TEMPO.CO, Jakarta - Scientists have uncovered an unusual geological feature hidden deep beneath the Atlantic Ocean near Bermuda: a rock layer far thicker than anything previously observed beneath oceanic crust elsewhere on Earth.
The discovery reveals an extra rock layer measuring about 12.4 miles (20 kilometers) thick embedded beneath the ocean crust below Bermuda. Normally, Earth’s structure beneath the oceans is relatively simple, with the oceanic crust sitting directly atop the mantle.
“Typically, you have the bottom of the oceanic crust and then it would be expected to be the mantle,” said William Frazer, the study’s lead author and a seismologist at Carnegie Science in Washington, D.C., as quoted by Live Science on December 12.
“But in Bermuda, there is this other layer that is emplaced beneath the crust, within the tectonic plate that Bermuda sits on.”
Why Bermuda Is Different
The origin of this mysterious rock layer remains unclear, but scientists believe it could help explain one of Bermuda’s long-standing geological puzzles.
The archipelago sits atop an oceanic swell, meaning the seafloor beneath it rises roughly 500 meters higher than the surrounding ocean floor. Yet unlike other elevated regions, Bermuda shows no signs of active volcanism.
The islands’ last known volcanic eruption occurred around 31 million years ago, leaving researchers with a key question: what is still holding the seafloor up?
The newly identified rock layer may offer an answer. According to Frazer, the final eruption could have injected mantle material into the oceanic crust, where it cooled and solidified.
Over time, this dense slab may have acted like a buoyant raft, keeping the seafloor elevated long after volcanic activity ceased.
Not a Typical Hotspot
Most island chains, such as Hawaii, are formed by hotspots in the Earth’s mantle, where hot material rises and melts through the crust, creating volcanoes and causing the seafloor to bulge upward. As tectonic plates move away from these hotspots, the swell usually subsides.
Bermuda, however, does not follow this pattern.
“Bermuda's swell hasn't subsided, despite 31 million years of volcanic inactivity there,” Frazer said.
“There is some debate over what's happening in the mantle beneath the island, but there are no eruptions happening at the surface.”
Peering Beneath the Seafloor
To investigate what lies beneath Bermuda, Frazer and his colleague Jeffrey Park, a professor of Earth sciences at Yale University, analyzed seismic data recorded at monitoring stations on the islands.
They examined how seismic waves from major earthquakes around the world changed as they passed beneath Bermuda, allowing them to map structures up to 50 kilometers below the surface.
These changes revealed the presence of the unusually thick rock layer, which has a density distinct from both the overlying crust and the deeper mantle.
A Different Kind of Mystery
Bermuda is often associated with mystery because of the so-called Bermuda Triangle, where ships and aircraft have reportedly vanished. For scientists, however, the real enigma lies far below the ocean surface.
The findings were published in the journal Geophysical Research Letters on November 28 and may reshape scientists’ understanding of how ancient volcanic processes can leave lasting imprints deep within Earth’s crust.
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