Introducing the highlands and escarpments of Angola and Namibia

Abstract

Our paper outlines the key features that characterise and define the highlands and escarpments of Angola and Namibia (HEAN) and their topography, origins, drainage, landscapes, soils and climate. The highlands and escarpments stretch some 2,700 km from Cabinda and the Congo River southwards to the Orange River on Namibia’s border with South Africa. Two plateaus above 1,700 masl cover large areas: the Angolan Planalto and Namibia’s Khomas Hochland. Numerous inselbergs rise above the landscape, and many scarps form sharp margins between lower, western and higher, eastern areas. The highest peaks rise above 2,500 masl. As part of the Great Escarpment along the margins of southern and stretches of eastern Africa, the HEAN probably rose isostatically as the erosion of coastal crust reduced the mass of coastal Africa following the breakup of Gondwana. Three groups of rivers are associated with the HEAN: erosive rivers that flow rapidly off the highlands westwards to the coast; rivers that flow north or southwards, hugging the eastern flanks of the highlands until they turn west towards the coast; and rivers that flow eastwards and away from the highlands. Rivers in the northern third of the HEAN have perennial flows, those in the central third are ephemeral, and those in the southern third seldom carry water. The 11 landscape units defined in the HEAN are differentiated based on their topographical, geomorphological, ecological and climatic characteristics. Cambisols, Ferralsols, Leptosols and four other soils cover over 99% of the area. Most soils have limited plant nutrients, organic carbon and water-holding capacity. Average annual rainfall ranges from about 1,200 mm in the north of Angola and on the Angolan Planalto to less than 100 mm in the far south of Namibia. Rainfall is most variable in the southern and western areas. There are two peaks of rainfall in the northern half of Angola: in November and December and then in March and April. Within the HEAN, the southern areas are far more arid than those in the north because of the combined effects of high evapotranspiration and low rainfall.