WAEC SSCE - Geography - 2014 (Practical and Physical Geography)

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(a) Processes of river erosion:

1. Corrasion (abrasion): the wearing away of the bed and banks by the load (sand, pebbles) the river carries and hurls against them.
2. Attrition: the load particles knock against one another and are broken into smaller, rounder pieces.
3. Hydraulic action: the sheer force of the moving water loosens and drags away materials from the bed and banks. (Also corrosion/solution - the chemical dissolving of soluble rocks such as limestone.)

(b) Characteristics of each section of a river valley:

(i) Upper course:

• Steep gradient and fast, turbulent flow.
• Narrow, deep V-shaped valley with vertical (downward) erosion dominant.
• Features such as waterfalls, rapids, gorges and interlocking spurs.
• Coarse, angular load and a small, swift channel.

(ii) Middle course:

• Gentler gradient and increased volume from tributaries.
• Valley widens; lateral (sideways) erosion becomes important.
• Development of meanders and a wider floodplain begins.
• Both erosion and deposition occur; load becomes finer.

(iii) Lower course:

• Very gentle gradient and slow, wide flow with large volume.
• Broad, flat floodplain with deposition dominant.
• Features such as large meanders, ox-bow lakes, levees, deltas and estuaries.
• Fine load (silt and mud) is carried and deposited.

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(a) Definition of climate

Climate is the average weather condition of a place observed and recorded over a long period, usually about 30 to 40 years.

(b) Influence of latitude on temperature

Temperature generally decreases from the Equator towards the poles. At low latitudes around the Equator, the Sun's rays are nearly vertical. They pass through a shorter distance of the atmosphere and their heat is concentrated on a small area; therefore, temperatures are high.

At higher latitudes towards the poles, the Sun's rays strike the Earth's surface obliquely. They pass through a greater thickness of atmosphere, where more heat is lost through scattering and absorption by clouds, water vapour and dust. The rays also spread over a larger surface area; therefore, temperatures are lower.

(c) Temperature at the 6,000 m mountain peak

Normal lapse rate = \(6.5^{\circ}\text{C}\) per 1,000 m ascent.

\[\text{Temperature decrease}=\frac{6.5}{1000}\times6000=39^{\circ}\text{C}\]

\[\text{Temperature at peak}=40^{\circ}\text{C}-39^{\circ}\text{C}=1^{\circ}\text{C}\]

Therefore, the temperature at the mountain peak is \(1^{\circ}\text{C}\).

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(a) What is a latitude? A latitude is an imaginary line drawn on the globe running from east to west, parallel to the Equator, measuring angular distance north or south of the Equator in degrees (0° at the Equator to 90° at the poles).

(b) Similarities between lines of longitude and latitude:

1. Both are imaginary lines drawn on the surface of the earth (they do not exist physically).
2. Both are measured in degrees (angular distance from a reference line).
3. Both are used together to fix or locate the position of places on the earth's surface.

(c) Ways in which lines of longitude differ from lines of latitude:

(Another difference: longitude is used to determine time/time zones, while latitude is used to determine climatic zones.)

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Chemically formed sedimentary rocks

(a) Mode of formation: Chemically formed sedimentary rocks are produced by chemical processes rather than the mechanical deposition of fragments. When water containing dissolved mineral salts evaporates, or when the water becomes saturated, the dissolved minerals are precipitated (deposited) out of solution. These precipitated minerals accumulate, settle in layers and are compacted and cemented to form solid rock. Examples of the processes include the evaporation of sea or lake water leaving behind salts, and the precipitation of calcium carbonate from lime-rich water in caves.

(b) Examples:

• Rock salt (halite) - from evaporation of salty water.
• Gypsum - from evaporation of sulphate-rich water.
• Some limestones and dolomite - from precipitation of calcium/magnesium carbonate.
• Stalactites and stalagmites and tufa - from precipitation of lime in caves.

(c) Importance:

1. Rock salt (halite) is used as table salt and as a raw material in the chemical industry.
2. Gypsum is used to manufacture plaster of Paris and cement.
3. Limestone is an important raw material for cement, and for building and glass making.
4. Some deposits store underground water and minerals, and limestone landscapes provide caves of tourist interest.

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Occurrence of drought

(a) Causes:

1. Prolonged failure or scarcity of rainfall over a long period.
2. Persistent dry, offshore winds (e.g. the dry, dust-laden North-East Trade Wind / harmattan) that bring no moisture.
3. Deforestation and removal of vegetation, which reduces evapotranspiration and rainfall.
4. Desert encroachment (desertification) and general climate change / global warming.

(b) Area affected: Drought mainly affects arid and semi-arid regions such as the Sahel zone of West Africa (e.g. northern Nigeria, Niger, Chad, Mali), the areas bordering the Sahara, and other dry margins in the Horn of Africa and southern Africa.

(c) Effects:

1. Crop failure and famine due to lack of water for farming, leading to hunger and malnutrition.
2. Death of livestock and loss of grazing land.
3. Drying up of rivers, wells and water bodies, causing acute water shortage.
4. Migration of people and animals, spread of desert conditions and conflict over scarce resources.

(d) Control:

1. Afforestation and shelter belts to check desert advance and improve rainfall.
2. Construction of dams, boreholes and irrigation schemes to store and supply water.
3. Drought-resistant crops and better land management (avoiding overgrazing and bush burning).
4. Public education and provision of relief and early-warning systems.