A seafloor spreading event, where magma rises from within to create new oceanic crust at mid-ocean ridges (MOR) that form about two-thirds of the Earth's surface, has been directly observed in the field for the first time.

A research team led by Professor Jean-Yves Royer of the University of Brest in France announced in the scientific journal Nature on July 9 that they have, for the first time in the world, directly observed the phenomenon of seafloor spreading, where new crust is formed, at the Southeast Indian Ridge in the Indian Ocean.

The research team stated, "We have directly observed the entire process of a seafloor spreading event at a mid-ocean ridge in the field for the first time," adding, "This will be a significant turning point in understanding the process of oceanic crust formation and the mechanism by which deformation energy is released at plate boundaries."

A mid-ocean ridge is a vast underwater mountain range where magma rising from the Earth's interior cools to create new oceanic crust.

At the Southeast Indian Ridge in the Indian Ocean, the Australian Plate and the Antarctic Plate are moving away from each other at a rate of approximately 6.2 cm per year as new seafloor crust is formed.

The research team pointed out that while it has been estimated that such plate movements do not occur steadily little by little each year, but rather involve deformation energy accumulating over decades and then being released all at once over a short period, this phenomenon had not been directly confirmed until now.

In February 2024, the research team installed underwater acoustic sensors, seafloor distance measuring equipment, and seafloor pressure gauges at the Southeast Indian Ridge and the nearby Amsterdam Transform Fault.

The team stated that they were fortunate to record the entire process of new oceanic crust formation in real-time when a seafloor spreading event occurred, accompanied by a series of earthquakes, on April 26, 2024, just two months after installing the observation equipment.

Observations showed that the seafloor spreading began as earthquakes occurred in succession along the ridge.

Subsequently, magma from underground split the rock to create dykes and spread in both directions. During this process, the seafloor above the underground space where the magma had escaped subsided by more than 4 meters, while at the same time, the seafloor spread apart by more than 1 meter on both sides.

The research team explained that they observed the process of the seafloor subsiding by a total of 4.2 meters over 6 days for the first time in real-time, noting that the seafloor movement speed reached approximately 5 cm per minute immediately after the earthquake, but gradually slowed down to a level of 1.2 cm per day over time.

They analyzed that the pressure dropped as magma escaped from a large magma reservoir, approximately 2.5 km wide and located about 3.6 km below the crust, and that the seafloor subsided as this magma moved through the newly formed gaps along the ridge.

The team also explained that the seafloor spread horizontally by a total of about 2.4 meters, which corresponds to the deformation that would occur over approximately 38 years if the plates were spreading little by little at the current rate, all occurring in just 6 days.

The magma that rose along the dykes erupted and poured out a total of 160 million cubic meters of lava over approximately 16 days, forming a large-scale lava flow about 4 km in length, with some areas found to have lava thicknesses exceeding 90 meters.

The research team stated that model analysis results showed that approximately 76% of the fault slip occurred without earthquakes, while only 24% was caused by earthquakes, adding that this could be a clue to explaining the seismic deficit phenomenon, where there is little earthquake activity even when plates spread rapidly.

They further added that these research results provide a more comprehensive picture of how mid-ocean ridges operate when seafloor spreading events occur over short periods, suggesting that such events may be a process of releasing deformation energy that has accumulated over decades along plate boundaries.

(Photo: Provided by Nature, Jean-Yves Royer et al., Yonhap News)