Highlands in East Africa: Unstable slopes, unstable environments?

Mass movements are geomorphic processes affecting steeplands all over the world. Mass movement research is comprehensive, but has been concerned mainly with temperate and periglacial areas, while tropical steeplands are still inadequately covered. This paper summarizes research on mass movements carried out since the early 1990s in Nyandarua Range, Kenya and Uluguru Mountains, Tanzania. Research aspects include processes and causes, aspects of scar recovery, and effects on landscape morphology in a long-term perspective. It is argued that mass movement is the most common denuding agent in the highlands and that natural prerequisites for movement are ample, being of overruling importance in comparison to human-induced movement. Landforms imply that mass movement has been paramount in long-term landscape sculpturing. Recovery of landslide scars is surprisingly fast. In Uluguru Mountains, scars are brought back to agricultural production within about 20 years; in Nyandarua Range considerable physical and chemical recovery of scar topsoil has taken place within 10 years. Hence, land degradation by mass movement is of transient character.