Far down on the ocean floor, Earth is recycling its own skin. At certain boundaries, the huge plates of rock that make up the planet’s crust crash into or over each other, pushing old crust below. At other junctures, these tectonic plates are spreading apart, allowing magma to bubble up and create entirely new stretches of seafloor.

But the process is subtle and difficult to catch in action. Typically, the seafloor only adds a few inches of new ground per year, unless prompted by sudden, unpredictable earthquakes and other large-scale interactions of the tectonic plates.

In 2024, however, researchers were able to observe for the first time a large-scale seafloor spreading event, in which a series of earthquakes abruptly added more than three feet of new seafloor to the Indian Ocean. Their findings, described in a study published on Wednesday in the journal Nature, offer a look at one of Earth’s most elusive processes.

“We have been very lucky to have had all these instruments set up when it happened,” said Jean-Yves Royer, a marine geophysicist and lead author of the study. “But also we are lucky because these big piles of lava outpoured one or two kilometers away from our instruments, so we didn’t lose any data.”

Dr. Royer and his colleagues had only recently begun a three-year experiment along the ridge between two of the Indian Ocean’s tectonic plates. The observatory they used, called OHA-GEODAMS, was made up of 15 monitoring stations that could sense sound waves traveling through the ocean from earthquakes and other geophysical changes at the seafloor. By good fortune, it was deployed just two months before the swarm of earthquakes in 2024.

The movement of Earth’s tectonic plates is noisy. The observatory detected not only the low-frequency rumblings of rocks but also the precise details of the motion: Part of the ridge collapsed by about 13 feet, and its two sides separated by more than three feet.

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