WAEC SSCE - Geography - 1993 (Essay)

Détails de la réponse

(a) Four factors that have encouraged the concentration of industries in the Lagos area

• Large market and population: Lagos is the most populous urban area in Nigeria, providing a big ready market for manufactured goods.
• Good port facilities: the harbours at Apapa and Tin Can Island ease the import of raw materials and machinery and the export of finished goods.
• Good transport network: Lagos is the hub of roads, railway and an international airport, linking it to the rest of the country and the world.
• Availability of labour: a large pool of both skilled and unskilled workers is present because of heavy migration to the city.
• Availability of capital and services: banks, insurance and head offices concentrate there, providing finance and business services; electricity and water supply are also relatively better.

(b) Significance of the concentration to the inhabitants

• Provision of employment and steady income for many people.
• Availability of a wide range of manufactured goods to buy locally.
• Growth of allied businesses and services (transport, trading, repairs), spreading wealth.
• Improvement of infrastructure such as roads, power and water in the area.
• However it also brings overcrowding, pollution and high cost of living, which the inhabitants must cope with.

Détails de la réponse

(a) Four ways lines of latitude differ from lines of longitude:

(Also acceptable: the spacing between parallels is roughly constant, while meridians are farthest apart at the Equator; latitude determines climate/temperature zones, longitude determines local time.)

(b) Time calculation:

Town A is at long \(75^{\circ}\text{W}\), Town B at long \(120^{\circ}\text{E}\). They are on opposite sides of the Prime Meridian, so add the longitudes:

\[ \text{Longitude difference} = 75^{\circ} + 120^{\circ} = 195^{\circ} \]

The Earth turns \(15^{\circ}\) in \(1\) hour, i.e. \(1^{\circ} = 4\) minutes:

\[ \text{Time difference} = 195 \times 4 = 780\text{ minutes} = 13\text{ hours} \]

Town B is east of Town A, so its time is ahead. Add 13 hours to A's time:

\[ 5:00\text{ p.m. Friday} + 13\text{ hours} = 6:00\text{ a.m. Saturday} \]

Time at Town B = 6:00 a.m. on Saturday.

Détails de la réponse

Reasons for any three of the following:

(a) Importance of fruit farming in the Mediterranean lands

• The hot, dry summers and mild, wet winters suit citrus, grapes, olives and figs.
• Long hours of bright sunshine ripen and sweeten the fruits.
• Deep-rooted fruit trees can reach underground water during the dry summer.
• Nearby industrial markets in Europe and good transport encourage commercial fruit growing.

(b) Predominance of lumbering in the Zaire basin

• The basin has a vast tropical rain forest with valuable hardwood trees (mahogany, ebony).
• Hot, wet equatorial climate gives continuous tree growth and quick regeneration.
• The many navigable rivers (Zaire and tributaries) provide cheap transport of logs.
• Low population and little farming leave the forest largely intact for exploitation.

(c) Declining importance of bush fallowing in West Africa

• Rapid population growth has increased pressure on land, so there is no longer enough land to leave fallow.
• Fallow periods have shortened, reducing soil recovery, so farmers turn to fertilisers and permanent cultivation.
• Introduction of modern farming (irrigation, mechanisation, cash crops) replaces the old shifting system.
• Urbanisation and land shortage make continuous cultivation necessary.

(d) Importance of plantation agriculture in East Africa

• The cool, fertile highlands with reliable rainfall suit cash crops such as tea, coffee and sisal.
• Large estates and available capital (partly from former colonial settlers) support big plantations.
• Cheap and abundant labour is available.
• Good demand and export outlets earn valuable foreign exchange.

Détails de la réponse

(a) What is soil?

Soil is the uppermost loose layer of the earth’s crust in which plants grow. It is made up of weathered rock particles (mineral matter), humus or organic matter, water, air and living organisms. It provides plants with support, water and nutrients.

(b) Process of soil formation

Soil formation is the gradual development of soil from parent rock and organic materials. The main process involved is weathering, together with the addition and decomposition of organic matter. Weathering is the breaking down of rocks into small particles by physical, chemical and biological agents.

The processes of weathering involved in soil formation are:

(i) Physical weathering:

This is the breaking down of rocks into smaller pieces without changing their chemical composition. It is caused by agents such as heating and cooling, running water, wind, ice, pressure and abrasion.

(ii) Chemical weathering:

This is the decomposition or breakdown of rocks through chemical changes in their minerals. It is caused by water, oxygen, carbon dioxide and weak acids. Chemical processes include solution, oxidation, carbonation, hydrolysis and hydration.

(iii) Biological weathering:

This is the breakdown of rocks by living organisms. Plant roots grow into cracks in rocks, while burrowing animals, earthworms, rodents and human activities help to break and loosen rock materials. Micro-organisms also decompose dead plants and animals to form humus.

As weathered rock particles mix with humus, water, air and living organisms over a long period, soil develops. Rainwater may wash fine particles and dissolved minerals from the upper layer to lower layers, leading to the formation of soil horizons.

(c) Soil profile

A soil profile is a vertical section or cut through the soil showing the arrangement of its different layers. These layers are called soil horizons. A typical well-developed soil profile has the following main horizons:

A Horizon (Topsoil):

This is the uppermost layer of soil. It is dark in colour because it contains humus formed from decomposed plant and animal remains. It contains many plant roots, insects, earthworms and micro-organisms. It is rich in nutrients and is the main layer in which crops grow. Fine clay particles and soluble minerals may be washed downward from this layer; therefore, it is also called the zone of leaching or eluviation.

B Horizon (Subsoil):

This is the layer below the A horizon. It contains less humus and fewer living organisms than the topsoil. Clay particles, iron compounds and minerals washed down from the A horizon accumulate here. It is therefore called the zone of accumulation or illuviation. It is usually lighter in colour than the A horizon and is relatively compact.

C Horizon (Parent-material horizon):

This layer consists mainly of partly weathered rock fragments and weathered debris. It contains little humus and few organisms. It is the source of the parent material from which the soil develops.

R Horizon (Bedrock):

This is the hard, solid and unweathered rock beneath the C horizon. It is the original parent rock from which the overlying soil materials are formed.

Détails de la réponse

(a) Two methods of farming as adopted in Nigeria (any two explained)

• (i) Mixed farming: the growing of crops and the rearing of livestock together on the same farm. The animals provide manure to fertilise the crops, and crop residues feed the animals, giving the farmer a steady income from both.
• (ii) Intensive farming: the cultivation of a small piece of land with heavy inputs of labour, fertiliser and improved seeds to obtain a high yield per unit area. It is common around densely settled areas and market gardens near towns.
• (iii) Plantation agriculture: the large-scale cultivation of a single cash crop (such as oil palm, rubber, cocoa or sugar cane) on a big, well-managed estate for sale and export, using scientific methods and hired labour.

(b) Three problems facing agriculture in Nigeria

• Use of crude, traditional tools and low level of mechanisation.
• Poor storage and processing facilities leading to heavy post-harvest losses.
• Inadequate capital and credit for farmers.
• Land tenure problems that limit large-scale farming.
• Pests, diseases and unreliable rainfall/drought.

(c) Ways these problems are being solved

• Provision of agricultural loans and credit through banks and government schemes.
• Supply of tractors, improved seeds, fertilisers and pesticides to farmers.
• Construction of dams and irrigation for dry-season farming.
• Building of silos and processing plants to reduce losses.
• Agricultural research and extension services to educate farmers, and land reform to ease access to land.

Détails de la réponse

(a) Three achievements of the Economic Community of West African States (ECOWAS)

• Introduction of the ECOWAS travel certificate/passport and removal of visa requirements, allowing free movement of member citizens within the region.
• Reduction and removal of tariffs on many goods through a trade liberalisation scheme, boosting inter-state trade.
• Establishment of a peace-keeping force (ECOMOG) that helped restore peace in member states such as Liberia and Sierra Leone.
• Cooperation in projects on roads, telecommunications and energy linking member states.

(b) Five problems facing ECOWAS

• Different official languages (English, French, Portuguese) hinder communication and unity.
• Similarity of products: members produce and export similar raw materials, so there is little to trade among them.
• Different currencies and lack of a common currency complicate trade and payments.
• Poor transport and communication links between member countries.
• Political instability, coups and border disputes among members.
• Loyalty to former colonial powers and outside trade partners weakens commitment to the community.

Détails de la réponse

(a) Four ways physical factors may hinder the development of road transportation (with examples):

• Rugged relief (mountains and steep slopes): highlands make road construction difficult and costly, requiring bends, cuttings and bridges, e.g. the Jos Plateau and the Cameroon Highlands.
• Swamps, marshes and flood plains: waterlogged, soft ground is hard to build on and roads are easily flooded, e.g. the Niger Delta mangrove swamps.
• Rivers and lakes: many wide rivers require expensive bridges or ferries and interrupt road routes, e.g. crossings over the Niger and Benue.
• Dense forest and adverse climate: thick tropical rainforest is difficult and expensive to clear, while heavy rainfall washes away and erodes roads (gullying), e.g. in the equatorial forest belt. (Deserts with shifting sand are also acceptable.)

(b) Four factors responsible for the poor railway network in tropical African countries:

• Shortage of capital: railways are very expensive to build and maintain, and poor countries cannot easily finance them.
• Difficult physical conditions: mountains, rivers, swamps and dense forest raise construction costs and limit routes.
• Colonial pattern of construction: existing lines were built mainly to link mines and cash-crop areas to the coastal ports for export, not to connect the interior, so the network is thin and unconnected.
• Low level of economic development and small traffic: sparse population, low industrial output and competition from road transport give too little freight and passenger traffic to justify new lines, and there is a shortage of skilled manpower and technology for maintenance.

Détails de la réponse

(a) Sketch map of West Africa

Key to the map

1. Home areas of ethnic groups:
   • Ashanti: south-central Ghana, around Kumasi.
   • Wolof: western Senegal, especially the Senegal River and Dakar hinterland.
   • Mandingo: the Upper Niger region, mainly Guinea and south-western Mali.
2. Areas with population density above 100 persons per km²:
   • South-eastern Nigeria, especially the Igbo heartland.
   • Southern Ghana, especially the Accra-Kumasi-coastal belt.
3. Areas with population density below 5 persons per km²:
   • Northern Mauritania.
   • Northern Mali and northern Niger, within the Sahara Desert.

(b) Factors aiding variation in population density in West Africa

1. Historical factors: Ancient towns such as Kano, Katsina and Timbuktu grew as centres of trans-Saharan trade. They attracted traders, craftsmen and administrators and consequently retained relatively large populations. Areas that formed capitals of old empires or enjoyed protection from warfare also became more densely settled. Conversely, slave raiding, wars and insecurity caused people to leave some areas, reducing their population density.
2. Agriculture: Fertile soils, reliable rainfall and good water supply encourage intensive farming and support many people. For example, parts of eastern Nigeria and the Ashanti area of Ghana have relatively high densities because food crops and cash crops can be grown successfully. Dry areas with infertile soils, sparse vegetation and unreliable rainfall, especially in the Sahara and Sahel, support little farming and therefore have sparse population.
3. Mining: Mineral deposits attract miners, investors and supporting services. Employment in gold-mining areas of Ghana, tin-mining areas of the Jos Plateau and other mineral fields attracts migrants. Mining settlements grow and local population density rises.
4. Industrialisation: Industries provide employment and stimulate the growth of trade, transport, housing, schools and health services. People therefore migrate to industrial and commercial centres such as Lagos, Accra, Kano and Dakar. This concentrates population in and around such towns, while areas with few industries remain less densely populated.

Détails de la réponse

(a) Four reasons why countries engage in world trade

• Uneven distribution of resources: No country has all it needs, so nations exchange what they have in surplus for what they lack.
• Differences in climate and relief: These allow different countries to produce different crops and goods, encouraging exchange (for example, temperate wheat for tropical cocoa).
• Differences in level of technology: Industrial nations sell manufactured goods to less-developed nations in exchange for raw materials.
• To earn foreign exchange: Countries export goods to earn money for development.
• Comparative cost advantage: Countries specialise in what they can produce most cheaply and import the rest.

(b) How these reasons have affected the volume of trade between Nigeria and her neighbours

• Nigeria and her neighbours (Niger, Chad, Benin, Cameroon) have similar climate and produce similar goods, so there is little to exchange, keeping the volume of trade low.
• All are developing economies exporting raw materials rather than manufactured goods, so they compete rather than complement one another.
• Where products differ (Nigerian manufactured/petroleum goods against livestock and grains from the Sahel neighbours), a modest but real cross-border trade exists.
• Weak transport links and different currencies further limit the volume of trade.

(c)(i) Two sea routes through which Nigeria trades

• The route across the Atlantic to Western Europe (via the Gulf of Guinea to ports in the United Kingdom and mainland Europe).
• The route across the Atlantic to North America (to the United States).

(ii) One export commodity through each route

• Route to Western Europe: crude petroleum (also cocoa).
• Route to North America: crude petroleum.

Détails de la réponse

As shown on the map above, the required inland drainage basin is the Lake Chad Basin, located in the north-eastern part of Nigeria.

(a) Locations and names on the map

• Inland drainage basin: Lake Chad Basin, in north-eastern Nigeria.
• Rivers flowing into the basin: Rivers Hadejia, Komadugu Yobe and Yedseram. Other acceptable examples include River Ngadda.
• Bight of Benin: on the south-western section of Nigeria’s Atlantic coast, west of the Niger Delta.
• Bight of Bonny: on the south-eastern section of Nigeria’s Atlantic coast, around the Niger Delta area.
• Idanre Hills: in south-western Nigeria, in Ondo State.
• Oban Hills: in south-eastern Nigeria, mainly in Cross River State near the Cameroon border.
• Biu Plateau: in north-eastern Nigeria, in Borno State.

(b) Reasons for the shallowness of the rivers and Lake Chad

• The Lake Chad Basin is an inland or closed drainage basin. Rivers flow into Lake Chad, but there is no major river flowing out of it to carry away water and deposited materials.
• Rivers entering the lake deposit large quantities of silt, sand, clay and other weathered materials. These materials gradually fill the river channels and the lake bed.
• The area has a hot, semi-arid climate; therefore, there is very high evaporation from the rivers and lake surface, reducing the volume and depth of water.
• Rainfall is generally low and seasonal, so many of the rivers have reduced flow during the dry season and cannot maintain deep channels.
• The land is generally flat and gently sloping, causing rivers to flow slowly and deposit rather than remove sediments.

(c) Benefits of Lake Chad

• Fishing: The lake provides fish and supports the livelihood of fishermen, fish traders and fish processors.
• Irrigation: Its water is used to irrigate crops, especially during the dry season.
• Water supply: The lake and its tributaries provide water for domestic uses, livestock watering and some industrial activities.
• Transport and trade: Parts of the lake and connecting waterways can be used for the movement of people, goods and local trade.
• Grazing and farming: Receding water leaves fertile alluvial soils which support floodplain farming and dry-season grazing.
• Employment: Fishing, farming, boat transport, trading and reed harvesting provide employment for people living around the lake.

Détails de la réponse

(a) Sketch map of Africa

Cape Verde here is the Cape Verde Peninsula on the coast of Senegal, near Dakar; it is not the Cape Verde islands. The following labelled sketch shows the required locations.

(b) Three economic importance of the highlands of Africa

1. Highlands force moist air to rise, cool and condense, causing relief rainfall. This provides water for farming and other human activities.
2. They contain valuable mineral deposits, which can be extracted by mining.
3. They are important sources of rivers. Water flowing from highland areas can be used for domestic supply, irrigation and hydro-electric power.

(c) Three importance of African rivers

1. Rivers can be dammed or used where there are rapids and waterfalls to generate hydro-electric power.
2. They provide water for domestic use, such as drinking and washing, and for industrial use.
3. They support fishing, providing food and employment for people living near rivers.

Examination reminder: For map questions, place each feature in its correct region as well as writing its name clearly. For “three ways” questions, give three separate, explained points rather than several uses combined into one point.

Détails de la réponse

(a) Distinction between internal trade and international trade

Internal (domestic) trade is the buying and selling of goods and services within the borders of one country, using one currency and free of customs duties. International trade is the exchange of goods and services between different countries, involving different currencies, foreign exchange, customs duties and international agreements.

(b) Four commodities of internal trade in Nigeria

• From the north: cattle (beef), and onions/grains such as millet and beans.
• From the south: palm oil, and kola nut (also plantain/yam and fish).

(c) Factors that promote trade between northern and southern Nigeria

• Difference in climate and vegetation gives the two regions different products, so they exchange what each lacks.
• Good transport links (roads and railways) connect north and south, easing the movement of goods.
• A common currency and common government remove barriers to exchange.
• Large population and demand create ready markets in both regions.
• Specialisation/division of labour between farming, herding and manufacturing zones.

(d) Limitations to internal trade in Nigeria

• Poor and inadequate transport in some areas, raising costs.
• Lack of storage and processing facilities, so perishable goods spoil.
• Insecurity and multiple illegal road tolls/checkpoints.
• Similarity of products in some areas reduces exchange.
• Fluctuating prices and inadequate market information.

Détails de la réponse

As shown on the outline map above, Nigeria may be divided into three broad soil and crop zones:

Soil characteristics favouring the crops

• Zone A, groundnut: The soils are generally loose, light and sandy, making them easy to cultivate and allowing the developing groundnut pods to penetrate the soil. They are well aerated and well drained, so water does not remain around the roots. The broad, gently sloping plains also favour extensive cultivation.
• Zone B, yam: The soils are mainly deep, fertile sandy loams. They are loose enough for yam tubers to enlarge easily, while still retaining adequate moisture. They are well drained and well aerated, reducing rotting of the tubers. Their acidity is low to moderate and they contain sufficient nutrients and organic matter for yam growth.
• Zone C, cocoa: The soils are deep, fertile forest soils with appreciable organic matter from decayed vegetation. They are usually clayey loams or loams that can retain moisture and nutrients. They are well drained, often on gently undulating land, which prevents waterlogging. The soils are also commonly slightly acidic, a condition suitable for cocoa.

Therefore, the sandy northern soils favour groundnut, the fertile well-drained sandy loams of the Middle Belt favour yam, and the deep, moist, organic-matter-rich forest soils of the south favour cocoa.

Détails de la réponse

(a) Three ways light industries differ from heavy industries

(b) Four reasons why light industries are more prevalent than heavy industries in Tropical Africa

• Shortage of capital: Light industries need less money to establish, which suits the limited local capital.
• Low level of technology and skilled manpower: Light industries use simpler machinery and less specialised labour.
• Availability of raw materials: Abundant agricultural raw materials favour agro-based light industries (food, textiles, beverages).
• Small and low-income market: The market mainly demands consumer goods, not heavy machinery, so light industries thrive.
• Inadequate power supply and infrastructure: Heavy industries need reliable, large-scale power and transport that many countries lack.

Détails de la réponse

Contrast between the Equatorial climate and the Tundra climate

In summary, the Equatorial climate is hot, wet and uniform with luxuriant forest, while the Tundra climate is cold, dry and highly seasonal with only low, hardy vegetation.

Détails de la réponse

(a) Account for the rapid growth of world population in the last two decades:

• Fall in the death rate due to improved medical care, vaccination, control of epidemics and better sanitation, so more people survive and live longer.
• High birth rate in many developing countries, where large families are still favoured and there is early marriage.
• Improved food supply and nutrition from better farming (irrigation, fertilisers, improved seeds), reducing famine and death from hunger.
• Better public health, clean water supply and hygiene, which cut infant mortality so more children survive to adulthood.
• Longer life expectancy and, in places, immigration, all adding to numbers.

(b) Three problems arising from this rapid growth:

• Pressure on food supply: population outstrips food production, causing shortages and malnutrition.
• Unemployment and poverty: too many people compete for too few jobs, lowering living standards.
• Pressure on services and environment: overcrowding, housing shortages, strain on schools, hospitals and water supply, and problems such as slums, congestion and pollution/deforestation.

(c) Suggested solutions:

• Family-planning and population-education programmes to reduce the birth rate.
• Increase food production and create more jobs by expanding agriculture, industry and skills training.
• Provide and expand social services and infrastructure (housing, schools, hospitals, water) and encourage even distribution of population and planned urban development.

Détails de la réponse

(a) Four components of the ecosystem:

• Producers (autotrophs): green plants that make food by photosynthesis.
• Consumers (heterotrophs): animals that feed on plants or other animals (herbivores, carnivores, omnivores).
• Decomposers: bacteria and fungi that break down dead organic matter.
• Abiotic (non-living) components: the physical environment, i.e. soil, water, air, sunlight and minerals.

(b) How the carbon cycle shows the interdependence of the components:

• Producers take in carbon dioxide from the air and, using sunlight, convert it during photosynthesis into carbohydrates, locking carbon into plant tissue.
• Consumers depend on producers: when animals eat plants (and other animals), the carbon passes along the food chain from one feeding level to the next.
• Respiration by both plants and animals releases carbon dioxide back into the air, returning carbon to the atmosphere.
• Decomposers break down dead plants and animals and their waste, releasing carbon dioxide (and enriching the soil), so carbon is recycled back to the atmosphere and to producers.
• The combustion of wood and fossil fuels also returns carbon to the air.

Thus carbon flows continuously between the abiotic environment, producers, consumers and decomposers, showing that each component depends on the others: producers supply food and remove \(\text{CO}_2\), consumers pass energy along, and decomposers and respiration return carbon so the cycle can continue.

Détails de la réponse

(a) Sketch map of Africa

Key to the sketch map

1. A: Congo Basin, an area receiving rainfall throughout the year.
2. B: Sudan savanna belt, an area receiving rainfall in summer only.
3. Warm current: Mozambique Current, flowing southwards along the south-east coast of Africa.
4. Cold current: Benguela Current, flowing northwards along the south-west coast of Africa.

(b)(i) Natural vegetation

Area	Type of natural vegetation
Congo Basin, rainfall throughout the year	Equatorial or tropical rain forest
Sudan savanna belt, summer rainfall	Savanna grassland

(b)(ii) Effect of rainfall on the vegetation

The Congo Basin receives heavy rainfall continuously throughout the year. There is no pronounced dry season, so moisture is available at all times. This supports a dense evergreen forest of tall broad-leaved trees arranged in layers, with a closed canopy.

In the Sudan savanna, rainfall is confined mainly to the summer months and is followed by a long dry season. The prolonged dry period prevents the growth of dense forest. Grasses predominate, while the scattered trees are drought-resistant and usually deciduous, shedding their leaves during the dry season to reduce water loss.

Détails de la réponse

(a) Relief of the ocean floor

(b) Characteristics of two features

Continental shelf

• It is the shallow, submerged extension of the continental landmass from the coast to the shelf break.
• It has a broad and gentle seaward slope and is usually less than about 200 m deep.
• It is covered mainly by sediments and is affected by wave action, erosion and deposition.
• Its shallow, well-lit water supports abundant plankton and marine life.

Ocean deep

• Ocean deeps are long, narrow and very deep depressions or trenches in the ocean floor.
• They form the deepest parts of the oceans, commonly exceeding 6,000 m in depth.
• They commonly occur near island arcs or continental margins and are associated with earth movements, earthquakes and volcanic activity.
• Fine deposits such as clay and oozes may accumulate on their floors.

(c) Economic importance of continental shelves

• They are important fishing grounds because sunlight penetrates the shallow water, encouraging the growth of plankton, which is food for fish.
• They provide employment and income in fishing, fish processing, boat building and related industries.
• They contain valuable mineral and energy resources, especially offshore petroleum and natural gas.
• They provide suitable locations for the development of ports, harbours and other coastal facilities.
• Sand, gravel and shells may be obtained from shelf deposits for construction and industrial uses.

Détails de la réponse

As shown in the diagrams above, the following are examples of landforms formed by river and wind action, and by earth movements.

(a) Ox-bow lake

An ox-bow lake is a crescent-shaped or horse-shoe-shaped lake formed on a river flood plain when a meander is cut off from the main river channel.

Characteristics

• It is a curved, crescent-shaped body of standing water.
• It occurs on the wide flood plain of a mature or old river, where the gradient is gentle.
• It is usually found beside the present river channel.
• It has no continuous connection with the main river, except possibly during floods.
• With time, it may become shallower through deposition of silt and may eventually dry up or become a swamp.

Mode of formation

1. A river flowing over a gentle gradient develops bends called meanders.
2. On the outer sides of the bends, the river flows faster and erodes laterally by hydraulic action and abrasion. This produces river cliffs.
3. On the inner sides of the bends, the water is slower and deposits sand and silt, forming slip-off slopes.
4. Continued lateral erosion narrows the neck of the meander.
5. During a period of flooding, the river cuts through the narrow neck and follows the shorter, straighter channel.
6. Deposition of alluvium seals both ends of the abandoned meander loop. The isolated loop remains as an ox-bow lake, as illustrated in the diagram.

(b) Zeugen

A zeugen is a table-like or ridge-like desert landform produced mainly by wind abrasion and differential erosion of alternating hard and soft rock layers.

Characteristics

• It occurs mainly in hot, dry desert regions where vegetation is sparse.
• It consists of a resistant layer of hard rock resting on a softer rock layer.
• It has a broad, relatively flat hard-rock cap and steep or undercut sides.
• Its lower soft-rock portion is more deeply eroded than the upper hard cap, giving it a pedestal or mushroom-like appearance in cross-section.
• Zeugen commonly occur as elongated ridges separated by grooves or furrows, often aligned with the direction of the prevailing wind.

Mode of formation

1. In a desert, horizontal or nearly horizontal beds of hard rock may overlie less resistant soft rock.
2. Intense heating and cooling cause the surface rocks to crack. These cracks and joints provide openings through which wind-blown sand can attack the rock.
3. Wind abrasion is strongest near the ground surface, where sand particles are carried by the wind.
4. The softer rock is worn away more rapidly along the cracks and weaker parts, forming furrows or trenches.
5. The resistant hard rock is eroded slowly and remains as a protective cap over the softer rock beneath it.
6. The remaining blocks stand out as ridges with hard tops and undercut soft bases. These are called zeugen, as shown in the diagram.

(c) Block mountain

A block mountain, also called a horst, is a large uplifted or relatively upstanding block of the earth's crust bounded by faults.

Characteristics

• It is a high, steep-sided mass of land.
• It is bounded by one or two major fault scarps.
• It is often long and narrow, with a fairly level or gently sloping summit.
• It may stand above lower down-faulted areas called grabens or rift valleys.
• Its sides are usually steep because they are formed by faulting rather than by ordinary erosion.

Mode of formation

1. Tensional forces within the earth's crust cause it to crack along two approximately parallel faults.
2. Movements occur along the fault planes.
3. The central block may be uplifted, or it may remain relatively stationary while the land on both sides subsides.
4. The central block then stands above the surrounding land.
5. The upstanding block is called a horst or block mountain, while the lowered blocks beside it may form grabens or rift valleys, as indicated in the diagram above.

Détails de la réponse

(a) Difference between urban and rural settlements:

(b) Four factors responsible for the increase in size of urban settlements:

• Rural-urban migration: people move to towns in search of jobs, higher wages and a better life.
• Industrialisation and commerce: the growth of factories, businesses and services attracts and holds a large workforce.
• Availability of social amenities: good schools, hospitals, water, electricity and entertainment pull people into towns.
• Natural increase: high birth rate over death rate within the town, plus administrative, educational and transport functions that draw more people.

(c) Four problems associated with such growth:

• Overcrowding and housing shortage, leading to the growth of slums.
• Unemployment and crime as jobs fail to match the rising population.
• Traffic congestion and pressure on transport.
• Pressure on services and environmental problems: strained water, power, schools and hospitals, poor sanitation, waste disposal and pollution.