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Geological, historical and present-day erosion and colluviation in Lesotho, southern Africa


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Authors

Singh, Meena Vasi 

Abstract

Thick colluvial deposits, sometimes reaching a thickness of 10 metres, cover the lowlands of Lesotho. Gully erosion whilst removing the colluvial storages, and resulting in the degradation of the landscape, provides an opportunity to examine colluvial profiles. A genesis for the colluvium is sought in an attempt to understand the conditions of formation, and hence a reconstruction of past environments. The link between colluviation and gullying is examined. The research aims at reaching an understanding of erosion processes over varying timescales and spatial boundaries. Contradictory and often sparse data exists about environmental change in southern Africa. An hypothesis proposed, is that processes of erosion have changed, as the location of erodible sediment has been transferred from the steep slopes (where sheet wash removed soils) and deposited as colluvium on the footslopes and valley bottoms (where gully erosion is incising the colluvium). Hence erosion, is believed to have occurred throughout the geological and historical period. This study has shown that gully erosion which is frequently attributed to land management, is a continuation of a geological process. The effects of climatic factors and intrinsic thresholds controlling the rate and nature of removal processes are assessed. Historical soil erosion has been documented using a wide range of sources ranging from colonial and administrative reports, memoirs and diaries of missionaries, sketches and drawings, to oral history. An examination of traditional Basuto agricultural practices suggests sensitivity to the fragile, semi-arid environment. Recent erosion has been monitored in the field and valuable information gained through interviews with rural women in the field. The change from traditional, subsistence agriculture to a market-oriented agricultural economy led to the disappearance of indigenous conservation practices, as increased output became a priority. Gully expansion in turn, documented since the end of last century, has been destructive to agriculture and poses a threat to fields of cultivated food, and therefore to the livelihood of thousands of people.

Description

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Date

1994-08

Advisors

Richards, Keith

Keywords

Lesotho, erosion, colluviation, gullies, agriculture

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge