Morpho-tectonic analysis of the Tekeze River and the Blue Nile drainage systems on the Northwestern Plateau, Ethiopia

This study examines the morpho-tectonic evolution of the drainage system in the Northwestern Plateau in Ethiopia dominated by the Tekeze River and the Blue Nile. The Northwestern Plateau is underlain by Precambrian crystalline rocks, followed by Mesozoic sedimentary section and topped with Oligocene–Quaternary volcanic rocks. The plateau is bounded in the east and southeast by the Afar Depression and the Main Ethiopian Rift, respectively. Digital Elevation Models (DEMs) from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM) data are analyzed to extract morpho-tectonic parameters including the Normalized Steepness Index (Ksn), the Concavity (θ) and the Regression Fit (r2) between the observed and predicted channel profiles from the sub-basins and the tributaries of the Tekeze River and the Blue Nile. Analysis of these morpho-tectonic parameters has shown that the evolution of the drainage systems on the Northwestern Plateau was influenced by three tectonic and geological events. The first event resulted in a broad and regional uplift of the plateau, most likely due to the rise of the Afar mantle plume ∼30 Ma. This regional uplift was accompanied by moderate incision rate of the Tekeze River and the Blue Nile drainage systems within the entire Northwestern Plateau. The second event, which was in the form of shield volcanoes build-up, occurred at ∼22 Ma and resulted in localized increase in the incision rate around these volcanoes. The third event is manifested by rift-flank uplift at ∼11 Ma on the western escarpments of the Afar Depression and the northwestern escarpments of the Main Ethiopian Rift. This event resulted in an increase in the incision rate of the Tekeze River and the Blue Nile drainage systems, but this increase seems to diminish towards the west and northwest leaving the drainage systems in the lower reaches of the two rivers relatively tectonically undisturbed, hence allowing for the establishment of a long-lived hydrological stability.

► This study examined drainage incision and tectonic uplift of the Northwestern Plateau, Ethiopia.
► It focused on the Tekeze River and the Blue Nile drainage systems.
► Incision was moderate at 30 Ma driven by regional uplift related to the rise of the Afar mantle plume.
► Local increase of incision at 22 Ma was related to volcanoes built-up event within the plateau.
► At 11 Ma local increase of incision was related to flank uplift of rift systems to the east.