Is Africa gonna split in two?

Is Africa gonna split in two?

Don’t worry, it is not going to happen anytime soon, but geologists observe the formation of oceanic crust in Ethiopia. How is it possible since Ethiopia is obviously land and not ocean? What is happening exactly? What does it mean for the country and the future? An explanation is needed, from basic plate tectonics to oceanic crust creation, so here we go.

Tectonic plates

The Earth is constituted of several layers: the core, the mantle, the crust. The lithosphere regroups the crust and the upper part of the mantle. It is divided in large chunks called tectonic plates.

Tectonic plates map
Map of all tectonic plates and their movements (source: USGS).

Those plates move around, going apart, going affront or moving next to each other. This causes various geological events such as earthquakes, volcanic formations, mountain formation [1].

It is this phenomenon that is responsible for continental drift and shapes the world in the way it is nowadays.

On the top of the plates is crust. This crust’s composition depends on its location. We distinguish continental crust and oceanic crust.

Collision, subduction and mid-ocean ridge

Since plates are moving, several events can happen depending on the behaviour.

If two continental crusts are converging, we have a collision. Because they both have the same composition the crust of both plates will be pushed upwards. This leads in mountain formation.

If an oceanic crust converge to either a continental crust or another oceanic crust, we have a subduction. In the case of oceanic versus continental, the oceanic crust being thinner will slide beneath the continental crust. In the oceanic versus oceanic case, one of them will have the same fate. Pockets of magma can be found underneath the oceanic crust, sometimes reach the surface and form volcanoes. (trivia: we say magma when it is beneath the surface and lava when it reaches the surface)

If two crusts diverge, they form what is called a mid-ocean ridge. It is from that ridge that oceanic crust is produced and expands as the plates moves.

Oceanic crust

The magma from the mantle finds its way to the surface where the ridge is. The magma encounters cold water and solidifies due to the difference of temperature. It forms the upper part of the oceanic crust.

Schematic of an oceanic ridge
Oceanic ridge with mantle reaching the surface and oceanic crust expansion (source: NASA).

This crust is composed of basalt and gabbro. It is laying over lithospheric mantle composed of peridotite.

Oceanic crust is between 10 and 80 kilometres thick depending on its age. In comparison, continental crust is between 150 and 200 kilometres thick.

What happens in Ethiopia

Ethiopia is located at a triple point, the intersection of the Arabian plate, the Nubian plate and the Somalian plate. The East African rift is in the Afar region, southwest of the Red Sea rift and west of the Gulf of Aden rift. [2]

Schematic of the Ethiopian rift
Triple junction of Arabian, Nubian and Somalian plates. [2]

However, even if a rift exists, it doesn’t necessarily mean it will turn into an oceanic ridge and form an ocean [3]. It is too complex so far to predict the future because our knowledge of plates movements, of their behaviour, is still incomplete.

The rift in Ethiopia
The rift in Afar, Ethiopia, that is separating Africa and Arabia and will eventually form a new ocean. (source: © University of Rochester)

Africa might tear apart the same way America was separated from Europe and Africa 80 Ma (million years ago), creating Atlantic Ocean. If it would, it won’t be until millions of years from now.

References

[1] All You Need Is Science, Science Fun Facts #2

[2] E. Lewi, D. Keir, Y. Birhanu, J. Blundy, G. Stuart, T. Wright and E. Calais; “Use of a high-precision gravity survey to understand the formation of oceanic crust and the role of melt at the southern Red Sea rift in Afar, Ethiopia”; Geological Society, London, Special Publications, 420, 165-180, 16 December 2015, https://doi.org/10.1144/SP420.13

[3] Klemetti, E. (2020), Are we seeing a new ocean starting to form in Africa?, Eos, 101,https://doi.org/10.1029/2020EO143740

 

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