The Atlantic Ocean could be SWALLOWED by a terrifying 'Ring of Fire', scientists say as they discover a 'sleeping' subduction zone beneath the Gibraltar Strait

Although it may seem like an eternal feature of Earth, the Atlantic Ocean could be swallowed by a vast subduction zone, dubbed the 'Ring of Fire', a new study warns. 

Scientists in Portugal say this subduction zone is currently located beneath the Gibraltar Strait, the narrow gap of water between Spain and Morocco.

But the experts think it could grow and expand westwards into the Atlantic and eventually become responsible for a 'closing' or shrinking of the ocean basin. 

This will happen 'soon' in geological terms – in approximately 20 million years – at a time when humans could still be alive on the planet. 

Subduction zones are locations on Earth where one tectonic plate dives below the other, and are known for powerful seismic activity. 

It's well known that Earth's lithosphere (its rocky, outermost shell) is formed of around 15 tectonic plates, each of different shapes and sizes. Powerful seismic activity can be detected along the tectonic plate's borders, where the plates rub up against each other. This diagram shows tectonic plate boundaries with newly formed crust in red

The Strait of Gibraltar is between the countries of Spain (north) and Morocco (south). This 10-mile strait that separates the two countries (as well as Europe and Africa) is where two major tectonic plates (the Eurasian Plate and the African Plate) collide

The new study has been led by João Duarte, a professor in tectonics at the Faculty of Sciences of the University of Lisbon, Portugal. 

He and his colleagues warn that entire oceans can close up if new 'subduction zones' form – and this process may have already started with the Atlantic. 

'We have good reason to think that the Atlantic is starting to close,' Professor Duarte told MailOnline.  

'Subduction zones are what cause the oceans to close, by pulling their ocean floor back into the mantle, bringing the continents together.' 

The 10-mile Gibraltar Strait that separates Spain and Morocco (as well as Europe and Africa) is where two major tectonic plates meet – the Eurasian Plate and the African Plate. 

In this subduction zone, the African plate is subducting below the Eurasian plate, resulting in seismic activity and the risk of earthquakes.

Currently, the subduction zone below the Gibraltar Strait is 'sleeping', meaning the velocity at which the plate is sliding down into the Earth's mantle is 'very very slow'. 

Professor Duarte and colleagues say subduction zones can grow so that they enter another part of the ocean – a process dubbed 'subduction invasion'.

In subduction zones, the Earth's tectonic plates converge and one plate sinks beneath another (pictured) 

Map highlighting the Atlantic subduction zones, the fully developed Lesser Antilles and Scotia arcs on the western side and the Gibraltar arc on the eastern side

READ MORE: Nearly 75% of US now at risk of damaging earthquakes 

Scientists updated the National Seismic Hazard Model with new data 

Currently, the subduction zone below the Gibraltar Strait is about 125 miles long (although it plunges up to a depth of more than 350 miles), making it one of the smallest subduction zones in the world. 

But 20 million years from now, it could reach a length of about 500 miles, Professor Duarte said. 

For the study, the team used computer modelling to simulate the life of the subduction zone since its birth during the Oligocene epoch (34 million to 23 million years ago). 

Modelling its fate into the future, they found it will move westwards through the narrow Gibraltar Strait over the next 20 million years. 

The model predicts that the extended subduction zone will form a new Atlantic subduction system – the so-called 'Ring of Fire', named after the Pacific Ocean version that already exists. 

Subduction slowly pulls the ocean floor under, dragging the continents closer together as the ocean basin shrinks. 

Therefore, this new Ring of Fire could 'close up' the Atlantic, making it cease to exist – albeit in an estimated 20 million years. 

'The results suggest that the arc will propagate farther into the Atlantic after a period of quiescence,' the team say in their study, published in the journal Geology. 

Maps showing the evolution of the Gibraltar subduction zone from 30 million years ago to 50 million years into the future

'The models also show how a subduction zone starting in a closing ocean can migrate into a new opening ocean through a narrow oceanic corridor. 

'Subduction invasion is likely a common mechanism of subduction initiation in Atlantic-type oceans and a fundamental process in the recent geological evolution of Earth.' 

The finding that the Gibraltar subduction is still currently active also has important implications for seismic activity in the area. 

Events such as the 1755 Great Lisbon Earthquake are a reminder of the existing seismic threat and require 'preparedness'. 

The historic event – with an estimated magnitude of 7.7 – killed around 12,000 and almost completely destroyed Lisbon and adjoining areas. 

The Earth is moving under our feet: Tectonic plates move through the mantle and produce Earthquakes as they scrape against each other

Tectonic plates are composed of Earth's crust and the uppermost portion of the mantle. 

Below is the asthenosphere: the warm, viscous conveyor belt of rock on which tectonic plates ride.

The Earth has fifteen tectonic plates (pictured) that together have moulded the shape of the landscape we see around us today 

Earthquakes typically occur at the boundaries of tectonic plates, where one plate dips below another, thrusts another upward, or where plate edges scrape alongside each other. 

Earthquakes rarely occur in the middle of plates, but they can happen when ancient faults or rifts far below the surface reactivate. 

These areas are relatively weak compared to the surrounding plate, and can easily slip and cause an earthquake.