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Earth’s outermost layer—the crust—is constantly renewing itself. It’s broken into giant chunks called tectonic plates that pull apart, push against or slide past one another, creating grand geologic features.
Underwater mountain ranges, or mid-ocean ridges, for instance, generally take shape where two tectonic plates are moving away from each other. Magma can then bubble up in between, solidifying and turning into new oceanic crust as part of a process called seafloor spreading. Although the phenomenon has created entire ocean basins, it remains quite mysterious because it happens so deep in the water.
Now, for the first time, scientists have observed this dynamic activity happening in real time. They describe their findings—and their stroke of luck—in a study published July 8 in the journal Nature, shedding light on a mechanism that made roughly two-thirds of Earth’s crust.
“We still know remarkably little about the frequency, magnitude and dynamics of the eruptions and tectonic processes that build [mid-ocean ridges],” Isobel Yeo, a geoscientist at the National Oceanography Center, a nonprofit in the United Kingdom, who did not participate in the study, tells Davide Castelvecchi at Nature.
In February 2024, the research team behind the new study traveled by ship to the southern Indian Ocean, where the Southeast Indian Ridge sits on the border between two tectonic plates that travel away from each other by about 2.4 inches per year. There, they deployed a bevy of scientific instruments on the seafloor, including acoustic beacons and underwater microphones to detect sound waves, acoustic sensors that pick up on seafloor movement, and a pressure gauge.
Then, they waited—but not for long.
On April 26, 2024, a series of earthquakes struck, marking the beginning of a seafloor spreading event. “We have been very lucky to have had all these instruments set up when it happened,” study co-author Jean-Yves Royer, a marine geophysicist at the French National Center for Scientific Research, tells the New York Times’ K.R. Callaway. “But also, we are lucky because these big piles of lava outpoured one or two kilometers [around a mile] away from our instruments, so we didn’t lose any data.”
Across six days, the seafloor dropped by about 13 feet, the team found. And overall, the tectonic plates moved apart by at least 6.5 feet. Both numbers came as a surprise. “We were expecting to measure a few centimeters of horizontal displacement and maybe a few centimeters of vertical displacement,” Royer tells Scientific American’s Sam Macdonald.
Mapping of the bottom of the ocean before and after the event suggests that around 5.7 billion cubic feet of lava—roughly 65 times the volume of the Great Pyramid of Giza—emerged in about 16 days to form a new seafloor. Computer simulations suggest that the event primarily happened because magma was pushed upward through cracks in the crust, driven by the emptying of an underground reservoir of the molten rock.
What’s more, the detected earthquakes didn’t seem powerful enough to be responsible for the observed horizontal changes, supporting the idea that most tectonic plate movement at mid-ocean ridges does not create seismic activity. The work also suggests that at these plate boundaries, quiet stretching continues until stress builds up enough to trigger a sudden seafloor spreading event.
“It’s quite difficult, and perhaps rare, to make these measurements,” Aaron Micallef, a marine geologist at the Monterey Bay Aquarium Research Institute who did not participate in the study, tells the Times. “We know so little about what’s going on in these settings that we’re not even really sure of what measurements we need to carry out, so that’s why it’s very useful to throw all the instruments that you have at the problem, as these researchers have done.”
This article was originally published on Smithsonian Magazine. Read the full story here: In a First, Scientists Witness the Seafloor Spread in Real Time, Giving Them a Rare Glimpse at a Mysterious Geologic Process © 2026 Smithsonian Institution.
