Scientists haven’t yet reached a consensus on the exact mechanics of continental break-ups, but the fact that it’s happening here isn’t new or unexpected.
Tectonic plates typically “glide” very, very slowly over the asthenosphere, the upper layer of the Earth’s mantle, most likely due to convection currents and forces acting at plate boundaries
A large crack, stretching several kilometres, made a sudden appearance recently in south-western Kenya. The tear, which continues to grow, caused part of the Nairobi-Narok highway to collapse. Initially, the appearance of the crack was linked to tectonic activity along the East African Rift.
The rifting, which began about 25 million years ago, will eventually create two separate continental masses associated with the Somalian and Nubian tectonic plates. The process, however, will take millions of years at the current spreading rate of a few millimeters per year.
Splitting a continent in two is quite common, for instance, it led to the opening of the Atlantic Ocean. Notice how Africa and South America would fit perfectly together, this is because they were once one landmass, eventually sutured apart by the Mid-Atlantic Ridge.
WHY AFRICA WILL SPLIT
When the lithosphere is subject to a horizontal extensional force it will stretch, becoming thinner. Eventually, it will rupture, leading to the formation of a rift valley.
Continental rifting requires the existence of extensional forces great enough to break the lithosphere. The East African Rift is described as an active type of rift, in which the source of these stresses lies in the circulation of the underlying mantle. Beneath this rift, the rise of a large mantle plume is doming the lithosphere upwards, causing it to weaken as a result of the increase in temperature, undergo stretching and breaking by faulting.
Evidence for the existence of this hotter-than-normal mantle plume has been found in geophysical data and is often referred to as the “African Superswell”.
When this happens, a new ocean will begin forming by the solidification of magma in the space created by the broken-up plates. Over a period of tens of millions of years, seafloor spreading will progress along the entire length of the rift.