Where it is and what it carries
The Somali Plate covers the eastern side of Africa and a large part of the western Indian Ocean. On land it holds nearly all of Kenya, Tanzania, Somalia, Uganda, Rwanda and Burundi, plus the whole of Madagascar. About half of Ethiopia and roughly 79% of Mozambique also sit on it. Island nations such as Seychelles, Mauritius and Comoros ride on its oceanic part, as do the French islands of Réunion and Mayotte.
PB2002 classes it as a minor plate. Many textbooks still draw a single African Plate, and treat the Somali block as part of it.
The East African Rift
The plate’s western edge is the East African Rift, the boundary with the African Plate. It runs about 9,000 km, mostly as continental rift with stretches of strike-slip faulting. The eastern branch cuts through Ethiopia, Kenya and Tanzania, and the western branch follows a chain of deep lakes including Albert, Tanganyika and Malawi. Relative motion across the rift averages only 0.3 cm/yr in PB2002, reaching about 0.6 cm/yr in places.
This slow pace is why the plate’s status is debated. GPS shows the two sides moving apart, but the southern end of the boundary, through Mozambique and the Mozambique Channel, is diffuse. Some researchers divide the region into extra blocks, including the Victoria microplate between the two rift branches and the Rovuma microplate farther south.
Ocean ridges on its other edges
Every boundary of the Somali Plate is mainly divergent in PB2002. In the north, the Gulf of Aden spreading ridge separates it from the Arabian Plate at about 2.4 cm/yr. The Carlsberg Ridge and the northern Central Indian Ridge divide it from the Indian Plate at about 3.0 cm/yr. Farther south, the Central Indian Ridge meets the Australian Plate, the plate’s fastest boundary at about 4.0 cm/yr and up to 5.0 cm/yr.
The Southwest Indian Ridge forms the southern edge with the Antarctic Plate, opening at only about 1.2 cm/yr. The Rodrigues Triple Junction, where three Indian Ocean ridges meet, marks the plate’s southeastern corner.
Earthquakes and volcanoes
The plate has had 23 earthquakes of magnitude 6.5 or larger since 1900, none of them magnitude 8. The largest, a M7.2 in 1990, struck about 69 km east-northeast of Juba, South Sudan, in the same sequence as a M7.1 on the African side of the boundary. A M7.0 hit central Mozambique in 2006, and a M6.8 shook the Lake Tanganyika area near Kalemie in 2005. At sea, the Carlsberg Ridge produced a M7.0 in 1904 and the Prince Edward Islands region a M6.8 in 2023.
The dataset lists 49 volcanoes. Ol Doinyo Lengai in Tanzania is the only active volcano known to erupt natrocarbonatite lava, which flows black and weathers white. Piton de la Fournaise on Réunion is one of the most active volcanoes in the world, and Karthala on Grande Comore has a large summit caldera. Off Mayotte, a new submarine volcano, Fani Maore, grew on the seafloor from 2018. Ardoukoba in Djibouti, Meru in Tanzania and several volcanoes in Kenya’s section of the rift, including The Barrier and Emuruangogolak, complete the list of well-known centers.