Planation Surfaces
The Dogu’a Tembien woreda covers part of the north-western highlands of Ethiopia (Fig. 10.1 ). Its spectacular landscape comprises not only steep escarpments and deeply incised river canyons, but also a number of conspicuous low-relief plains and flat-top
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The Dogu’a Tembien woreda covers part of the north-western highlands of Ethiopia (Fig. 10.1). Its spectacular landscape comprises not only steep escarpments and deeply incised river canyons, but also a number of conspicuous low-relief plains and flat-topped hills known locally as ambas, which give the landscape a stepped appearance. These landforms and landscapes result from a geological history that has extended from the latter part of the Precambrian, some 800 million years ago, to the present. Their evolution is related to the structural history of the region, to volcanic and subvolcanic activities, to the environments and conditions that existed during the deposition of the sediments and, since that time, to the composition of the resulting rocks and to their resistance to weathering and erosion, especially during the uplift that is still continuing. Surfaces with a flat or almost flat relief that have resulted from erosion and often cut across different geological structures and rock types are called planation surfaces. Models of landscape evolution generally assume that such surfaces develop at low elevations, close to sea level, so their existence at a variety of elevations in the highlands of northern Ethiopia might at first seem surprising. Four planation surfaces, each occurring at a different elevation, have been recognized in northern Ethiopia. These surfaces represent unconformities (past breaks in sedimentation, R. Bussert (&) Institut für Angewandte Geowissenschaften, Technische Universität Berlin, Berlin, Germany e-mail: [email protected] M. Coltorti University of Siena, Siena, Italy F. Dramis Roma Tre University, Rome, Italy © Springer Nature Switzerland AG 2019 J. Nyssen et al. (eds.), Geo-trekking in Ethiopia’s Tropical Mountains, GeoGuide, https://doi.org/10.1007/978-3-030-04955-3_10
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Fig. 10.1 Map of central part of northern Ethiopia, based on a shuttle radar topography mission (SRTM) digital elevation model (CGIAR-CSI SRTM 90 m DEM). Major escarpments and river canyons have been marked. Square box outlines the region discussed in the text
often accompanied by widespread erosion) that have been buried and subsequently exposed (or exhumed) due to uplift and renewed erosion. They have been named (from the oldest to the most recent) as PS1 (a pre-Ordovician planation surface), PS2 (a late Triassic planation surface), PS3 (an early Cretaceous planation surface), and PS4 (a planation surface beneath the Ethiopian ‘Trap’ flood basalts) (Fig. 10.2). Good examples of exhumed planation surfaces are the low-relief Precambrian basement landscapes (PS1) to the west and north of the Dogu’a Tembien district and the flat-topped sandstone feature known as Mount Amba
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Planation Surfaces
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Fig. 10.2 Stratigraphy of the Dogu’a Tembien district and surrounding area, showing major unconformities and main geological events
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Aradam (PS4) to the south of Mekelle. Other low-relief surfaces are also recognizable in the Dogu’a Tembien landscape and
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