Geology of the Tekeze River basin (Northern Ethiopia)

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

Subduction and continental collision in the Eastern Mediterranean during the closure of the Tethyan gateway

Plate tectonics and mantle dynamics controlled the continental collision and tectonics of the Eastern Mediterranean – Tethyan realm, including by closing the Tethys Seaway linking the Atlantic and Indo-Pacific oceans. This led to reorganizations in ocean circulation, diversification and migration of marine and terrestrial species, and climatic change. Here, I review some of the work on the geodynamics of the region, including on the evolution of topography, and how paleotopography was influenced by mantle convection and volcanism. Mantle convection appears to have had a significant impact on the paleoenvironment, including by ultimately establishing the Gomphotherium Landbridge in the Miocene, enabling greater faunal exchanges between Africa-Arabia and Eurasia

Long-term drainage system evolution in the Wabe Shebele River basin (SE Ethiopia - SW Somalia)

Large river systems play an important role in Earth dynamics since they exert an influence on geological, geomorphological, and geochemical processes. On the other hand, these landforms occur in a variety of topographic and plate tectonic settings and tend to persist for 107–108yr, resisting variations in environmental conditions. Both modern and ancient big rivers configurations suggest that the persistence of such features is much longer on passive margins with long-lasting continental tilting and long-term rainfall without interference from continental glaciation, desertification, and volcanism. The literature on the geological evolution of river systems concentrates almost entirely on large-scale river basins. Very little research has been done to understand the evolution of smaller river networks that have a much lower persistence because they are more sensitive to climatic and tectonic changes. In this work we focused on the Wabe Shebele River basin (SE Ethiopia, SW Somalia) that drains the eastern slope of the Horn of Africa. It is a medium-scale drainage system (drainage area of ~105km2) developed on a long-lived regional slope to the SE inherited from the Early Mesozoic and influenced by tectonic structures relative to a passive continental margin and slightly affected by volcanism. By taking into consideration the present topography (swath profiles, filtered topography, slope, local relief), the river network (river longitudinal profiles, channel gradient), and the ancient landforms present in the region, we demonstrate that the Wabe Shebele River basin, despite its medium scale, is a long-lived landform persisting at least since the Oligocene. The results show that even smaller river systems can have a long-term history in favorable tectonic and topographic conditions

Drainage system organization after mantle plume impingement: The case of the Horn of Africa

Continental areas affected by mantle plume dynamics are characterised by extensive high-elevated regions drained by large radial river networks. Despite successive isostatic adjustments and rifting events, several studies demonstrated that the persistence of these drainage systems for tens of millions of years is possible. In these geodynamic contexts rivers are precious sources of knowledge because, propagating the signals of tectonic and climatic changes across landscape, they shape the topography and allow to recognise the first-order imprint imposed by mantle plume. The Horn of Africa, characterised by the coexistence of a continental rift system, a large igneous province (continental flood basalts), and a wide uplifted plateau, is an ideal test site to investigate the interrelations between surface and deep processes. Studies demonstrated the long-term persistence of some river networks draining the region and the strong influence of dome-like uplift on their evolution. However a regional-scale quantitative river network analysis is missing, as well as, a complete evolutionary scenario of the Horn of Africa drainage system. In this study we quantitatively investigated the topographic configuration of the Horn of Africa and analysed the four principal drainage systems (Blue Nile, Tekeze, Omo, Wabe Shebele basins), extracting the river longitudinal profiles and the main topographic and hydrologic parameters. In order to reconstruct the evolution of the region, we elaborated the pre /syn- and post-flood basalts topographies and calculated the elevation gain and loss with respect to the present configuration. Finally, we delineated a possible future drainage system evolution by analysing the present drainage divides stability. The results allowed to reconstruct the evolutionary scenario of the Horn of Africa river network since Oligocene and to investigate the mutual influence between surface and deep processes in shaping the landscape, providing new constraints to understand the formation and evolution of a drainage system in a context of a topography supported by a mantle plume

Evolution of a hillslope by rock avalanches: insights from analog models

Rock avalanches are among the most hazardous processes on hillslopes because of high velocity, great dimensions, and long run-out distance. For this reason, understanding the dynamics and factors of rock avalanches and their role in hillslope evolution is crucial. Studies evidenced that occurrence and evolution of these phenomena are influenced by lithological, structural, and climatic factors. Statistical analysis on natural cases demonstrated correlations between slope geometry and rock avalanche volume. Most of the studies referred to experimental tests which represent powerful tools to understand these landslides. Many models focused on the mechanism leading to high velocity and long run-out, but few studies discuss the role of rock avalanches in the evolution of a bedrock hillslope. The influence of slope geometry and physical properties of the substratum on the dynamics of rock avalanches is poorly constrained. We present results from analog models of a hillslope evolving by base level lowering. We tested several slope widths and two analog materials. The experimental apparatus allowed for checking the mass of mobilized material at each step and for taking a 3D scan of the whole surface. Our results, coupled with a statistical analysis, indicated that hillslope evolution is influenced by the material internal friction and by the friction with box walls (i.e., valley walls) when the slope is narrow. Widening the slope, the influence of lateral friction disappears, confirming observations in other models and nature. These results represent a new contribution to understand the dynamics of rock avalanches on bedrock hillslopes

Evolution of continental-scale drainage in response to mantle dynamics and surface processes: An example from the Ethiopian Highlands

Ethiopia offers an excellent opportunity to study the effects and linkage between mantle dynamics and surface processes on landscape evolution. The Ethiopian Highlands (NWEthiopia), characterized by a huge basaltic plateau, is part of the African Superswell, awide region of dynamically-supported anomalously high topography related to the rising of the Afar plume. The initiation and steadiness of dynamic support beneath Ethiopia has been explored in several studies. However the presence, role, and timing of dynamic support beneath Ethiopia and its relationship with continental flood basalts volcanismand surface processes are poorly defined. Here, we present a geomorphological analysis of the Ethiopian Highlands supplying new constraints on the evolution of river network. We investigated the general topographic features (filtered topography, swath profiles, local relief) and the river network (river longitudinal profiles) of the study area.Wealso apply a knickpoint celerity model in order to provide a chronological framework to the evolution of the river network. The results trace the long-term progressive capture of the Ethiopian Highlands drainage system and confirm the long-term dynamic support of the area, documenting its impact on the contrasting development of the Blue Nile and Tekeze basins

Long-term, deep-mantle support of the Ethiopia-Yemen Plateau

Ethiopia is a key site to investigate the interactions between mantle dynamics and surface processes because of the presence of the Main Ethiopian Rift (MER), Cenozoic continental flood basalt volcanism, and plateau uplift. The role of mantle plumes in causing Ethiopia's flood basalts and tectonics has been commonly accepted. However, the location and number of plumes and their impact on surface uplift are still uncertain. Here we present new constraints on the geological and topographic evolution of the Ethiopian Plateau (NW Ethiopia) prior to and after the emplacement of the large flood basalts (40-20 Ma). Using geological information and topographic reconstructions, we show that the large topographic dome that we see today is a long-term feature, already present prior to the emplacement of the flood basalts. We also infer that large-scale doming operated even after the emplacement of the flood basalts. Using a comparison with the present-day topographic setting, we show that an important component of the topography has been and is presently represented by a residual, nonisostatic, dynamic contribution. We conclude that the growth of the Ethiopian Plateau is a long-term, probably still active, dynamically supported process. Our arguments provide constraints on the processes leading to the formation of one of the largest igneous plateaus on Earth