Hidden beneath the waters of the Strait of Gibraltar, a gigantic ocean trench lies in apparent sleep. But don't be fooled by its calm: according to a team of geologists, this "dormant" subduction zone could reawaken in the distant future. And unleash a process capable of distorting the geography of our planet.
We are talking about the "subduction invasion" of the Atlantic Ocean, a phenomenon that could lead to the formation of a new "ring of fire" similar to the one surrounding the Pacific, and to the slow disappearance of the Atlantic itself.
A giant dozing at the bottom of the sea
The Gibraltar Arc, also known as the Gibraltar Trench, is a huge scar on the Earth's crust hundreds of kilometers long and up to 5.000 meters deep. An area of subduction which runs along the border between the African and Eurasian plates. Here, denser oceanic crust sinks into the mantle, in a process that is usually accompanied by earthquakes, volcanic eruptions and the formation of mountain ranges.
Over the last 5 million years, this giant seems to have fallen asleep. The absence of strong seismic and volcanic activity in the area made many scientists think that the Gibraltar Trench was now “dead”, unable to influence the geological fate of the region. Now, however, a new study published on Geology (I link it here) suggests that the monster of Gibraltar is just taking a nap, ready to awaken in the not too distant future (in geological terms, of course).
Westward, into the unknown
The team led by João Duarte of the University of Lisbon has in fact discovered that the Gibraltar arc is slowly moving westwards, getting dangerously close to the "edge" of the Atlantic Ocean. Using sophisticated computer models, the researchers simulated the evolution of the subduction zone from its “birthday,” about 30 million years ago, up to 40 million years into the future.
The results? Relatively disturbing: After a period of stagnation lasting 5 million years, the Gibraltar Trench could resume its westward march in about 20 million years, “invading” the Atlantic in a process known as “subduction invasion”. In practice, the monster will awaken from its torpor to slowly devour the ocean floor, causing the crust to sink into the earth's mantle.
Gibraltar, a new ring of fire (for a lot of trouble)
According to the study, the invasion of the Atlantic by the Gibraltar arc could trigger the formation of a subduction system similar to the infamous "Ring of Fire" surrounding the Pacific Ocean. This ring is responsible about 90% of the world's earthquakes and hosts over 75% of the active volcanoes on Earth.
Now imagine a similar scenario, but in the Atlantic. With subduction zones chewing up oceanic crust on both sides of the ocean, the Atlantic would begin to shrink, eventually closing entirely in the distant future. Goodbye to transatlantic cruises, welcome to the era of the Americas colliding with Africa and Europe. A real nightmare for geographers (and for shipping companies, if they still existed, which allow me to doubt).
But why should the Gibraltar arc awaken in 20 million years?
According to the authors of the study, the reason is to be found in his current "pause for reflection". Over the past 5 million years, the trench's movement has nearly stopped, explaining the lack of major earthquakes and volcanoes in the area.
As mentioned, this does not mean that the monster of Gibraltar is dead. On the contrary. He's just accumulating energy, like a giant catching his breath before moving on again. And when it wakes up, it could do so with renewed vigor, pushing inexorably westwards until it "crashes" against the Atlantic seabed. At that point, subduction will be unstoppable.
A look into the (very distant) future
None of us will see the Atlantic close or the Americas collide with Africa (unless sensational discoveries are made on immortality). But this doesn't make the scenario any less fascinating or any less disturbing.
Duarte and colleagues' research reminds us that our planet is constantly changing, subject to titanic forces that act on time scales that are difficult for the human mind to conceive. What seems immutable today, such as the shape of the continents or the vastness of the oceans, is actually just a snapshot in a film billions of years long.
Perhaps, in a few million years, our descendants (or the robots that will have replaced them) will look at the maps of the "old world" with the same curiosity with which we look at the continents of the Triassic or Jurassic. And they will wonder how people lived on that strange Earth, where the Atlantic separated two continental masses destined to become one.
