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The science behind the scenes - Fast and furious: witnessing the birth of Africa's new ocean

The surface of the Earth is constantly changing. Continents have collided and drifted apart, and new oceans have formed (over millions of years) to give us the Earth we have today. But the Earth is still changing and some surprising things are happening right now.

In Ethiopia in north east Africa something exciting is happening. In 2005, in the middle of the Afar desert, a crack opened and grew by 8 metres over 10 days. The gap filled with 2.5 cubic kilometres of molten rock – enough to fill the new Wembley stadium a staggering 1000 times! Since then the crack has been growing wider and longer. Scientists believe that a new ocean is slowly forming and will eventually split the African continent in two. This has happened because of volcanic eruptions, and the earthquakes that have been triggered by these eruptions. 

The Afar desert is the only place in the world where we can see tectonic plates growing apart at the Earth’s surface. Read more at http://see.leeds.ac.uk/afar.

Tectonic plates

So how does this happen? Tectonic plates are the outermost layer of the Earth, known as the lithosphere, and they are hard and rigid. Where one tectonic plate joins another, there will be seismic activity (earthquakes and volcanoes) along their edges. 

In the Afar desert three tectonic plates meet and are splitting apart – the Nubia, Somalia and Arabia plates. It is the volcanic activity along the edges of the plates that is causing this phenomenon. The point where the three plates meet is pulling apart at a constant rate: about the speed your finger nails grow, a couple of centimetres a year. This creates a rift. However, this central point where the plates meet is stuck together and the area around the rift stretches like an elastic band for hundreds of years. Eventually it breaks, and the plates move apart very quickly, like the dramatic events people saw in 2005.  Scientists think that the intrusion of new molten rock (magma) is the trigger for the rift to break – a bit like if you put a small cut in the elastic band. If magma is present it can force the tectonic plates to pull apart, and this magma sometimes appears at the surface through volcanic eruptions.

Figure 1. Two models showing how the continental lithosphere expands. The lithosphere comprises the crust and the portion of the upper mantle that behaves elastically.

Figure 1. Two models showing how the tectonic plates split apart. In a) an ocean forms as the plates pull apart. In b) magma is forcing the plates apart, forming new land.

Figure 2. Models showing continental break-up leading to the formation of a volcanic passive margin – a transitional crust that occurs as the result of the formation of ocean basins via continental rifting.

Figure 2. Models showing how tectonic plates can pull apart from each other, leaving a ridge of volcanoes in between them.

Why is this important?

 

 

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With thanks to Cynthia Ebinger and the British Geophysical Association for permission to reproduce the figures.