A large rift valley cuts through the eastern portion of Africa. This rift, and associated seismicity and volcanism, is a result of plate tectonic activity. The Afar Triangle is a low area near a region where Arabia, East Africa, and West Africa are splitting apart where the Red Sea and Gulf of Aden meet.
The following images show topography and its relation to this plate tectonic boundary.
Image from the National Geophysical Data Center
Image from the USGS