The natural environment
Geology and topology
Zambia lies landlocked between the Tropic of Capricorn and the Equator, shaped like a giant butterfly and covering about 752,610km2. Most of this is part of the high, undulating plateau that forms the backbone of the African continent. Much of Zambia has an altitude of between 1,000m and 1,600m, whilst only a few of the low-lying rift valleys lie below 500m.
Zambia's oldest rocks, known as the Basement Complex, were laid down at an early stage in the pre-Cambrian era – as long as 2,000 million years ago. These were extensively eroded and covered by sediments which now form the Katanga system of rocks, dating from around 1,000 to 620 million years ago. These are what we now see near the surface in most of northeast and central Zambia, and they contain the important mineral deposits of the Copperbelt. Later still, from about 300 to 150 million years ago, the karoo system of sedimentary rocks was deposited: sandstones, mudstones, conglomerates and even coal. Towards the end of this era, molten rock seeped up through cracks in the crust, and covered areas of western Zambia in layers of basalt – the rock that is seen cut away by the Zambezi River in the gorges below Victoria Falls.
About 150 million years ago, during the Jurassic era of the dinosaurs, Africa was still part of Gondwana – a super-continent which included South America, India, Australasia and Antarctica. Since then Zambia's highlands have been eroded down from an original altitude of over 1,800m (Nyika Plateau is still at this altitude) to their present lower levels.
Very recently, perhaps only a few million years ago, the subcontinent had a dry phase. Then the sands from the Kalahari Desert blew far across southern Africa. Much of western Zambia now lies beneath a covering of Kalahari sand, as becomes abundantly clear the moment you try to drive in western Zambia.
Situated squarely in the tropics, Zambia gets a lot of strong sunlight, though the intense heat normally associated with the tropics is moderated in most places by the country's altitude and its rainfall.
Zambia's climate follows a similar pattern to that in most of southern Africa, with rainfall when the sun is near its zenith from November to April. The precise timing and duration of this is determined by the interplay of three air-streams: the moist 'Congo' air-mass, the northeastern monsoon winds, and the southeastern trade winds. The water-bearing air is the Congo air-mass, which normally brings rain when it moves south into Zambia from Central Africa. This means that the northern areas, around Lakes Tanganyika and Mweru, receive the first rainfall – often in late October or November. This belt of rain will then work south, arriving in southern Zambia by the end of November or the start of December.
As the sun's intensity reduces, the Congo air-mass moves back north, leaving southern Zambia dry by around late March, and the north by late April or May. Most areas receive their heaviest rainfall in January, though some of the most northern areas have two peaks: one in December and one in March. This twin-peak cycle is more characteristic of central and eastern Africa. The heaviest total rainfall is found in the north, and the lightest in the south.
Lusaka's climate statistics are typical of the pleasant climate found in the higher areas of southern and central Zambia:
The lower-lying valleys, including the Luangwa and Lower Zambezi, follow the same broad pattern but are considerably hotter throughout the year. In October, which is universally the hottest month, temperatures there often reach over 45°C in the shade.