DECONVOLVING THE CONTROLS OF LANDSCAPE EVOLUTION OF THE ETHIOPIAN PLATEAU IN A CONTINENTAL RIFT SETTING

Over the past decade, the study of investigating tectonic-incision-climate coupling for landscape evolution has received considerable momentum. Many orogenic regions around the world like parts of the Tibetan Plateau, Andes, and Himalayas are argued to be in transient conditions, thus adjusting to tectonic, climate and/or geomorphic variables. The anomalous topography of the Ethiopian Plateau in East Africa is uniquely situated to study transient landscape since its location to a non-orogenic rift setting. The plateau has undergone extensive and deep incision by the Blue Nile and Tekeze Rivers in the proximity of the uplifted flanks of the Main Ethiopian Rift, Afar Depression and the Red Sea Rift systems.

Here, we investigate DEMs-derived erosional map and tributary-long profile forms (steepness indices and knickpoint patterns) of the Blue Nile and Tekeze Rivers and compare these results with existing P-wave velocities of upper mantle within the Ethiopian Plateau to understand landscape evolution of the plateau. Our erosion map reveals that majority of incisions occur along main tributaries where normalized steepness indices are higher in channels with higher magnitude of incision across the plateau interior and along the rift-flanks. The positions and patterns of more than 170 major knickpoints and associated normalized steepness indices of the channels indicate that these knickpoints are transient features of the plateau adjusting to differential uplift. Statistical correlation of normalized steepness indices and incision magnitudes with mantle velocities shows that the regions with high normalized steepness indices and high incisions are underlain by anomalously low velocity zones thus hot mantle. This suggests that the present day topography of the plateau is largely controlled by dynamic uplift of the area. The positions of major knickpoints above these low velocity zones also indicate that mostly the dynamic uplift in the plateau interior and flexural uplift in back-tilted rift margins control incision of the Ethiopian Plateau.