The Ethiopian rift valley: geography and morphology

The Ethiopian sector of the East African Rift system extends for more than 1000 km in a NE-SW to N-S direction from the Afar depression, at Red Sea-Gulf of Aden junction, southwards to the Turkana depression. The southern boundary may be traced at latitude ~5°N, south of the area where the rift is divided into two branches (Chamo basin to the west and Galana basin to the east) by the Amaro Mts; southwards, the rift zone widens and deformation becomes more complex being accommodated by the ~300 km-wide system of basins and ranges (referred to as Broadly Rifted Zone) that characterizes the overlapping area between the Ethiopian and Kenya Rifts. To the north, the rift corresponds to the Afar depression, a wide triangular zone of tectonic collapse in which the rift valley joins the Red Sea and Gulf of Aden oceanic basins.

 

Morphology of the Ethiopian sector of the rift valley (click for a larger version)

 

The typical rift morphology is most typically developed in the Main Ethiopian Rift, a 500km-long sector that from the Afar depression (latitude 9°40'N) reaches the region of lakes Abaya and Chamo (latitude 5°30'N). In this rift sector, a ~80km-wide rift valley (Ethiopian Rift valley sensu stricto of Mohr, 1983) separates the uplifted western (Ethiopian) and eastern (Somalian) plateaus. Large tectonic scarps connect the valley floor with the surroundings plateaus; the plateaus rise to elevations >2000 m above sea level; north of latitude 9° the highest elevations are attained by the Ethiopian Plateau, whereas south of this latitude the Somalian plateau reaches the highest elevations. The rift floor raises in elevation from the Turkana depression up to the main watershed between the Meki and Awash rivers immediately north of Lake Ziway, where the rift valley attains its maximum elevation at ~1700 m asl. Northwards the rift floor descends regularly into the Afar depression where, over extensive areas, it lies below sea level. Local increases in the elevation of the rift valley are generally due to volcanic edifices, as in the northern MER where several volcanoes raise from the flat rift floor.

 

 

Topographic profiles and 3D digital elevation model of the Ethiopian sector of the rift valley (click for a larger version)