WAEC SSCE - Geography - 2017 (Practical and Physical Geography)

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(a) Characteristics of the stages of a river course

A river is usually divided into three stages from source to mouth.

1. Youthful (upper) stage

• Steep gradient and swift flow; vertical (downward) erosion dominates.
• Deep, narrow V-shaped valleys, interlocking spurs, waterfalls, rapids and gorges.
• Small load of large, angular boulders.

2. Mature (middle) stage

• Gentler gradient; the river erodes both downward and sideways (lateral erosion begins).
• Wider valley, meanders begin to form, and river cliffs and slip-off slopes appear.
• Both erosion and deposition take place; the load is smaller and more rounded.

3. Old (lower) stage

• Very gentle gradient and slow flow; deposition dominates.
• Broad, flat floodplain with large meanders, ox-bow lakes, levees, deltas and estuaries at the mouth.
• Fine load of silt and mud deposited over the plain.

(b) Three ways rivers are beneficial

• Provide water for domestic use, irrigation and industry.
• Serve as routes for inland water transport, and support fishing.
• Used to generate hydro-electric power, and their floodplains provide fertile soil for farming.

Detalles de la respuesta

How the following factors affect the temperature of a place

(i) Latitude

Temperature decreases from the equator towards the poles. Near the equator (low latitudes) the sun's rays strike the earth almost vertically (overhead), so a strong beam of heat is concentrated on a small area and passes through less atmosphere, giving high temperatures. Towards the poles (high latitudes) the rays strike at a slanting angle, so the same amount of heat is spread over a larger area and passes through more atmosphere, losing much of its strength. Hence low-latitude places are hot and high-latitude places are cold.

(ii) Aspect and slope

Aspect is the direction a slope faces. In the northern hemisphere, slopes facing south face the sun and receive more direct heat, so they are warmer; slopes facing north are shaded and cooler (the reverse holds in the southern hemisphere). Regarding slope angle, a surface lying at right angles to the sun's rays receives the rays concentrated on a small area and becomes warmer, while a gently inclined or opposite-facing slope receives slanting rays spread over a wider area and remains cooler.

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(a) Difference between erosion and mass movement

Erosion is the wearing away and removal (transportation) of weathered rock and soil from one place to another by an active agent such as running water, wind, ice or waves. Mass movement (mass wasting) is the downslope movement of rock waste and soil mainly under the direct pull of gravity, without the necessary aid of a transporting agent. In short, erosion needs a moving agent and carries material far away, while mass movement is gravity-driven and usually moves material a shorter distance down a slope.

(b) Four agents responsible for modifying landforms

• Running water (rivers).
• Wind.
• Moving ice (glaciers).
• Sea waves (marine action).

(Underground water is also acceptable.)

(c) Three factors that influence mass movement

• Gradient (steepness) of the slope: the steeper the slope, the faster and more likely the movement.
• Amount of water in the material: water adds weight and lubricates particles, reducing friction and triggering flows and slides.
• Nature of the rock/soil and vegetation cover: loose, unconsolidated material with little vegetation to bind it moves more easily than solid, well-vegetated ground.

Other valid points: earthquakes/vibrations, human activities (mining, road cutting).

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(a) Five sources of water pollution

• Industrial effluents and chemical waste discharged into rivers.
• Untreated sewage and domestic refuse.
• Oil spillage from tankers, pipelines and offshore drilling.
• Agricultural chemicals (fertilisers, pesticides and herbicides) washed into water bodies.
• Mining waste and thermal (hot-water) discharge; also dumping of solid waste.

(b) Five measures to control water pollution

• Treatment of waste: sewage and industrial effluents should be treated before being discharged into water bodies.
• Enforcement of anti-pollution laws: government should make and strictly enforce laws that punish polluters.
• Proper waste disposal: provide dumps, drainage and recycling so that refuse is not thrown into rivers.
• Control of oil spillage: maintain pipelines, monitor tankers and clean up spills promptly.
• Public education and controlled use of agro-chemicals: enlighten people on the dangers of pollution and encourage moderate, correct use of fertilisers and pesticides.

Other valid points: creation of buffer/protected zones around water sources, regular monitoring of water quality.

Detalles de la respuesta

(a) Three characteristics of metamorphic rocks

• They are hard, compact and crystalline.
• They often show foliation or banding (layers of minerals).
• They contain no fossils (any original fossils are destroyed by heat and pressure) and are usually resistant to erosion.

(b) Three modes of formation of metamorphic rocks

• Thermal (contact) metamorphism: rocks are altered by intense heat when they come into contact with rising hot magma, e.g. limestone changing to marble near an intrusion.
• Dynamic (pressure) metamorphism: rocks are altered by great pressure, especially during earth movements and faulting, which crushes and recrystallises them.
• Regional (dynamo-thermal) metamorphism: rocks over a wide area are changed by the combined action of heat and pressure during mountain-building, e.g. shale to slate to schist to gneiss.

(c) Three economic benefits of rocks

• They provide building and construction materials such as granite, marble, sand and gravel.
• They are a source of valuable minerals and ores (gold, tin, iron, limestone for cement) that support industry and earn revenue.
• They weather to form soils that support agriculture, and some (marble, precious stones) are used for decoration and export.