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Two new rock art sites in Irob district of eastern Tigrai, northern Ethiopia, are presented. One of the sites, Ra Bolo, contains images of domestic cattle and human figures while the other, Adhay Bolo, appears to contain only images of caprines, the only example of such a scene not just in the region but in all of Ethiopia. The sites fit well with the already established northern Ethiopian assemblage of paintings and engravings. The paintings belong to the earliest phase of Ethio-Arabian "Surre-Hanakiya" style, an attribution which is supported by other types of archaeological data. These new rock art sites are also compared with other rock art sites in Ethiopia. Archaeological faunal data from northern Ethiopia and elsewhere in Ethiopia is discussed and questions are raised about the validity of the hypothesized ages of the rock art in south-central Ethiopia. [ABSTRACT FROM AUTHOR]

Obsidian is abundant in the Main Ethiopian Rift (MER). Petrological and geochemical features of obsidian from four volcanic centers in the MER, namely Birenti, Dofen, Fentale and Kone, are presented. Compositional and petrological variability is noted among the Dofen and Fentale obsidian, but not in those from Kone and Birenti where each have separate but uniform elemental composition. The Fentale and Kone obsidian were source materials for the artifacts of a number of Middle Stone Age and Later Stone Age/Neolithic sites in the region. We have yet to determine whether Dofen and Birenti were sources for archeological artifacts. The study also shows that volcanic episodes from a single center do not necessarily result in compositional variability. [ABSTRACT FROM AUTHOR]

The Sof Omar Cave System, a spectacular and extensive cave system in Southeastern Ethiopia represents a maze of dry cave passages, which subsequently were crossed by a subterranean watercourse formed by the Weib River, forming combined underground passages of a total length of 15.1 km, the longest and most extensive in Ethiopia. The Sof Omar cave and subterranean river system developed on Jurassic limestone beds particularly on the Gebredarie Series (massive, crystalline limestone beds intercalated with thin marl and mudstone beds). The cave system and the subterranean River developed along a generally horizontal outline within a 20 m thick layer. The Sof Omar gorge is a wide but shallow doline, whose central section is incised by the ancient surface route of the Weib River. Prominent half dolines opening toward the sink and resurgence areas, as well as consistently inward dipping limestone beds at these localities imply collapse phenomenon. Karstification triggered by rift-related uplifting and extension during the mid-Miocene East African rifting, accompanied by extensive collapse along bedding planes likely initiated the caving process. The rifted and collapsed chambers were later widened by slow but persistent dissolution. The dry cave passages were formed earlier than the subterranean river course, though the latter might have partly followed the pre-existing cave passages and enlarged them to form the current subterranean river course. The Sof Omar caves are still at the heart of the cultural and religious life of the local population, where the dry cave passages, domes, and chambers are considered as important religious and cultural locales. With its subterranean river, large chambers connected by narrow and long rift passages, a unique and prominent sinkhole above the caves, wooded gorge teeming with numerous and unique tropical plant and bird species, the Sof Omar Cave System and adjoining gorge has outstanding scenic values. Apart from these naturally outstanding values, what makes the Sof Omar Cave System unique and unsurpassed in the world is its cultural significance. The caves form part of the cultural and religious life of the local population leading to the unique harmony between nature and culture. The cave system and its adjoining forested gorge is a natural–cultural heritage site that requires an active geoconservation. [ABSTRACT FROM AUTHOR]

Abstract: Lalibela is a medieval settlement in Northern Ethiopia famous for its 11 beautifully carved rock hewn churches, registered as World Heritage Site in 1978. The rock hewn churches are grouped into three based on their proximity: the Bete Medhane Alem (Church of the Holy Saviour), Bete Gabriel–Rufael (Church of St. Gabriel–Rafael) and Bete Giorgis (Church of St. George) groups. The churches are carved out of a single, massive scoriaceous basalt hill which was deposited along an East–West extending palaeovalley in the Oligo-Miocene Trap basalt of the northwestern Ethiopian plateau. The Rock Mass Rating (RMR) classification scheme was used to classify the rock mass (assuming each church as a separate rock mass) based on their uniaxial compressive strength and the spacing and conditions of discontinuities. Though most of the churches are hewn from medium to high strength rock mass, discontinuities make them vulnerable to other deteriorating agents mainly weathering, and water infiltration. Most of the rock hewn churches are affected by pre-carving cooling joints and bedding plane discontinuities, and by mostly but not necessarily post-carving tectonic and seismic induced cracks and fractures. Material loss due to deep weathering triggered by rain water infiltration and uncontrolled groundwater seepage affects most of the churches, particularly the Bete Merqorios (Church of St. Mark) and Bete Aba Libanos (Church of Father Libanos) churches. The scoriaceous basalt which is porous and permeable allows easy passage of water while the underlying basalt is impermeable, increasing the residence time of water in the porous material, causing deep weathering and subsequent loss of material in some of the churches and adjoining courtyards. [ABSTRACT FROM AUTHOR]

An annually laminated, uranium-series dated, Holocene stalagmite from southeast Ethiopia has been analysed for growth rate and δ13C and δ18O variations at annual to biennial resolution, in order to provide the first long duration proxy record of decadal-scale rainfall variability in this climatically sensitive region. Our study site (10°N) is climatically influenced by both summer (June-August) and spring (March-May) rainfall caused by the annual movement of the Inter- Tropical Convergence Zone (ITCZ) and modulated by large-scale anomalies in the atmospheric circulation and in ocean temperatures. Here we show that stalagmite growth, episodic throughout the last 7800 years, demonstrates decadal-scale (8-25 yr) variability in both growth rate and δ18O. A hydrological model was employed and indicates that this decadal variability is due to variations in the relative amounts of rainfall in the two rain seasons. Our record, unique in its combination of length (a total of ∼1000 years), annual chronology and high resolution δ18O, shows for the first time that such decadal-scale variability in rainfall in this region has occurred through the Holocene, which implies persistent decadal-scale variability for the large-scale atmospheric and oceanic driving factors. [ABSTRACT FROM AUTHOR]

The Negash pluton (50 km2) consists of late Pan-African, high-K, calc-alkaline granitoids intruded into low-grade metavolcanics–metasediments. This almost circular massif consists of monzogranites, granodiorites, diorites–gabbrodiorites, and hybrid diorites. The anisotropy of magnetic susceptibility (AMS) method was used to determine internal structures of the pluton. The foliation trajectories are concentric and inward dipping. The lineation pattern displays an external zone characterised by horizontal concentrically oriented lineations and an internal zone with NW–SE oriented lineations. These petro-structural data clearly locate the feeder zone at the north-western tip of the pluton and indicate the subsequent expansion of the magmas towards the SE. The pluton is a result of in-situ assembly of four magma batches, which were forcefully injected into pre-existing foliated country rocks in relation to transpressional tectonic regime. Two types of mafic–felsic magma interactions are recognised: homogeneous and heterogeneous hybrid diorites at the north-western part, and mingled interfaces at the diorite–granodiorite contact zones mainly visible in the eastern and south-eastern parts. The in-situ mingling along diorite–granodiorite contacts was achieved at the level of emplacement during the injection of dioritic magma into the felsic magmas while the hybrid diorites are assumed to result from two-way conduit mixing and mingling during simultaneous rising of mafic and felsic magmas. [Copyright &y& Elsevier]

Detailed geological and geochemical characterization is crucial to support soil studies in such geologically and topographically complex systems as the Gilgel Gibe catchment in southwestern Ethiopia. Field studies, as well as mineralogical, petrological and geochemical analyses on selected rock samples and their weathering products revealed that the catchment is dominantly underlain by rhyolites and trachytes, which occur as both lava flows and pyroclastic associations. Most of the lavas have a trachytic texture, while few others are massive or show spherulitic or perlitic texture. The rocks have a SiO 2 -content ranging from about 62 to 73 wt% (intermediate to felsic composition, on an anhydrous base) and a relatively high Na 2 O + K 2 O content ranging from about 9 to 12 wt% (anhydrous base). The dominant phenocrysts present in the rocks are plagioclase, sanidine and Fe–Ti oxide minerals. Alkali-rich amphiboles and quartz occur in most of them, while hornblende, titanite and clinopyroxene are rare. The amount of phenocrysts varies from less than 1 vol.% to about 30 vol.%. The pyroclastic associations are discontinuously scattered within the study area. They all have a glassy matrix (vitrophyric texture) and are composed of a mixture of lithics, crystals and glass. In comparison with the lava samples, the pyroclastic samples exhibit a more variable chemistry. In contrast, the X-ray diffractograms of the pyroclastic deposits and the lavas show little difference. The Chemical Index of Alteration values for the studied samples vary from 53 to 99 indicating moderate to high intensity of weathering. Samples from lava flows have shown less degree of weathering than samples of the pyroclastic associations. [ABSTRACT FROM AUTHOR]

Abstract: Landslide hazard is one of the crucial environmental constraints for the development of Ethiopia, representing a limiting factor for urbanization and infrastructures. The high relief and the rugged topography induced by a strong Plio-Quaternary uplift, the occurrence of clayey horizons within the sedimentary sequences, the dense network of tectonic fractures and faults, the thick eluvial mantles on volcanic outcrops, and the thick colluvial–alluvial deposits at the foot of steep slopes are the predisposing factors for a large variety of mass movements. Heavy summer rainfall is the main triggering factor of most landslides, some of which undergo a step-like evolution with long-lasting quiescence intervals. First generation movements are commonly restricted to shallow phenomena, such as soil slips or mud flows in eluvial–colluvial material. Fast moving slope failures, such as rock slides, topplings and falls, are also triggered by earthquakes. To mitigate the landslide risk, any first priority measure should include adequate drainage of slopes in order to reduce water infiltration. On the other hand, appropriate site selection for buildings, transferring risky settlements, accurate geological control of works, and education campaigns are all strongly recommended. [Copyright &y& Elsevier]

During the past 25 ka, southern Ethiopia has undergone tremendous climatic changes, from dry and relatively cold during the Last Glacial Maximum (LGM, 25–18 ka) to the African Humid Period (AHP, 15–5 ka), and back to present-day dry conditions. As a contribution to better understand the effects of climate change on vegetation and lakes, we here present a new Predictive Vegetation Model that is linked with a Lake Balance Model and available vegetation-proxy records from southern Ethiopia including a new phytolith record from the Chew Bahir basin. We constructed a detailed paleo-landcover map of southern Ethiopia during the LGM, AHP (with and without influence of the Congo Air Boundary) and the modern-day potential natural landcover. Compared to today, we observe a 15–20% reduction in moisture availability during the LGM with widespread open landscapes and only few remaining forest refugia. We identify 25–40% increased moisture availability during the AHP with prevailing forests in the mid-altitudes and indications that modern anthropogenic landcover change has affected the water balance. In comparison with existing archaeological records, we find that human occupations tend to correspond with open landscapes during the late Pleistocene and Holocene in southern Ethiopia. [ABSTRACT FROM AUTHOR]

Despite eastern Africa being a key location in the emergence of Homo sapiens and their subsequent dispersal out of Africa, there is a paucity of long, well-dated climate records in the region to contextualize this history. To address this issue, we dated a ∼293 m long composite sediment core from Chew Bahir, south Ethiopia, using three independent chronometers (radiocarbon, 40Ar/39Ar, and optically stimulated luminescence) combined with geochemical correlation to a known-age tephra. The site is located in a climatically sensitive region, and is close to Omo Kibish, the earliest documented Homo sapiens fossil site in eastern Africa, and to the proposed dispersal routes for H. sapiens out of Africa. The 30 ages generated by the various techniques are internally consistent, stratigraphically coherent, and span the full range of the core depth. A Bayesian age-depth model developed using these ages results in a chronology that forms one of the longest independently dated, high-resolution lacustrine sediment records from eastern Africa. The chronology illustrates that any record of environmental change preserved in the composite sediment core from Chew Bahir would span the entire timescale of modern human evolution and dispersal, encompassing the time period of the transition from Acheulean to Middle Stone Age (MSA), and subsequently to Later Stone Age (LSA) technology, making the core well-placed to address questions regarding environmental change and hominin evolutionary adaptation. The benefits to such studies of direct dating and the use of multiple independent chronometers are discussed. • Four independent dating methods applied to ∼293 m lake core from southern Ethiopia. • Reveals 620 ka high-resolution sedimentary record near key fossil hominin sites. • Mean accumulation rate of 0.47 mm/a comparable to other African lacustrine sediments. • Accumulation rate fell to 0.1 mm/a during MIS 2, likely due to reduced sediment supply. • Use of multiple independent chronometers is a powerful approach in lake settings. [ABSTRACT FROM AUTHOR]