Plate Tectonics

East African Rift/ Rift Valleys

A Rift Valley is a lowland region that forms where earth's tectonic plates move apart. Rift Valleys are found both on land and the bottom of the ocean. Rift Valleys are different from other rifts , such as river valleys and glacial valleys because they are formed by tectonic activity and not by erosion . Tectonic plates are always in motion ,plates shifting against each other is called transform plate boundaries and falling beneath one another is called subduction, crashing against one another at convergent plate boundaries, and tearing apart from one another at divergent plate boundaries. Many of the Rift valleys are a part of a "triple junction". This is a type of divergent boundary where three tectonic plates meet at about a 120 degree angle.

Two arms of the triple junction can split to form an ocean while the third arm may become a rift valley. All of the rift valleys in the system are connected , but not a part of a single unit. Today Africa and Asia are connected by the triangle of the Sinai Peninsula. In time the Red Sea rift will separate Africa and Asia all together and connect the Mediterranean and Red seas. The Arabian plate , the Nubian plate and Somali plate are all tearing apart. Two arms of the afar triple junction continue to widen in the process of seafloor spreading. As these rifts continue, the narrow valley created by Gregory rift the arm of the afar triple junction located above sea level may sink low enough that the Arabian sea will flood it and Horn of Africa sitting on Somali plate would become a continental island such as Madagascar or New Zealand.

Throughout the East African rift ,the continent of Africa is splitting into two. The African plate also known as the Nubian plate carries most of the continent, while the smaller Somali plate carries the Horn of Africa. East African rift is a place where earth's tectonic forces are trying to create new plates by splitting apart. These two plates are moving away from one another and also away from the Arabian plate to the north. All the rifting in East Africa is not confined to the Horn of Africa. There is a lot more rifting activity further south, extending into Kenya, Tanzania and Great lakes region of Africa. Further to the south is the lake Albert rift which contains the East African great lakes. The complete Rift system extends 1000's of kilometers in Africa and 1000 more if we include the Red Sea.

How did these Rifts form ? One popular model for the East African Rift assumes that elevated heat flow from the mantle causes a pair of thermal bulges in central Kenya and the Afar region. These bulges can easily be seen as elevated highlands. As the bulges form , they stretch and fracture the outer crust. The stretching process is preceded by huge volcanic eruptions which flow over large areas and are usually exposed on the Rifts. The lava erupted on fractures runs over the land like water during a flood.

The rifting process described before occurs in a continental setting and is referred to as a continental rift. The rifting of East Africa is complicated by the fact that two branches have developed, one to the west which hosts the African great lakes , where the rift is filled with water, and another parallel rift to the east where it bisects Kenya north to south before entering Tanzania where it starts dying out. The East African rift system provides a modern look to help us understand how continents break apart.

work cited

“East Africa's Great Rift Valley: A Complex Rift System.” Geology, https://geology.com/articles/east-africa-rift.shtml.