The effect of hydrogeological and hydrochemical dynamics on landslide triggering in the central highlands of Ethiopia | L’ effet des dynamiques hydrogéologique et hydrochimique sur le déclenchement des glissements de terrain sur les hauts plateaux du centre de l’Ethiopie El efecto de la dinámica hidrogeológica e hidroquímica en el desencadenamiento de los deslizamientos de tierra en las montañas centrales de Etiopía 水文地质和水化学动力条件对埃塞俄比亚中部高地诱发滑坡的影响 O efeito da dinâmica hidrogeológica e hidroquímica no desencadeamento de deslizamento de terra nos planaltos centrais da Etiópia
2021
Mebrahtu, Tesfay Kiros | Banning, Andre | Girmay, Ermias Hagos | Wohnlich, Stefan
The volcanic terrain at the western margin of the Main Ethiopian Rift in the Debre Sina area is known for its slope stability problems. This report describes research on the effects of the hydrogeological and hydrochemical dynamics on landslide triggering by using converging evidence from geological, geomorphological, geophysical, hydrogeochemical and isotopic investigations. The chemical characterization indicates that shallow to intermediate aquifers cause groundwater flow into the landslide mass, influencing long-term groundwater-level fluctuations underneath the landslide and, as a consequence, its stability. The low content of total dissolved solids and the bicarbonate types (Ca–Mg–HCO₃ and Ca–HCO₃) of the groundwater, and the dominantly depleted isotopic signature, indicate a fast groundwater flow regime that receives a high amount of precipitation. The main causes of the landslide are the steep slope topography and the pressure formed during precipitation, which leads to an increased weight of the loose and weathered materials. The geophysical data indicate that the area is covered by unconsolidated sediments and highly decomposed and weak volcanic rocks, which are susceptible to sliding when they get moist. The heterogeneity of the geological materials and the presence of impermeable layers embodied within the highly permeable volcanic rocks can result in the build-up of hydrostatic pressure at their interface, which can trigger landslides. Intense fracturing in the tilted basalt and ignimbrite beds can also accelerate infiltration of water, resulting to the build-up of high hydrostatic pressure causing low effective normal stress in the rock mass, giving rise to landslides.
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