Historical soil erosion in the West Usambara Mountains, Tanzania. A study based on hillslope deposits.

Abstract

Modern soil erosion triggered by anthropogenic forcing is a well studied phenomenon, but few studies focus on erosion on a longer timescale, forced by climatic changes. A better understanding of the way these long term climatic forcings act on soil erosion is needed to prepare ourselves for the future. Colluvial deposits form valuable archives of the past erosion on a hillslope. The West Usambara Mountains in Tanzania form an ideal location for research on the past erosion, since they are subjected to severe erosion, of which the present day part is well studied and documented. In this study, colluvial stratigraphies are interpreted and dated by OSL in order to reconstruct the geomorphic response of the landscape to past environmental changes, caused by both natural and anthropogenic forcings. The colluvial records, showing unstable periods with erosion alternated with stable periods of pedogenesis, can be linked successfully to the past climatic and anthropogenic history of the area. A reconstruction of the erosion history from the last three centuries is created, based on the information found in the colluvial deposits. This research proves that colluvium stratigraphies have a high potential for holding valuable sedimentary archives of the past erosion and environmental history. When interpreted and dated correctly, colluvial deposits can be used successfully to reconstruct the erosional history of an area.