Geology and Geomorphology

Abstract

Ethiopia is characterized by a wide variety of geological formations and geomorphological features. The major rock types on the basis of chemical and mineralogical composition of Ethiopia include the Precambrian metamorphic rocks with associated plutonic igneous rocks which form the basement, the Paleozoic-to-Mesozoic sedimentary rocks, Cenozoic basic and felsic volcanic rocks with intercalated sedimentary rocks. Internal earth processes including metamorphism, folding, faulting, Paleozoic–Mesozoic sedimentation, and Cenozoic volcanism set the ground for surface processes. Erosion and deposition modified the physiography and landforms, which, in turn, influenced soil formation and distribution in Ethiopia. The major geomorphologic elements are summits and crests straddling the nearly flat surfaces of the plateau volcanic pile; plateaus (the western and eastern highlands without the overlying volcanic massifs); flat-gently sloping Rift Valley (main Ethiopia Rift and the Afar depression); the Ogaden Plains; and low-lying areas in the west, southwest, and southern peripheral parts of the country; bottom areas which include the lake basins and areas lying below 500 m a.s.l. The major soil types vary in response to parent materials and landforms among other factors of soil formation. Rock types affect soil texture and mineralogy while landform affects spatial distribution of soils due to complex erosion and depositional processes. Nitisols and Vertisols dominate on basalt formation whereas leptosols exclusively dominate hill slope irrespective of the geological formation. Understanding parent materials and land form is crucial toward understanding, mapping, and managing soil resources.