Analysis of the influence of tectonics on the evolution of valley networks based on Srtm Dem, Jemma River basin, Ethiopia

The Ethiopian Highlands are a good example of a high plateau landscape formed by a combination of tectonic uplift and episodic volcanism. Deeply incised gorges indicate active fluvial erosion, which leads to instabilities of over-steepened slopes. In this study we focus on the Jemma River basin, which is a left bank tributary of the Abay - Blue Nile in order to assess the influence of neotectonics on the evolution of its river and valley network. Tectonic lineaments, shape of valley networks, direction of river courses and intensity of fluvial erosion were compared in six subregions, which were delineate beforehand by means of morphometric analysis. The influence of tectonics on the valley network is low in the older deep and wide canyons and on the high plateau covered with Tertiary lava flows, whilst in the younger upper part of the canyons it is high. Furthermore, the coincidence of the valley network with the tectonic lineaments differs in the subregions. The direction of the fluvial erosion along the main tectonic zones (NE-SW) made it possible for backward erosion to reach far distant areas in the east. This tectonic zone also separates older areas in the west from the youngest landscape evolution subregions in the east, next to the Rift Valley.