WAEC SSCE - Geography - 2020 (Practical and Physical Geography)

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(a) Definition of weathering

Weathering is the breakdown, decay or disintegration of rocks in situ (at or near the earth's surface) by physical, chemical and biological processes, without the transportation of the resulting materials. It is distinct from erosion, which involves movement of the loosened material.

(b) Three factors that affect weathering

1. Climate: temperature range and moisture control the type and rate; alternate heating and cooling favours physical weathering, while heat and rainfall favour chemical weathering.
2. Nature of the rock (rock type and structure): hardness, mineral composition and the presence of joints and bedding planes determine how easily a rock breaks down.
3. Vegetation and living organisms: plant roots prise rocks apart and decaying organic matter produces acids that attack minerals.

(Relief/slope and time are also acceptable.)

(c) The process of exfoliation

Exfoliation is a form of physical weathering common in hot deserts and tropical regions with large diurnal temperature ranges. The process is:

• By day, intense heating causes the outer surface layer of the rock to expand more than the cooler interior.
• At night the surface cools rapidly and contracts.
• This repeated expansion and contraction sets up stresses between the outer shell and the inner rock, weakening the bond between them.
• In time the outer curved layers peel or flake off like the layers of an onion, a process aided by slight chemical action of dew.
• The result is smooth, rounded rock masses such as exfoliation domes, with the peeling shells accumulating at the base.

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(a) Five factors that affect climate

1. Latitude (distance from the equator): places near the equator receive more direct, intense insolation and are hotter than places near the poles.
2. Altitude (height above sea level): temperature falls with height (about \(6.5^{\circ}\text{C}\) per \(1000\text{ m}\)), so highlands are cooler than lowlands.
3. Distance from the sea (continentality): coastal areas have a small temperature range while interiors have hot summers and cold winters.
4. Ocean currents: warm currents raise the temperature and rainfall of adjacent coasts, while cold currents lower them.
5. Prevailing winds and relief (aspect): onshore moist winds bring rain, offshore dry winds do not, and windward slopes are wetter than leeward slopes.

(Vegetation cover and cloud cover are also acceptable.)

(b) Five characteristics of the Equatorial climate

1. High temperatures all year: mean monthly temperature is about \(27^{\circ}\text{C}\), with a very small annual range (about \(2^{\circ}\text{C}\)).
2. Heavy rainfall throughout the year: totals exceed \(2000\text{ mm}\), with no true dry season (double maxima near the equinoxes).
3. High relative humidity: often above 80 per cent, giving a hot, damp, uncomfortable feel.
4. Convectional rainfall: intense afternoon thunderstorms occur almost daily due to strong heating and rising moist air.
5. Small diurnal and seasonal contrast with heavy cloud cover: days are consistently hot, humid and cloudy with little seasonal variation.

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(a) Five landforms found in the upper course of a river

1. V-shaped valley (deep, narrow valley cut by vertical erosion).
2. Interlocking spurs (projecting ridges the river winds around).
3. Waterfalls (and rapids where the river crosses hard rock bands).
4. Gorges (steep-sided rocky valleys, often below a retreating waterfall).
5. Potholes (circular hollows drilled into the rocky bed by swirling pebbles).

(Cascades and cataracts are also acceptable.)

(b) Alluvial fan and delta compared

Three differences

Two similarities

1. Both are depositional landforms built from river load (alluvium).
2. Both are formed where the river's velocity and carrying capacity fall sharply, and both have gentle, fan-like or spreading shapes crossed by distributaries.

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(a) Two differences between weather and climate

(b) Instruments used to measure the weather elements

• (i) Sunshine: the Campbell-Stokes sunshine recorder.
• (ii) Rainfall: the rain gauge.
• (iii) Cloud cover: estimated by the eye in oktas (eighths) of the sky (an instrument such as a nephoscope observes cloud movement).

(c) How wind speed is measured and recorded

• Wind speed is measured with a cup anemometer, which consists of three or four hemispherical cups mounted on horizontal arms that rotate freely on a vertical spindle.
• The wind pushes the cups round, and the rate of rotation is proportional to the wind speed.
• The rotations are transmitted to a dial or counter which is calibrated to read the speed in kilometres per hour, metres per second or knots.
• The instrument is mounted in an open, exposed place about \(10\text{ m}\) above the ground, free from obstruction.
• Readings are taken at fixed times and recorded; average and gust speeds may be logged, and on the Beaufort scale the values are expressed in numbered wind forces.