
Start here: Weathering, erosion and denudation
Look at an old cement block wall in your compound: after many rainy seasons its surface is rough and crumbling. Look at a granite hill such as Olumo Rock in Abeokuta: it has rounded surfaces and loose slabs at its foot. These are signs of weathering.
Weathering differs from erosion. Erosion involves movement: rivers, wind, waves and ice pick up and carry the broken material away. Denudation is the overall wearing down of the land surface by weathering, mass movement and erosion together.
| Weathering | Erosion |
|---|---|
| Rock breaks down in place | Material is moved away |
| No agent of transport needed | Needs a moving agent: water, wind, ice, waves |
| Prepares material (regolith) for erosion and soil formation | Produces features such as valleys, cliffs, deltas |
Why weathering matters
- It produces the regolith (loose weathered layer) from which soils form.
- It shapes landforms (inselbergs, tors, caves).
- It releases minerals (e.g. bauxite and laterite form by deep weathering; clay for pottery).
- It affects buildings, monuments and roads.
- It prepares material for mass movement and erosion.
There are three main types: physical (mechanical), chemical and biological. In nature they usually act together.
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Practice questions
- weathering
- erosion
- deposition
- transportation
Show answer
A: weathering
Erosion involves removal and movement.
- the action of plant roots
- carbonation
- glaciers
- repeated heating and cooling of rock
Show answer
D: repeated heating and cooling of rock
Outer layers peel off, common in hot deserts.
- biological weathering
- mass movement
- physical weathering
- chemical weathering
Show answer
C: physical weathering
Water expands on freezing and splits rock.
- sandstone
- limestone
- granite
- basalt
Show answer
B: limestone
Rain containing carbonic acid dissolves calcium carbonate.
- hot and wet regions
- hot deserts
- polar regions
- high mountains in winter
Show answer
A: hot and wet regions
Heat and moisture speed up chemical reactions.
Key words
- Weathering
- The breakdown and decay of rocks in situ (in place) by physical, chemical and biological processes.
- Denudation
- The general lowering of the land surface by weathering, mass movement and erosion.
- Exfoliation
- Peeling off of outer layers of rock due to repeated heating and cooling.
- Block disintegration
- Breaking of jointed rock into blocks by temperature changes.
- Granular disintegration
- Crumbling of coarse-grained rock (e.g. granite) into grains because minerals expand at different rates.
- Frost action
- Freezing and thawing of water in cracks that splits rock.
- Carbonation
- Reaction of weak carbonic acid in rainwater with limestone, dissolving it.
- Hydrolysis
- Chemical reaction between rock minerals (e.g. feldspar) and water, forming clay.
- Oxidation
- Reaction of minerals (e.g. iron) with oxygen, giving red/brown oxides.
- Hydration
- Absorption of water by minerals, causing swelling.
- Inselberg
- An isolated steep-sided hill rising from a plain, e.g. granite domes near Abeokuta and Idanre.
- Mass movement
- Downslope movement of weathered material under gravity.
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