An international team of geophysicists examining the Southern Indian Ocean floor witnessed a section greater than two meters split apart, releasing millions of cubic meters of stored-up magma within just a few days.

Jean-Yves Royer, a marine geophysicist at the French National Centre for Scientific Research (CNRS) in Brest and a co-author of the study detailing the team’s serendipitous discovery, said witnessing the ocean floor splitting apart in real time was “a major surprise,” while the team hailed the scientific value of finally witnessing these processes up close.

Scientists Have Never Witnessed The Ocean Floor Splitting Apart in Real Time

Because the ocean floor is dynamic, the movement of tectonic plates pulling the existing crust away from mid-oceanic ridges allows magma to well up to the surface. When it dries, this material solidifies, adding to the existing crust. While scientists have understood this process for decades, no one has ever witnessed the phenomenon directly. This absence has left a gap in scientific knowledge that, as study co-author Isobel Yeo, a geoscientist at the National Oceanography Center in Southampton, UK, notes, persists to this day.

“We still know remarkably little about the frequency, magnitude, and dynamics of the eruptions and tectonic processes that build them”, the researcher explained

To try to fill that gap, the team focused its research on a section of the seafloor called the Southeast Indian Ridge, which runs east to west across the Indian Ocean. Due to its location, the ridge separates two tectonic plates, the Antarctic and the Australian.

The team notes that these two plates, which contain Antarctica and Oceania and the surrounding oceanic crust, are continuously moving in opposite directions by roughly six centimeters each year. Although both plates are exerting stress on the ridge, the team said the northward movement of the Australian plate accounts for most of this annual expansion.

The motion dynamics can also change by location. For example, one section of the Australian plate may stay stationary for a period and then suddenly experience a large surge in motion. These sudden events are accompanied by earthquakes. 

Ocean Floor Movement in Real Time

In hopes of catching the ocean floor splitting in real time, Royer and colleagues ventured to the Southeastern Indian Ridge in February 2024. Once on site, the team deployed three categories of sensors at several different locations along a 100-kilometer stretch of the ridge. The sensor array included five hydrophones that detect underwater sound, including the telltale sonic waves produced by earthquakes. The team also deployed 15 battery-powered acoustic beacons designed to emit and detect sounds at selected locations along the ridge.

Because the acoustic beacons can produce and receive sounds, the team programmed them to exchange audio signals every four hours. This regular exchange allowed the team to measure the time between sound and response, which they used to determine the distance between the two beacons at four-hour intervals.

After the sensors were all in place, the team’s efforts finally paid off. According to the study, the carefully placed hydrophones began to detect seismic tremors on the ocean floor. These signals were followed by several days of acoustic beacon returns, indicating some of the stations had moved. When the team calculated the time between beacon signals, they determined that some sections of the ocean floor had moved by “at least” two meters as they were pulled away from the ridge.

The team also found evidence that the ocean floor was splitting apart in real time, altering the ocean floor’s depth. According to a reading from a single pressure sensor, the depth change caused by the event was “substantial.”

a rare direct view of these processes in action

In the study’s conclusion, the research team estimates that 160 million cubic meters of lava rose between the split ocean floor and spilled onto the seafloor. They also suggested that the magma explosion emptied a reservoir that had accumulated along the ridge, which caused portions of the floor to “subside.”

Royer said the team was only expecting to find a vertical displacement of “a few centimeters.” Instead, he notes, “we measured 4.2 meters.” The team said this large amount of change suggests that three to six decades’ worth of stress from the northward movement of the Australian tectonic plate was released during the ocean-floor-splitting event.

When discussing the significance of witnessing the ocean floor splitting apart in real time for the first time, Yeo said their study “provides a rare direct view of these processes in action.”

The study “Anatomy of a seafloor spreading event captured by in situ seismogeodesy” was published in Nature.

 Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.

The continent of Africa is splitting into 2 tectonic plates in the middle of Ethiopia. In the recent past, geophysicists have improved their understanding of how tectonic plates like these separate. They’ve shown that continents begin to split apart as the crust and upper mantle, known as the lithosphere, crack and shift. Later, magma from deep within the Earth travels upward through these cracks to Earth’s surface, forming volcanoes. Therefore, scientists know that volcanoes form in areas of continental rifting, but not how quickly they form, which complicates efforts to assess volcanic hazards in rift zones.

Researchers led by Kevin Wong sought to answer this question by examining a mineral formed when magma cools, called olivine. They focused on 72 olivine crystals ranging in size from 1 to 4 millimeters (0.04 to 0.16 inches) from rocks collected at the Boku and Ziway volcanic fields in the Main Ethiopian Rift (MER) zone in Africa. They explained that the lithosphere in this area is still about 35 to 40 kilometers (21 to 25 miles) thick. This thick lithosphere suggests that the MER represents an intermediate stage of continental separation and offers a rare opportunity to study how tectonic stretching transitions into magmatic rifting in the process.

Wong and his team analyzed olivine because it’s one of the first minerals to crystallize from magma, and it continues to grow as the magma rises and cools. As magma rises, its composition changes, producing sharp chemical “zones” within the growing crystals, analogous to growth rings in trees. Changing temperatures and magma compositions cause different elements, like magnesium and iron, to diffuse into and out of the crystals at various rates during the magma’s ascent. So scientists can model these chemical zones and their boundaries in olivine crystals to determine how quickly the magma ascended from the upper mantle to erupt in the rift.

Wong and colleagues examined the olivine crystals from the MER volcanic fields using high-magnification imaging and chemical analyses, with an instrument known as an electron microprobe. Within each crystal, the team mapped 10 to 15 points spaced approximately 5 to 15 microns apart (about 10% of the thickness of a human hair) along a transect from the inner core to the outer rim, spanning its growth zones. 

They found 2 different populations of olivine crystals. The first consisted of normal-zoned crystals with magnesium-rich inner cores, and the second consisted of reverse-zoned crystals with lower magnesium cores. They explained that recently-formed magmas in the deep Earth contain higher amounts of the element magnesium relative to iron. The magnesium-rich zone has a sharp boundary with the magnesium-poor zone, but this boundary can get blurred when elements diffuse across it. Diffusion progressively smooths these crystal boundaries over time at known rates, so researchers can use their “blurryness” to extract information on how quickly the crystals equilibrated with the surrounding magma.

The researchers used numerical models to estimate how quickly magnesium and iron would diffuse across these chemical boundaries at different temperatures and surrounding magma chemistries. They compared thousands of simulated diffusion profiles to their measured olivine diffusion profiles. They used this iterative process to estimate that the crystals diffused, on average, for 40 and 17 days in the surrounding magma while ascending from the deep Earth to erupt at Boku and Ziway, respectively. They further tested these estimates using a growth-diffusion model that better represented natural crystal behavior. That model produced ascent times of about 27 days on average and better reproduced the crystal zoning patterns they observed.

Based on these models, the researchers concluded that intermediate-stage rifting events happen on unexpectedly short timescales. Magmas travel up to 40 kilometers (25 miles) from the deep Earth to the surface within, on average, a single calendar month, which is closer to human timescales than geologic timescales. They suggested that this rapid ascent is likely due to highly developed magmatic plumbing systems in the lithosphere that form before much lithospheric thinning. However, they noted that their results still suggest a wider range in ascension timescales than optimal for disaster mitigation and prediction. 

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