Search

Study region The Lakes Basin is located in the Main Ethiopian Rift. It covers the northern part of the rift valley basin, the Upper Awash River basin, and some sub-basins from the Omo River basin. Due to the presence of high fluoride (F−) content, natural contamination of groundwater has long been recognized as a water-related health issue in the area. Study focus A multidisciplinary research effort, including geological, hydrogeological, hydro-chemical, and geophysical investigations, was adopted to understand the 3D hydrogeological conceptual model and to evaluate F− enrichment in groundwater. New hydrological insights for the region The 3D hydrogeological conceptual model shows a complex hydrogeological environment and a clear hydraulic interconnection between different aquifers. The geological setting has deeply influenced the geometry of the aquifers, recharge and discharge areas, and F− enrichment in groundwater. Two hydrogeological units, namely sedimentary and volcanic multi-aquifers, were identified. The analyses of groundwater circulation, flow paths, and distribution of F- concentrations in each aquifer were conducted. In groundwater, the concentration of fluoride varies from 0.1 to 68.9 mg L−1; in surface water, it ranges from 0.6 to 244.2 mg L−1. Fluoride concentration of 62 % of the water samples analyzed exceeded the 1.5 mg L−1 WHO threshold for fluoride concentration in drinking water. The proposed methodological approach has been demonstrated to be a powerful tool that could be applied in other similar areas.

We present a geologic map of the Tekeze River basin that covers an area of ∼69,000 km2 of northern Ethiopia. The map synthesizes new data collected in two campaigns between March, 2012 and January, 2013 and compiled at a scale of 1:500,000 with published geologic surveys. The map focuses on the main geologic and tectonic features relevant to a modern interpretation of the geologic evolution of northern Ethiopia and as such, it represents an important synthesis for environmental and natural resource management.

An outlier consists of an area of younger rocks surrounded by older ones. Its formation is mainly related to the erosion of surrounding rocks which causes the interruption of the original continuity of the rocks. Because of its origin, an outlier is an important witness of the paleogeography of a region and, therefore, essential to understand its topographic and geological evolution. The Mekele Outlier (N Ethiopia) is characterized by poorly incised Mesozoic marine sediments and dolerites (∼2000 m in elevation), surrounded by strongly eroded Precambrian and Paleozoic rocks and Tertiary volcanic deposits in a context of a mantle supported topography. In the past, studies about the Mekele outlier focused mainly in the mere description of the stratigraphic and tectonic settings without taking into account the feedback between surface and deep processes in shaping such peculiar feature. In this study we present the geological and geomorphometric analyses of the Mekele Outlier taking into account the general topographic features (slope map, swath profiles, local relief), the river network and the principal tectonic lineaments of the outlier. The results trace the evolution of the study area as related not only to the mere erosion of the surrounding rocks but to a complex interaction between surface and deep processes where the lithology played a crucial role.

Recent studies highlight the importance of annual-scale dike-induced rifting episodes in developing normal faults and graben along the active axis of magmatic divergent plate boundaries (MDPB). However, the longer-term (102–105 years) role of diking on the cumulative surface deformation and evolution of MDPB is not yet well understood. To better understand the longer-term normal faults and graben along the axis of MDPB, we analyze fissure swarms in Iceland and Ethiopia. We first focus on the simplest case of immature fissure swarms, with single dike-fed eruptive fissures; these consist of a

Ethiopian basement formed between 850 and 450 Ma during the East African Orogen and represents the junction of the two distinct basement types found in Africa and Saudi Arabia: the low-grade Arabian-Nubian Shield and the high-grade Mozambique Belt. While many other localities along the East African Orogenic belt are well studied and despite the huge potential insight it could grant to the orogen’s evolution, Ethiopian Basement is poorly understood. This study aims to understand the tectonic evolution of the East African Orogen in Ethiopia through the examination of the age, origin, and evolution of previously unmapped syn- and post-tectonic plutons intruded into the Western Ethiopian Shield’s eastern edge. Dabana granite pluton crystallization ages were determined through U-Pb geochronological dating, and structural history was revealed through field mapping and thin section petrographic analysis. Whole rock elemental composition was determined through XRF (X-ray fluorescence) and ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) methods to investigate petrogenesis and chemical evolution of the plutonic rocks. Results indicate this pluton formed during three intrusive periods under distinct tectonic domains that represent an evolving convergent margin. The oldest granite dates to 797.6 Ma and is associated with hydrous melting during volcanic arc subduction, followed by post-subduction related anhydrous magmatism at 774.6 Ma. The youngest granites date to 635–639 Ma and are evidence of late-stage crustal thickening in the final stage of collision. Two metamorphic episodes are recorded in the structure and petrography, which formed gneiss during high-grade metamorphism at 775.22 Ma and low-grade deformation around 630 Ma. This study presents the first geochronological and geochemical data from plutonic rocks in the study area, and grants valuable insight into the dynamics and evolution of the East African Orogen in Ethiopia.

Like many other parts of Ethiopia, people in the Southern Nations, Nationalities and Peoples’ Region (SNNPR) do have indigenous knowledge on the preparation and use of traditional medicinal plants. Even though different studies have been conducted to document medicinal plants in different zones of SNNPR separately, there is no previous review work which summarizes the medicinal plants and the associated indigenous knowledge at the regional level (at SNNPR region as a whole or in large scale). Also, there is no previous review work that prioritizes the factors that affect medicinal plants at the regional level (including threatened medicinal plants). The purpose of this paper was to review habitat, growth forms, the method of remedy preparation and administration, marketability of medicinal plants, and to prioritize the factors that affect medicinal plants in SNNPR. Most of the medicinal plants in the majority of the reviewed areas are harvested from wild. Herbs are the most utilized life forms and leaves are the most utilized plant part in the preparation of remedies. Fresh plant materials are the most employed in the preparation of remedies. Majority of medicinal plants are not marketable. Agricultural land expansion is a major threat to medicinal plants which followed by deforestation. Olea europaea subsp. cuspidata, Prunus africana, Echinops kebericho, Croton macrostachys, Cordia africana and Dodonaea angustifolia, Hagenia abyssinica, Withania somnifera and Ficus spp are the highly affected medicinal plant species which require conservation and management priority in the region.

Lantana camara L. is one of the worst invasive alien species that are categorized worldwide. The objective of this review paper was to review the dispersal and threats posed by Lantana camara L. in Ethiopia and based on review results, to suggest management strategies that can bring solutions to the threats posed by the weed. Both biological characteristics of Lantana camara L. and its dispersal agents have contributed to the success of its dispersal. Even though Lantana camara L. is dispersed in other places within Ethiopia, Debrezeit, Dire Dawa, Harar and Somali are the hotspot areas for the weed. Biodiversity and potential agricultural loss, human and animal health problems and infestation in national parks are the identified threats that Lantana camara L. posed within the country. Utilization of Lantana camara L. for various purposes, prevention of its further dispersal into non-infected areas, use of fire, mechanical and biological control and awareness creation are the suggested management strategies that can bring solutions to the threats posed by the weed within the country.

The Main Ethiopian Rift (MER) is magmatically segmented and seismically active. The magmatic segments are arranged en echelon (e.g. Ebinger, C.J., Casey, M., 2001. Continental breakup in magmatic provinces: An Ethiopian example. Geology Society of America Bulletin, vol. 12, pp. 527–530). Furthermore they are about 50 km long and up to 20 km wide, orientated about N10°–20°E, and are therefore oblique to the main direction of Mid-Miocene border faults (N35°E). In this paper we propose that these segments not only represent magmatic but also tectonic segmentation. We use the association of the high spectral resolution of Landsat data (principal component analysis and classifications) and the very high spatial resolution of digitized aerial photographs to characterize and quantify the deformation along the rift. Additionally, several digital elevation models of metric resolution have been produced at different locations along the segments in order to quantify and describe the faulting. We define 4 tecto-magmatic segments (Gedemsa, Bosetti, Kone and Fantale), 40–70 km, 10–15 wide, arranged en echelon and N10°–20°E orientated. Each tecto-magmatic segment (TMS) is separated by 2–18 km wide domains exhibiting minor deformation. Furthermore, the TMS overlap in a N–S direction and show similar symmetrical deformation patterns. Within an individual segment deformation varies from its centre, where it is essentially magmatic, to its tips, where brittle deformation is predominant. The largest volumes of recent basalt are erupted in the centres and nearby. In contrast, recent magma injections are absent in the tip domains. It seems probable that dikes connect laterally to, and are fed by, the magmatic centres. Dikes are sub-parallel to the segment axis and therefore orientated normal to the recent extension direction. Within the TMS, aligned cones, atypical fault geometries, en echelon fault segments, and atypical displacement–length ratios all suggest that faulting is dike-induced. Along axis propagation of the TMS generate interactions between younger (Quaternary) intra-rift faults and older (Mid-Miocene) border faults. Thus, at the deformed tips, cross-cutting and long curved faults are produced. The fault interactions in the MER confirm that the border faults have been inactive during the recent stage of rifting. We discuss the implications of oblique rifting with moderate obliquity (α = 27°, angle between the extension direction and the trend perpendicular to the rift) at slow extension rates on active rifting processes associated with intermediate continental crust. The tecto-magmatic segmentation mirrors crustal segmentation beneath the rift axis, as indicated from 3-D-tomography (Daly, E., Keir, D., Ebinger, C., Stuart, G., Ayele, A., Waltham, D., 2007. Crustal structure of the northern Main Ethiopian Rift from a tomographic inversion of local earthquakes. Geophysical Journal International, in press; Keranen, K., Klemperer, S.L., Gloaguen, R., EAGLE Working Group, 2004. Three-dimensional seismic imaging of a protoridge axis in the Main Ethiopian rift. Geology 32 (11), 949–952). These long and narrow zones (40–70 km long and 10–15 km wide), where deformation is generated principally by diking and is associated with magmatic centres, have similarities with along-axis segmentation at mid ocean ridges. Consequently, deformation distribution and type in the MER can be considered the outcome of a transition between continental and active oceanic rifting.

Four major fault systems oriented N–S to NNE–SSW, NE–SW, E–W and NW–SE are identified from Landsat Thematic Mapper (TM) images and a high resolution digital elevation model (DEM) over the Ethiopian Rift Valley and the surrounding plateaus. Most of these faults are the result of Cenozoic - extensional reactivation of pre-existing basement structures. These faults interacted with each other at different geological times under different geodynamic conditions. The Cenozoic interaction under an extensional tectonic regime is the major cause of the actual volcano-tectonic landscape in Ethiopia. The Wonji Fault Belt (WFB), which comprises the N–S to NNE–SSW striking rift floor faults, displays peculiar propagation patterns mainly due to interaction with the other fault systems and the influence of underlying basement structures. The commonly observed patterns are: curvilinear oblique-slip faults forming lip-horsts, sinusoidal faults, intersecting faults and locally splaying faults at their ends. Fault-related open structures such as tail-cracks, releasing bends and extensional relay zones and fault intersections have served as principal eruption sites for monogenetic Plio-Quaternary volcanoes in the Main Ethiopian Rift (MER).

Deformation and magmatism within the ∼90 km wide northern Ethiopian Rift system is concentrated along a narrow zone - the Wonji Fault Belt. Two key areas (the Nazret-Dera and Asela-Ziway areas), located along the eastern margin of the north-northeast to northeast trending Main Ethiopian Rift, have been investigated in order to reconstruct the recent tectonomagmatic evolution of the northern branch of the Main Ethiopian Rift. In these areas, Early Pleistocene volcanic products (Wonji Group) overlie Pliocene volcanic rocks (Eastern Margin Unit). Detailed stratigraphical reconstructions have revealed the presence of several tectonomagmatic units which can be correlated between the two study areas. The stratigraphical and petrological study of these units outlined (1) the bimodal composition (basalts-pantellerites) of the oldest and youngest units and the unimodal character (pantellerites) of the products erupted during the intervening period; (2) the mainly fissural origin of the ignimbrites and oldest basalts; and (3) a mafic/felsic volumetric ratio of 1:5. The geological data suggest that, around the Pliocene-Quaternary boundary, a change in the stress field occurred in this Main Ethiopian Rift sector, passing from a direction of extension roughly orthogonal to the rift shoulders, to oblique rifting related to an east-west trending extension. In this framework the change in the style of volcanism observed in the Nazret-Dera and Asela-Ziway areas can be related to the change of the stress field. A new geodynamic model is presented for the Late Pliocene to Recent evolution of this sector of the Main Ethiopian Rift. According to this model, a large volume of rhyolitic products was erupted during an oblique rifting phase, following a previous period of pure extension. The change in the tectonic regime favoured partial melting of the underplated basalts as a decrease in the pressure and an elevation of isotherms occurred.

[1] The Red Sea and Aden rifts (or propagators) meet in Afar. Here we use remote sensing and field analyses to define the geology and structure of the southern part of the Red Sea propagator in Central Afar. This consists of the NW-SE trending Tendaho Graben (TG) and the younger and active NW-SE trending Manda Hararo Rift (MHR), partly within TG. Tectonic and volcanic activity within TG developed mostly between ∼1.8 and ∼0.6 Ma, with a stretching factor β ∼ 1.1, an extension rate ∼3.6 mm/yr and the fissural eruption of part (∼7000 km3/Ma) of the Afar Stratoid sequence (mainly basaltic lava flows and ignimbrites). MHR, before terminating southward, has a β ∼ 1.04 and an extension rate ∼1.2 mm/yr, and is associated with the emission of ∼600 km3/Ma of basalts in the last ∼0.2 Ma. These data suggest that after the exceptional amount of magma erupted between ∼1.8 and ∼0.6 Ma, magmatic and tectonic activity significantly decreased along the southern part of the Red Sea propagator in the last ∼0.2 Ma. This decrease coincides with the on-land development and migration of the more active (inferred extension rate in the order of ∼10 mm/yr, as proposed in previous studies) Aden propagator, suggesting that spreading in Central Afar mainly occurred along one active propagator at any one time.

This paper presents a detailed geomorphological overview of the landforms and processes characterizing the Dessie basin, a small graben located on the western Afar Margin (Ethiopia), which is a physiographic province characterized by small, closed basins and mountain ranges produced by regional extension. Large-scale geomorphological survey and mapping of the basin allowed to point out the noteworthy morphodynamic role of the present-day slope processes, including numerous landslides of different typology and size. These processes heavily interact with the built-up area of Dessie town, one of the most important cities of Ethiopia with ca. 200,000 inhabitants, which occupies a large part of the basin floor. The potential incidence of landslides of different typology in the basin and their possible impact on the urban settlement are put in relation with the distribution of the different landform units which make up the basin surface.

The Main Ethiopian Rift (MER) is associated with bimodal Quaternary magmatism. Field, remote sensing, and geochronology data are used to examine the relationships between axial acidic volcanoes and basaltic eruptions. Two main Quaternary magmatic episodes are recognizeable in MER: a) basaltic flows followed by ignimbrites and silicic centers in the rift floor (2-1 Ma) and b) axial silicic volcanoes and basalts since ~650 Ka. The first episode consists mainly of basaltic flows related to the Afar Stratoid and outcrops in the central and northern MER. Scattered silicic centers developed subsequently along the rift floor. In the second episode, spatial and temporal correlation between rift localization and silicic centers becomes more evident. The silicic centers are located at the intersection of the WFB with earlier structures, especially E-W faults. With ageing, these centers become faulted and allow basalts to erupt right through the volcanic edifice, suggesting a decrease in the amount of differentiation in the magma chambers, possibly due to their cooling. This style of evolution appears to be characteristic of continental rifts prior to the onset of drifting.