What Did Scientists Find Under the Ocean Near Mayotte in 2018?

A Hidden Volcano and a Mineral from Earth’s Deepest Past

In 2018, scientists discovered a brand-new submarine volcano named Fani Maore rising roughly 800 metres from the seafloor east of Mayotte, and analysis of its lava revealed traces of bridgmanite — a mineral that forms only under extreme lower mantle pressures — making it the first time this mineral had ever been detected in surface volcanic rocks.

The Earthquakes That Started It All

In May 2018, a swarm of earthquakes began rattling the French island of Mayotte in the Indian Ocean. The largest earthquake ever recorded in the region struck first, alarming residents and baffling seismologists. No obvious geological explanation was immediately available. The seismic activity was unlike anything in the region’s recorded history, and scientists scrambled to understand its source.

Then, on November 11, 2018, something even stranger happened. A low-frequency seismic pulse — slow, rhythmic, and eerily uniform — rippled silently around the entire planet. Instruments from Chile to Canada to Kenya detected it. Seismologists were at a loss. The signal matched no known earthquake signature, no known volcanic tremor pattern. It circled Earth for over twenty minutes. For months, it had no accepted explanation.

What the Seafloor Survey Revealed

In May 2019, the French research vessel Marion Dufresne conducted a detailed survey of the seafloor approximately 50 kilometres east of Mayotte. What the team found was extraordinary: a massive new underwater volcano had formed — silently, invisibly, in complete darkness — sometime during the preceding months of seismic chaos. Fani Maore, as it was named, stood roughly 800 metres tall with a base diameter of several kilometres, making it one of the largest submarine volcanic structures ever observed forming in real time. Scientists estimate that more than five cubic kilometres of magma had erupted to construct it — a staggering volume released with no direct human observation.

The seafloor around it bore the marks of intense geological upheaval: lava flows, collapsed terrain, and evidence of one of the most significant submarine eruptions in modern recorded history.

Bridgmanite: A Mineral That Should Not Be There

When researchers analyzed lava samples collected from Fani Maore, they made a discovery that genuinely stunned the geological community. The lava contained traces of bridgmanite — Earth’s most abundant mineral by volume, yet one that exists only under the crushing pressures found in the lower mantle, at depths below roughly 660 kilometres. Under normal conditions, bridgmanite cannot survive the pressure drop as magma rises toward the surface. It transforms into other minerals long before reaching the seafloor.

Yet here it was, preserved in microscopic inclusions within the Fani Maore lava. This suggested the magma had carried material upward so rapidly, or under such unusual conditions, that fragments of lower mantle rock were preserved intact. More remarkably, geochemical analysis indicated that this material bore a chemical signature consistent with some of the oldest reservoirs in Earth’s mantle — material that may have remained largely undisturbed since the planet’s earliest geological era, billions of years ago.

Why This Discovery Matters

Fani Maore is not just a geological curiosity. It represents a rare window into Earth’s deep interior that scientists almost never get to observe. Most of what we know about the lower mantle comes from seismic imaging and laboratory experiments replicating extreme pressures. Having actual physical samples carrying lower mantle signatures — delivered to the seafloor by a newly born volcano — is exceptional.

The discovery also raises profound questions about how and where deep mantle plumes originate, how quickly magma can ascend from extraordinary depths, and what other ancient chemical reservoirs remain locked inside Earth, untouched since the planet’s formation.

The ocean floor is still writing chapters of Earth’s history that we have barely begun to read.