Africa south of the Sahara is roughly three times the size of the continental United States. The northern edge of the region borders the massive Sahara. The Atlantic and Indian Oceans surround the rest of the continent. The annual rainfall rate for this region varies from more than 60 inches in the tropical rain forests near the Equator to less than 4 inches in the semiarid steppe climate.
The Land Africa's overall elevation is higher than that of any other continent. High plateaus cover the continents, rising in elevation from the coast inland and from west to east. Volcanic mountains, such as Kilimanjaro, are located in the Eastern Highlands. Shifting tectonic plates formed the Great Rift Valley, which runs from Syria to Mozambique. Most of the region's lakes are near the Great Rift Valley. The region's great rivers originate in the high plateaus and descend toward the sea. Sharp escarpments and steeps cataracts make navigation impossible on parts of these rivers. Africa south of the Sahara is rich in natural resources, including oil, gold, uranium, and diamonds. Because of irregular and unpredictable rainfall, irrigation and harnessing hydroelectric power are difficult.
Climate and Vegetation Near the Equator, orchids and ferns grow amid the canopy of trees that tower up to 150 feet above the floor of the tropical rain forests. Tropical grasslands, known as savanna, cover nearly half of the continent. Tornadoes sometimes occur there when northeastern winds, called harmattans, collide with humid air blown in from monsoons. Further north and south of the savannas are drier steppe climates with low-growing grasses and acacia trees. Grasses and trees can even be found in isolated deserts, such as the Kalahari in southern Africa, where little rain falls.