The Afar region in Northern Ethiopia is the centre of a “Y” shaped rift system, where the continental lithosphere is being stretched and is splitting.

The Arabian Plate is rifting away from the African plate along an active divergent ridge system, to form the Red Sea and Gulf of Aden. The rifting then extends southwards where the African Plate is itself becoming stretched along the line of the East African Rift Valley and is splitting to form two new plates; the Nubian and Somalian Plates.

The point in the Afar region where the boundaries of all three plates meet is called a Triple Junction.

In time, as Nubian and Somalian plates move further away from each other, the area between them will grow thinner and drop below sea level. New ocean lithosphere may form along the centre of the rift, producing a new narrow ocean basin with its own mid ocean ridge.

The orientation of the rifts, highlands and associated volcanic activity (such as the volcano Erta Ale) suggests that the rifting of the continental lithosphere is the result of a “hot spot”, possibly formed by a rising mantle plume, beneath the Afar region where an upwelling mantle plume is forcing up the region. This causes the brittle lithosphere to stretch and fracture and is accompanied by large outpourings of lava called “flood basalts” which are typical of the Afar region.

 

Afar region triple junction.
Afar: darker shading. Volcanoes: red triangles.

Image: From ‘This Dynamic Earth’ by Kious and Tilling, courtesy of the US Geological Survey