| Description |
viii, 106 leaves : illustrations, maps ; 28 cm |
| Summary |
This study examines the morpho-tectonic evolution of the drainage system in the northwestern Ethiopian plateau by focusing on the Tekeze and the Blue Nile Rivers. The plateau is underlain by Precambrian crystalline rocks, overlain by Mesozoic sedimentary section that is topped with a 1-3 km thick pile of Oligocene-Quaternary volcanic rocks. It is bounded in the east and southeast by the Afar Depression (AD) and the Main Ethiopian Rift (MER). Satellite derived Digital Elevation Models are analyzed using ArcGIS and RiverTools to extract morpho-tectonic parameters of tributaries of the Tekeze and Blue Nile Rivers including Normalized Steepness Index (K[subscript sn]), Concavity (theta), Regression Fit (r²), and spatial distribution of major and minor knickpoints and faults. Two end-member models have been previously proposed: 1) a steady-state rate of incision since the beginning of the development of these drainage systems (~30 Ma) or 2) a rate of incision that increased through time. This study shows that the incision history of these drainage systems is more complex than can be explained by these two end-member models. Nevertheless, the models are still valid explanations for specific regions of the plateau. The evolution of the drainage systems on the NW plateau is influenced by three tectonic and geological events: 1) The rising of the Afar mantle plume (~30 Ma) created a moderate increase in the incision rate of the entire plateau, 2) a localized increase in the incision rate associated with the shield volcanoes build-up event (~22 Ma) and lastly 3) a significant increase of the incision rate in the eastern part of the northwestern plateau due to rift-flank uplift on western escarpment of the AD and the northwestern escarpment of the MER. This uplift diminishes westward leaving the drainage system in the lower reaches of the Tekeze and Blue Nile Rivers relatively tectonically undisturbed, hence establishing a long-lived hydrological stability and reaching steady-state equilibrium--Abstract, leaf iii. |
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