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Forcing the Earth into shape

“Whilst we know a great deal about where the tectonic plates have moved, we know little about the forces that contribute to these shifts,” says Giampiero Iaffaldano from the Research School of Earth Sciences. “These forces are responsible for deformation of the Earth’s crust, the rise of large mountain ranges and the seismic behaviour at plate margins, so it is of paramount importance to understand their magnitude.”

The theory of plate tectonics presented in the 1960s revolutionised Earth sciences. After the overturning of the ‘fixist’ position on the movement of the Earth’s crust (which stated that the Earth’s crust was ‘fixed’ in its current state), Earth scientists were able to soon begin explaining a diverse range of geological phenomena, including earthquakes, volcanic eruptions and the creation of mountain ranges.

Plate tectonic theory says that the 100km thick outer shell of Earth, the lithosphere, is divided into pieces called tectonic plates. Plates move in different directions at speeds in the order of centimetres per year, comparable to the speed of fingernail growth in humans. At times these movements speed up and slow down, and often plates will jolt suddenly at their borders, creating geological events such as earthquakes.

Yet, despite what we know about the movement of the plates we still struggle to understand the forces behind these shifts. This is something that Iaffaldano is aiming to find out. “The forces that shift the plates are varied. Research shows that there are a number of factors that may lead to an increase or decrease in the movement of the Earth’s plates. It is a very complicated process.”

For example, looking at the border between the Nazca and South American plate shows that there are significant forces below the Earth’s crust, which are behind the shaping of the Earth’s plates. In this research Iaffaldano, working with colleagues from Italy and Germany, showed that there was a significant exchange of force between the two plates, which is what creates the strange curved nature of their boundary.

“We focused on a particular plate margin, one that exhibits an unusual curved shape. One can actually see it on a globe, in the shape of the Andes. This curvature holds information on the magnitude of forces acting upon tectonic plates, generating their motions,” Iaffaldano said. “Using simple laboratory experiments that mimic plate motions, we found that in order to create that peculiar curvature, the Nazca and its neighbour plate would have to have exchanged at least 20 per cent of the force driving their relative motion. This is a significant level of force exchanged.’’

“We still have a way to go. With more research, and more time, however, I am certain that we will soon be able to understand what it is that makes the plates move. This will have a huge impact on our understanding of geological events, such as earthquakes and mountain building,” Iaffaldano concluded.

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About Simon Copland

Simon Copland is a freelance writer and climate campaigner. In his spare time he plays rugby union and is a David Bowie fanatic. He is a regular columnist for the Sydney Star Observer, blogs at The Moonbat and tweets at @SimonCopland.

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