How were the mountains formed in the Iberian Peninsula?
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One day in 2011, in a laboratory in Amsterdam, a group of scientists went back 55 million years, took the Iberian Peninsula and stamped it against what is now France. By that time, erosion had turned the peninsula into an almost smooth table, but when what is now Spain collided with what was then the southern tip of Eurasia, scientists saw the Pyrenees, the Cantabrian Mountains, the Sistema Central and Sierra Morena like the one who does a Michael Jackson-like dancemoonwalk step on a carpet and sees how the wrinkles get steeper. A video now shows this process, which lasted 35 million years, in just half a minute.
For three years, scientists made 21 Iberian peninsulas, with sand and a silicone similar to the one that some women graft on their breasts. "We did the Iberian Peninsula over and over again," recalls Javier Fernández Lozano, one of the geologists at the Amsterdam lab. When they had a new Iberian peninsula ready, the size of a chessboard, they subjected it to a force equivalent to that generated after the clash between the masses that today are Spain and France.
The relief of the Iberian Peninsula, seen from space. / NASA Their goal was to solve a geological puzzle. If the Iberian Peninsula is observed from space, a pattern is easily detected in the western part: the Cantabrian Mountains, the Central System and Sierra Morena appear as three waves in a sea of land, separated by 300 kilometers from each other. In the east, that order is unraveling, with the Iberian system at the head. "We wanted to know why the western part has a periodic pattern and to the east that pattern disappears," explains Fernández Lozano, from the Faculty of Geological Sciences at the Complutense University of Madrid.
Hot and cold custard
The key is in the lithosphere, the most superficial layer of the Earth, which includes the six continents. The lithosphere floats on another fluid layer, located more than 250 kilometers deep, which allows the continents to dance. The human being has managed to travel to the Moon, 400,000 kilometers away, but he barely knows how what is under his feet works. "Very little is invested in the Iberian Peninsula to find out what is happening in the lithosphere," lamented Fernández Lozano. To complete other techniques used to study the interior of the Earth (such as the analysis of Earth's gravity or seismic waves), his team opted to make scale models.
None of its replicas of the Iberian Peninsula was the same as the others. Geologists played with the ingredients to change their conditions of density and viscosity, until the deformation formed before their eyes a relief similar to that of the Iberian Peninsula. So, they were able to extrapolate and draw conclusions. “In the Iberian Peninsula two lithospheres with different behaviors can be distinguished. Let's say that about 50 million years ago the western part of the peninsula was like cold custard, while the eastern part would resemble hot custard. When applying the deformation, each part behaved in a different way”, illustrates the geologist.
In the west of the peninsula, the tectonic forces were more effective and could travel more kilometers because the rocks were older and colder and, therefore, more resistant. However, this one was very different. There the lithosphere was weaker and hotter, since in the age of the dinosaurs the magma had risen from the deep layers of the Earth's interior. “It was easy to deform”, summarizes Fernández Lozano. The geologist and his colleagues have published these conclusions in the specialized journal Tectonics.
Scientists have condensed 35 million years of prehistory into just half a minute of video
Creating each of the scale models required a month of work in the laboratory of Dimitrios Sokoutis at the Free University of Amsterdam. Gerardo de Vicente, from the Complutense University of Madrid, also participated. Geologists used what little is known about the lithosphere of the Iberian Peninsula to produce faithful replicas. Each model was then deformed in slow motion for about 17 hours, the equivalent of about 40 million years. In an accelerated video, barely half a minute long, the result of three years of research can be seen.
Only on one occasion did one of the models fall to the ground and burst, ruining weeks of work. "Spain fell out of our hands, as it happens to politicians," jokes Fernández Lozano.