Water deep below the surface of the Earth triggers earthquakes and tsunamis by lowering the melting point of rocks along fault lines, a new study reveals.
UK scientists say they’ve found a correlation between water release data and levels of seismic activity along the Caribbean-American tectonic plate border.
This process occurs in subduction zones, where the Earth’s tectonic plates converge and one plate sinks beneath another.
These zones, which have been described as the ‘biggest crash scenes on Earth’, pass large volumes of water in and out, mainly through volcanic eruptions.
The research team say they’ve provided the first conclusive evidence directly linking deep Earth’s water cycle with magma production and earthquake activity.
Research focused on the Atlantic plate, and more specifically, the Lesser Antilles volcanic arc, located at the eastern edge of the Caribbean Sea, which forms the eastern boundary of the Caribbean Plate. Pictured, Quill, on the island of Statia – one of the islands in the Lesser Antilles
‘As plates journey from where they are first made at mid-ocean ridges to subduction zones, seawater enters the rocks through cracks, faults and by binding to minerals,’ said Dr George Cooper at the University of Bristol’s School of Earth Sciences.
‘Upon reaching a subduction zone, the sinking plate heats up and gets squeezed, resulting in the gradual release of some or all of its water.
‘As water is released it lowers the melting point of the surrounding rocks and generates magma.
‘This magma is buoyant and moves upwards, ultimately leading to eruptions in the overlying volcanic arc.
These eruptions are potentially explosive because of volatile chemicals dissolved in the magma, he said.
‘The same process can trigger earthquakes and may affect key properties such as their magnitude and whether they trigger tsunamis or not.’
The Lesser Antilles volcanic arc, part of a subduction zone, is marked in red. It’s a region of seismic activity, running along the Caribbean-American tectonic plate border
Subduction zones, where tectonic plates converge and one plate sinks beneath another, are the most important parts of the cycle – with large volumes of water going in and coming out, mainly through volcanic eruptions
Water (H2O) and other volatile chemicals – those that readily turn to vapour, such as carbon dioxide and sulphur – are cycled through the deep Earth.
These chemicals have played a key role in the evolution of our planet, including the formation of continents, the onset of life, the concentration of mineral resources and the distribution of volcanoes and earthquakes.
Exactly where and how volatiles are released and how they modify the host rock remains an area of intense research, according to the researchers, who form a project called Volatile Recycling in the Lesser Antilles (VoiLA).
The project brings together geophysicists, geochemists and geodynamicists from universities in the UK, France and Germany, as well as London’s Natural History Museum.
Bound by wild desire: Earth’s ‘Ring of Fire’
Earth’s so-called ‘Ring of Fire’ is a horseshoe-shaped geological disaster zone that is a hot bed for tectonic and volcanic activity.
The seismic region stretches along the Pacific Ocean coastlines, where the Pacific Plate grinds against other plates that form the Earth’s crust.
The 25,000-mile ring loops from New Zealand to Chile, passing through the coasts of Asia and the Americas on the way.
The region is susceptible to disasters because it is home to a vast number of ‘subduction zones’, areas where tectonic plates overlap.
Most studies have focused on subduction along the ‘Pacific Ring of Fire’ – a horseshoe-shaped seismically active belt that spans New Zealand, the east coast of Asia and the west coast of the Americas.
It’s along the Ring of Fire that the edge of one particular tectonic plate – called the Pacific Plate – meets other tectonic plates and causes tremors.
Around 90 per cent of the world’s earthquakes and 81 per cent of the world’s largest earthquakes occur along the Ring of Fire, according to the United States Geological Survey.
However, this new research focused on the Atlantic plate, and more specifically, the Lesser Antilles volcanic arc, located at the eastern edge of the Caribbean Sea.
It is part of a subduction zone where the crust of the South American Plate is being subducted under the Caribbean Plate.
‘This is one of only two zones that currently subduct plates formed by slow spreading,’ said Professor Saskia Goes at the Imperial College London.
‘We expect this to be hydrated more pervasively and heterogeneously than the fast spreading Pacific plate, and for expressions of water release to be more pronounced.’
The scientists collected data over the course of two marine cruises on the RRS James Cook, the 300-foot-long research vessel operated by the Natural Environment Research Council.
Data was gathered from temporary deployments of seismic stations that recorded earthquakes beneath the islands, geological fieldwork, chemical and mineral analyses of rock samples and numerical modelling.
To trace the influence of water along the length of the subduction zone, the scientists studied boron compositions and isotopes of melt inclusions – tiny pockets of trapped magma within volcanic crystals.
A map showing tectonic plates within the Caribbean region and the plate boundary zones between the Caribbean Ocean Plateau (the stable portion of the Caribbean plate) and its surrounding plates. The Lesser Antilles volcanic arc, located at the eastern edge of the Caribbean Sea, where the South American Plate is being subducted under the Caribbean Plate. Red arrows indicate the movement of the plate
These boron ‘fingerprints’ revealed that the water-rich mineral serpentine, contained in the sinking plate, is a dominant supplier of water to the central region of the Lesser Antilles arc.
‘By studying these micron-scale measurements it is possible to better understand large-scale processes,’ said co-author Professor Colin Macpherson at Durham University.
The data provided ‘the clearest indication to date’ that the structure and amount of water of the sinking plate are connected to seismic hazards of the Lesser Antilles volcanic arc.
The wettest part of the downgoing plate – the plate that moves under the other in the process of subduction – had major cracks, or fracture zones.
Tectonic plates collide to form the continents that we live on. Faults, such as the San Andreas (pictured) are directly related to the movement of tectonic plates
‘By making a numerical model of the history of fracture zone subduction below the islands, we found a direct link to the locations of the highest rates of small earthquakes and low shear wave velocities – which indicate fluids – in the subsurface,’ said Professor Goes.
The history of subduction of water-rich fracture zones can also explain why the central islands of the arc are the largest and why, over geologic history, they have produced the most magma.
‘Our study provides conclusive evidence that directly links the water-in and water-out parts of the cycle and its expressions in terms of magmatic productivity and earthquake activity,’ said Dr Cooper.
‘This may encourage studies at other subduction zones to find such water-bearing fault structures on the subducting plate to help understand patterns in volcanic and earthquake hazards.’
Researchers now want to learn more about how a pattern of water release could act as a ‘warning system’ for larger earthquakes and possible tsunamis.
The study has been published in Nature.
The Earth is moving under our feet: Tectonic plates move through the mantel 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 molded 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.