Abstract
Abstract. The Main Ethiopian Rift (MER), where active continental rifting creates specific conditions for landslide formation, provides a prospective area to study the influence of tectonics, lithology, geomorphology, and climate on landslide formation. New structural and morphotectonic data from central Main Ethiopian Rift (CMER) and southern Main Ethiopian Rift (SMER) support a model of progressive change in the regional extension from NW–SE to the recent E(ENE)–W(WSW) direction, driven by the African and Somali plates moving apart with the presumed contribution of the NNE(NE)–SSW(SW) extension controlled by the Arabian Plate. The formation and polyphase reactivation of faults in the changing regional stress field significantly increase the rocks' tectonic anisotropy, slope, and the risk of slope instabilities forming. According to geostatistical analysis, areas prone to landslides in the central and southern MER occur on steep slopes, almost exclusively formed on active normal fault escarpments. Landslide areas are also influenced by higher annual precipitation, precipitation seasonality, vegetation density, and seasonality. Deforestation is also an important predisposition because rockfalls and landslide areas typically occur on areas with bushland, grassland, and cultivated land cover. A detailed study on active rift escarpment in the Arba Minch area revealed similar affinities as in a regional study of MER. Landslides here are closely associated with steep, mostly faulted, slopes and a higher density of vegetation. Active faulting forming steep slopes is the main predisposition for landslide formation here, and the main triggers are seismicity and seasonal precipitation. The Mejo area situated on the uplifting Ethiopian Plateau 60 km east of the Great Rift Valley shows that landslide occurrence is strongly influenced by steep erosional slopes and a deeply weathered Proterozoic metamorphic basement. Regional uplift, accompanied by rapid headward erosion forming steep slopes together with unfavourable lithological conditions, is the main predisposition for landslide formation; the main triggers here are intense precipitation and higher precipitation seasonality.
Highlights
Slope instabilities, including mainly landslides, rockfalls, and debris flows are usually influenced by key factors such as slope, bedrock lithology and rock fabric anisotropy, active tectonics and seismicity, type and grade of weathering, climatic conditions, vegetation cover, land use, and human activity
Active continental rifting has a distinct effect on the formation of landslides
The formation, superposition, and polyphase reactivation of fault structures in the changing regional stress field increase the tectonic anisotropy of rocks and increase the risk of slope instabilities forming
Summary
Slope instabilities, including mainly landslides, rockfalls, and debris flows are usually influenced by key factors such as slope, bedrock lithology and rock fabric anisotropy, active tectonics and seismicity, type and grade of weathering, climatic conditions, vegetation cover, land use, and human activity. Links between these factors and the formation of landslides and rockfalls are complex Other studies conclude that lithology and precipitation are the main landslide controlling factors (e.g. Kumar et al, 2019, and references therein)
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