Relief and drainage of africa

TOPIC: RELIEF AND DRAINAGE OF AFRICA

PHYSICAL FEATURES OF AFRICA

Africa as a whole is simply a vast plateau of ancient rocks with a narrow coastal plain. The plateau has an average height of about 425m in the north and west, while the southern and eastern parts of the continent have an average height of over 900m. above the general levels of the plateau are outstanding rideges and surfaces. In the north are the Ahaggar, Tasilli, Tibesti, and Darfur plateaux. Other examples include the Fouta Jallon and Guinea highlands (900m high) in West Africa. These granitic upland broke the monotony of the plateau.

In some areas, mostly in East Africa, volcanism has helped in building peaks high above the general level of the plateax. Examples of these include, Cameroon mountain (4,070m), the Ethiopian highlands(over 3500m), the Elgon (4321m), Kenyan mountains (5199m) and the Kilmanjaro (5898m), which is the highest peak in Africa.

Folding, although not so pronounced in Africa as in Europe, left some marks on the continent of Africa. In the extreme northwest, folding gave rise to the Atlas mountain ranges. The origin of this range is traced to the folding which occurs in the Alps of Europe.

Folded mountains are also restricted to the extreme part of South Africa. Examples include the Cape range made up of Zwarte, Bergen, Lange Bergen and Oilfants mountains popularly referred to as Drakensberg highlands.

VALLEYS

A striking feature of Africa’s relief is the Great Rift Valley of East Africa. This huge trough, about 5000km long, beings from the Jordan valley and runs southwards through the Red Sea. It then passes through Ethiopia and terminates at lake Malawi, from where a western trough is a result of down-warping of the land between two parallel faults. The East Africa Rift Valley contains a number of long, narrow and deep lakes such as Lake Tanganyika, the world second deepest lake (1435m). Other lakes include Lake Albert, and Lake Edward. Often the course of Rift Valley is traced by strings of lakes.

MAP OF AFRICA SHOWING RIVERS, LAKES AND DRAINAGE SYSTEMS

DRAINAGE

The drainage system of the African continent is a reflection of its plateau character. The great plateau which slopes northwards as far as the Equator is deeply cut into by the basins of the River Congo, River Nile, and the Lake Chad. The basins are separated by plateau such as, the Cameroon mountains in the western limb, the Tibeste, Darfur, Tassile and Ahaggar Plateaux in the central limb and the Ethiopian highlands in the Eastern limb. This result in large parts of Africa being areas of inland drainages. These include:

1. The Chad – Bodele depression in the north, receiving the Shari river and others.

1. The Ngami-Makariki depression in the south receiving Okavango and its tributaries

• The Bangwieolo depression in Zambia

In addition of these inland drainages are large areas of inland deltas and swamps. They include:

1. The saucer – shaped Congo basin

1. The inland delta of the middle Niger which in the past was an inland lake but was drained by a river capture by the lower Niger.

1. The Bhar el Ghazel section of the middle Nile

1. Extensive flooded areas around the Lake kioga on the Nile, between Lake Victoria and Lake Albert

RIVERS

Africa continent is drained by the following Rivers; the Nile 6400km (the longest River in the world), Congo 4,800km, the Niger 4,060km, the Zambesi 2400km, the Orange, 1.920km, the Orange, Gambia and Volta flow into the Atlantic ocean. The Zambesi and Limpopo flow into the Indian Ocean, while the Nile empties into the Mediterranean Sea.

CHARACTERISTICS OF AFRICAN RIVES

1. They have rapids and waterfalls where they descend the steep slopes of the plateau

1. They are characterized by seasonal flowing as a result of marked wet and dry seasons

• Most of the Rivers are not navigable due to the presence of rapids, waterfalls, sand bars or deltas

1. They contain water weeds which limits river transportation

LAKES

Lakes in Africa are of three main types. They are as follows:

1. Lakes: Caused by gentle warping of the surface. Examples include Lake Victoria, Chad, Kioga, Okavango, Makarika and Etosha pan. They are identified from other lakes by their broad and shallow nature

• Reft valley Lakes: Include, Lakes Tanganyika, Malawi, Turkana, Kivu, Edward and Albert. They are identified by their Long, narrow and deep character

1. Man-made Lakes: they owe their origin from the damming of rivers for hydroelectric power. Examples are lake Volta on the River Volta in Ghana, Kaninji Lake on the River Niger and Lake Kariba on the Zambesi River

IMPORTANT OF RIVERS AND LAKES IN AFRICA

1. They provide water for domestic uses (washing, cooking and drinking)

1. They provide water for industrial uses. For example, for washing and cooling engines. It is also an important raw material in breweries and soft drink bottling companies

• They provide water for irrigation

1. Rivers, such as the Nile, Volta and Zambesi, are used in generating hydroelectric power

1. Rivers and lakes provide fishing grounds. The fishes in turn provide valuable protein for the people

1. They provide a means of transporting people, goods and services, thus promoting internal trade.

• Some rivers and lakes serve as tourist centres which may generate revenue

THE COASTLINE OF AFRICA

The African continent is characterized by a narrow coasting with a few deep indentations. As a result, there few good natural harbours. Instead of penetrating estuaries, some of the rivers have their mouths blocked by sandbar and shallow lagoons, thereby obstructing navigation. The coastline lacks deep fiords, gulf sand bays.

The coastline of africa can be classified as follows:

1. Smooth sandy coast e.g., between Cape Blanc in Mauritania and Dakar in Senegal

1. Ria or drowned coast: Example is found between Dakar and Shebro Island covering the coast of Sierra Leone, Guinea and Guinea Bissau

• Cliff coast – Is found between Liberia and Ghana

1. Lagoon coast – Common along the eastern coast of Cote d’Ivoire, Togo and Western Nigeria e.g., Lagos Lagoon, in Nigeria and Porto Novo Lagoon, In Benin Republic

1. Delta coast, Niger-Delta and Nile Delta are good examples

1. Coast with spit formed by drift are common along the coast of Nambia and the coast of Mozambique

• Coral reef coast: Found along the shores of the Red Sea, Somalia, Kenya, Tanzania and Mozambique

EXERCISES

1. Described the physical geography of Africa under the following:

(a) Size (b) Position and location and (c) Political divisions

2. Explain the main features of the morphology of African coastlines
3. Outline the principal categories of African lakes and briefly discuss their geological history

4. In what ways are African rivers important to man?