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AN OVERVIEW OF THE PHYSICAL GEOGRAPHY OF AFRICA
PHYSICAL FEATURES
Africa straddles the equator, having an almost equal south and north extent. This division of Africa into almost two
equal parts (lengthwise) across the equator makes the climatic and physical conditions in the north repeat themselves
in the south. For example, the Kalahari Desert is the south's answer to the Sahara, while the conditions in the Cape
area are almost identical to those of the Mediterranean region.
Africa is the most tropical of all continents. Climate and vegetation range from equatorial rainforests, tropical
deserts and savanna grassland to Mediterranean. The Sahara Desert, the largest of its kind anywhere in the world, is
over 10.4 million km2 n North to south is approx. 1800 kms and east-west is 5600km.
GEOLOGY, RELIEF AND DRAINAGE
In terms of structure and relief features, Africa appears to be different from the other continents.. The continent is
made up of very old crystalline, metamorphic, and sedimentary rocks of great hardness. Africa's land mass is made
up of a simple tectonic plate. The continent has some extensive areas of faulted plateau. Only the Atlas Mountains in
the North and the Drakensburg mountains in the South are exceptions.
Most of the highlands and mountains are the result of recent volcanic activities mountains like the Kilimanjaro 19,340 ft (5895 m); Kenya 17,058 ft (5200 m); Meru -4569 m and Elgon 4053 m and in the Ethiopian highlands
Ras Dashen is about 15,000ft (4,573 m).
Lower average altitudes characterize most of the areas in the North. The Southern and Eastern areas have most of
the highest areas of the continent (900-1200m). The African plateau is underlain primarily by Precambrian rock that
dates back to more than 600 years.
The Rift Valley System (Fig 2.3 page 28)
A unique feature of Africa's physiography is its Y-shaped integrated Rift Valley system that is believed to have been
caused by the movement of the continental plates. The Rift Valley begins from the Red Sea and extends through the
Ethiopian highlands to the Lake Victorian region where it subdivides into an east and west segments and continues
southward through Lake Malawi to Mozambique. Its total length is estimated to be 6,000 miles (9,600 m). Average
width ranges between 20 miles (32 km) and 50 miles (80 km).
Rift Valley Lakes: The valley system has been occupied by elongated lakes lying within very deep trenches (Lakes
Tanganyika, 2133 feet (650 m) below sea level, Malawi, Turkana, Albert, Nyasa). Volcanic highlands and block
mountains (e.g. Ruwenzori massif 16, 404 feet, (5000 m) rises within the valley floor in places.
COASTLINE:
Africa’s coastline is generally straight and relatively short compared with that of other continents thereby resulting
in more harbors. The shape of Africa is relatively simple with a remarkably smooth outline. The rivers plunge off
the edges of the plateau into the sea in a series of falls and rapids. The coast is fringed with coral reefs, sand bars,
mangrove swamps and lagoons that block passage to the continents interior. The coastline of Africa is remarkably
straight. The narrow continental shelf is related to the steep face that the continent generally presents to the sea and
the faulting that has produced its general shape.
DRAINAGE
Some of the world's largest and longest rivers found in Africa, e.g the Nile, Zambezi, Congo and the Niger. The
rivers are not effective as transportation routes due to the existence of a large amount of rapids and cataracts. In
other continents the rivers offer the best entry into the interior from the coast the St. Lawrence and Mississippi and
also served as a cheaper means of transportation for industrial goods but this is not the case in Africa.
Despite being impediments to transportation, most of the rivers provide a great potential for the production of hydroelectricity. Indeed, Africa has the greatest potential than any of the other continent.
CLIMATE
Africa is the most tropical of all continents. Africa is the only continent that straddles the equator and therefore
incorporates both the Tropic of Cancer and Capricorn. The climate south of the equator mirrors that of the north of
the equator but the shape of the northern half of Africa reduces any maritime influence. This shape difference results
in a large desert, Sahara in the north and a much smaller one, Kalahari, in the south. The shape difference again
makes the southern portion of Africa cooler than the northern section of the continent, thereby making East Africa
more favorable for European settlement than West Africa. Archaeological studies and Satellite images show that the
climate of Africa has not always remained the same. Conditions that are more humid had once existed in the Sahara
desert and other drier parts of the continent.
Rainfall is the most significant climatic factor in Africa. Temperature is high through the continent because of the
continent’s location relative to Equator. Range of temperature is quite small and Wind is much less of a feature than
in temperate climates
Maritime versus Continental Climates
Large water bodies such as the Ocean and huge lakes modify climates in adjacent lands. In the continental interior,
where there are no large bodies of water, temperatures get VERY WARM in summer or during the day. Land is
solid so it heats up more rapidly during the day. The compact nature of the land means that only a thin surface gets
heated. As a result, heat absorbed into the thin layer of surface rocks is released very rapidly. The land surface is
therefore VERY COOL at nights and in winter. The interior location does not also allow rainfall to reach such
places thereby creating Warm, humid, hot and dry climates. These extremities in climate affect all states located in
the interior of continents. Such climates are called Continental Climates as against Maritime climates experienced
on lands located along coasts. In places such as Timbuktu, Mail, the diurnal and annual ranges in Temperature are
very high because of continentality.
Altitude
Since energy from the sun is transformed into heat on the surface of the earth, air temperature decreases with
altitude at an average rate of 3.5 o F per 1,000 feet (6.4 o C per 1000 meters) called the LAPSE RATE. Because of
this decrease of temperature with height, mountainous regions such as the Ethiopian highlands have very cool
temperatures. Very high peaks such as Mountain Kilimanjaro located along the equator even have permanent snow
cover. The combination effect of the above factors create variations in temperature, rainfall and other climatic factors resulting in the following climatic types.
1.
1.
Humid Equatorial Climates
2.
2.
Semi-arid climates
3.
3.
Desert Climate
4.
4.
Mountain climates
5.
5.
Humid Temperate climates
a.
a.
Cool summers
b.
b.
Dry summers and wet winters (Mediterranean)- Eastern South Africa and North Africa
c.
c.
Cool summers- Cape province in South Africa
VEGETATION & ECOLOGY OF AFRICA
Plant and animal life distribution and the different climatic/soil belts are closely related. Although some parts of the
continent retain their natural/virgin flora and fauna, increasing population and human activities seem to be
endangering these places. The Following types of vegetation types identified:
1. Tropical Rain forest:
This vegetation develops in low land areas with year-round precipitation. It extends throughout the Congo (Zaire)
basin and along the West coast of Africa with its widest in Sierra Leone. It is also found in a narrow belt along the
Southeastern coast south from the equator. Madagascar has a unique rain forest with special species of fauna and
flora not available on the main land. Generally, a heavy canopy of foliage with lianes and epiphytes characterizes
the rain forest. It occurs in regions where high temperatures are combined with heavy precipitation.
2. Temperate Forest:
This vegetation is poorly represented in Africa. It is only found on the lower slopes of the Ethiopian highlands and
elsewhere on the highlands of considerable elevation and rainfall
3. Mediterranean Woodland
These are evergreen trees and shrubs adapted to the hot dry season and mild wet season. In North West Africa, the
hilly belts support forests of evergreen oak, including cork oak and cedar, although they are now much reduced by
clearing and grazing. Evergreen shrubs with hard and usually small leaves are common as growth is slow but
continuous throughout the year. The vegetation in the Southwest corner is similar
4. Mangrove Swamps
This vegetation is found at the inter-tidal flats of the coastlines within the tropics.
5. Savanna or Tropical Grassland
The margin of the Savannah coincides with the rain forest belt where dry conditions begin. In such areas, there is
often a mosaic of forest savanna. Further away from the forest, as the dry season becomes more pronounced and
more prolonged, the Savannah woodland thins out, and trees that are more drought resistant are found. Generally,
the prevailing vegetation cover is grass interspersed with trees. In the zone of lower rainfall the huge baobab tree
illustrates storage of water while 'umbrella' trees show adaptation to dry wind. Acacias, some producing gum, are a
feature of the drier Sudan savanna. The Savanna extends with similar differences in character over the Lake plateau
across the Zambezi to the Drakensberg and dries towards the Kalahari in the thorny scrubs of the Bushveld. Major
crops produced in the Savanna: millet, sorghum, peanuts, and cotton.
6. Temperate Grassland or Veld
This is found in the veld areas of South Africa. Characterized by short grass and plants adapted to a brief growing
season but there are considerable differences due to altitude. It is by no means adapted everywhere to cultivation,
but maize, tobacco and temperate cereals are grown
7. Semi-desert and desert
Areas further north, the Savanna degenerate into semi-arid and then desert. This is the environment of the Sahel
ranging from thorn, wooded grassland to tussocky grasses with large bare patches of bare earth between. Human and
animals overpopulate the semi arid areas and both take their toll on the environment. As pasture is destroyed through
overgrazing and cultivation, the desert advances southward further restricting populations and increasing densities in
a vicious circle of desertification.