Under the Microscope: What will the Earth's tectonic plates do next?
Monday 28 June 2010
Asked by: Stephen Ward, Poole
Answered by: James Hammond, research associate at the Centre for the Department of Earth Sciences at Bristol University
Ethiopia on the move
The Earth is made up of many tectonic plates, and these are constantly shifting around on the Earth's surface. It used to be one big land mass and one big ocean, but they split apart millions of years ago.
In East Africa, we're actually on the brink of a new split. There are several rifts in the Earth's surface in Africa: the Red Sea rift, the Gulf of Aden, and the East African rift. These all meet in the Afar region of Ethiopia.
In September 2005, a 60km sheet of magma was injected in the crust in this region, pushing it apart up to 8m in some places. The unique thing about the region is that now we're actually able to look at the early stages of ocean-floor formation – we are really seeing how a new crust is created when two plates move apart.
It's the breaking apart of a continent, and the forming of a new continent. This process has been going on for the past 30m years, but the actual process where the continents split really happens very rarely.
The movement of the Somalia plate
Much of the Afar region is below sea level anyway, with the sea only kept at bay by a small area of land in Eritrea. So we expect that at one of these rift events in the future the new area will go completely below sea level and the Red Sea will rush in. There will be many similar rift events in the region – there have already been 14 smaller ones since the first observed event in 2005.
The whole Afar area is underlain by large amounts of magma, and even a lava lake. Every few hundred years or so the magma will inject itself into the crust, which will cause the ground to shift significantly. The Somalia plate on the east side will eventually drift off and the sea will move in. This will take about 5m to 10m years.
It's very hard to predict what will happen when it does split – it's a very dynamic system. When India collided with the Himalayas 50m years ago, for example, it caused all the plates to shift around. But the African plate isn't moving much. We think the Somalia plate will just drift off east into the Indian Ocean.
Rifts around the world
There are many rifts in the world – the Rio Grande rift in the United States, for example – but this one is at a particularly late stage. The Earth is shifting all the time, the tectonic plates are continually moving, but what's unique about this is that it's so magma-rich, so we're actually seeing new ocean floor forming.
A rift event like this also happened in Iceland in the 1970s, when sheets of magma were injected into the Earth's crust. But this is the first time that it has happened when we've had all the modern technology and recording equipment now available to us – things like satellites so that we can get aerial views – which is why it really is so important. The international scientific community is very much working collaboratively on it.
What's occurring in the Afar region is very similar to the process that would have happened around 65m years ago, when the UK, Greenland and Canada split apart. The only way scientists had been able to understand this phenomenon is to look at what happened 65m years ago. So it's a nice, now, to be able to actually walk about on it – in Africa, you can see it and study it while it's happening. It's like being able to walk around on the Mid-Atlantic ridge, but it's on land so you can walk around and monitor it without having to go underwater!
The scientific importance of the African split
Some of the questions for scientists researching tectonic shifts have been: "Do you need a lot of magma to cause these shifts? Or do the plates just drift apart?" We didn't know if it could just be the plate-tectonic forces that drive the drift, or whether you need something else to lubricate it or to facilitate the split.
We're seeing that, in this region of Africa, it is really driven by the deep magma, hundreds of kilometres under-ground. It's that material coming up that pushes the surface apart. From studying this rift, we now think it is the magma flux that drives it.
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