Scientists have captured, for the first time, a real-time recording of the ocean floor as it splits apart along a deep-sea ridge, triggering a massive lava flow and reshaping a stretch of seafloor within about two weeks.
The discovery, published in the journal Nature, gives researchers a rare look at how new ocean crust forms and why undersea faults produce far fewer earthquakes than expected.
The event took place along the Southeast Indian Ridge, a boundary between tectonic plates in the Southern Indian Ocean near Amsterdam Island.
A team led by Jean-Yves Royer of Geo-Ocean, a joint research unit of CNRS, the University of Brest, and Ifremer in France, had installed a network of underwater instruments across the ridge in late February 2024.
The equipment included hydrophones, seafloor sensors and a pressure recorder, all meant to track subtle shifts in the seabed. Two months later, on April 26, the ocean floor gave them exactly what they were watching for.
Ocean floor splits apart as quakes race along the ridge
That evening, a swarm of small earthquakes broke out along the ridge and quickly spread in two directions, racing outward at roughly 2 to 3 meters per second (6.6 to 9.8 feet per second).
Within hours, seismic sensors detected more than 30 quakes, including several stronger than magnitude 5. As the shaking spread, the seafloor itself began to sink.
For the first time, researchers filmed the ocean floor splits apart at a deep-sea ridge, offering new clues about undersea earthquakes. pic.twitter.com/cDvtfEfq8E
— Tom Marvolo Riddle (@tom_riddle2025) July 9, 2026
A pressure sensor recorded the valley floor dropping about 4 meters (13 feet) over six days, with most of that drop happening in the first 16 hours alone. At the same time, seafloor sensors on either side of the valley moved apart by more than a meter (more than 3 feet).
Royer and his colleagues concluded that the sinking and spreading were signs of an underground magma chamber emptying out as molten rock pushed upward and outward through cracks in the crust. That molten rock eventually reached the seafloor.
Magma drains away as new lava reshapes the seafloor
Follow-up mapping a year later showed new lava had piled up in some spots more than 90 meters thick (295 feet). In total, the eruption released about 160 million cubic meters (5.65 billion cubic feet) of lava over 16 days, roughly enough to fill 64,000 Olympic swimming pools.
The disturbance did not stay contained to the ridge. Within an hour, it set off strong earthquakes on two nearby fault lines, including a magnitude 5.9 quake, as stress from the spreading rock transferred outward.
Perhaps the most striking finding involves what did not happen. Despite the scale of the shifting, only about a quarter of the total movement along the faults showed up as detectable earthquakes.
The rest, roughly three-quarters, occurred quietly, without shaking. Royer’s team says this aseismic slipping likely explains a long-standing puzzle: why mid-ocean ridges move so much yet produce so little earthquake energy compared to what scientists would expect.
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