Plate data: Bird (2003), PB2002, converted by Hugo Ahlenius, Nordpil (ODC-By 1.0). Land: Natural Earth (India POV).
The Somali Plate carries the eastern side of Africa, from most of the Horn of Africa down the east coast, plus Madagascar and much of the western Indian Ocean floor. PB2002 calls it the Somalia plate. It is the largest of the 38 small plates1 that Bird (2003) added to the 14 large plates of the NUVEL-1A model.
Its western edge is the East African Rift. USGS describes the rift as a place where a new spreading center may be developing under Africa, and says East Africa may be the site of the Earth's next major ocean. If spreading continues, the Indian Ocean could flood the area and make the Horn of Africa a large island.
Bird writes that McKenzie and others, in 1970, were probably the first to use the name Somalian plate. Later studies found that adding a separate Somali plate improves the fit to the data, and Chu and Gordon (1999), using more spreading data from the Southwest Indian Ridge, found that the Somali and African Plates move distinctly with high confidence. The motion Bird adopts gives about 6 mm per year of separation at the north end of their boundary and slight compression, 1 to 2 mm per year, at the southern end.
The rift has two branches. Bird drew the PB2002 boundary along the western branch, through the Malawi and Tanganyika rifts, because it has more earthquakes. On this map that puts Lake Tanganyika on the African Plate and Lake Malawi on the Somali Plate.2
Somali Plate in numbers
Measured from its PB2002 outline, the Somali Plate covers about 19.2 million km², or 3.8% of the
Earth's surface. That makes it number 8 by area of the 52 plates in the model.
It spans from 47°S to 15°N and from 27°E to 70°E.
Its edge is about 23,464 km long, mostly divergent:
58.7%divergentDivergent boundary. Plates pull away from each other and new crust forms between them. Source (13,763 km)
, 9.2%convergentConvergent boundary. Plates move toward each other and crust is destroyed as one plate dives under another. Source (2,150 km)
and 32.2%transformTransform boundary. Plates slide horizontally past each other. Crust is neither made nor destroyed. Source (7,551 km)
.
Countries whose main landmass sits on this plate: Burundi, Djibouti, Ethiopia, Kenya, Lesotho, Madagascar, Malawi, Mozambique, Rwanda, S. Sudan, Somalia, South Africa, Tanzania, Uganda and eSwatini. Countries that straddle a boundary
are listed under the plate that holds the center of their largest landmass.
Along its boundaries it moves a mean 1.6 cm/yr relative to its neighbors, fastest against the Australian Plate. Bird (2003)
Neighboring plates Neighbors. Plates that share a boundary with this plate. Most plate movement happens along these narrow zones between plates. Source
The Somali Plate shares a boundary with 5 plates in PB2002, longest shared edge first.
The longest, about 9,042 km, is with the African Plate; the shortest, about 1,923 km, is with the Arabian Plate.
