For decades, geologists have struggled to explain one of the Atlantic Ocean’s biggest geological mysteries: why does Bermuda remain elevated far above the surrounding seafloor despite its volcanoes becoming inactive more than 30 million years ago?
Now, a team of American researchers believes it has finally uncovered the answer hidden deep beneath the island.
The new study, led by seismologist William Frazer and Jeffrey Park, suggests Bermuda is supported by a unique underground geological structure unlike anything previously observed on Earth.
Why Bermuda Has Long Confused Scientists
Most volcanic island chains, including Hawaii, are formed above mantle plumes — columns of extremely hot rock rising from deep inside Earth’s mantle.
As the hot material rises, it pushes the seafloor upward and creates volcanoes. Over millions of years, tectonic plates shift away from the plume, volcanic activity fades, and the elevated seafloor slowly sinks back down.
But Bermuda never fully sank.
The island still sits atop a massive underwater swell roughly 1,600 feet higher than the surrounding Atlantic Ocean floor, something that conventional mantle plume theories could not fully explain.
Scientists Used Earthquake Waves To Look Beneath Bermuda
To investigate the mystery, the researchers analysed seismic waves generated by powerful earthquakes worldwide.
As these waves move through Earth, they travel at different speeds depending on the density and composition of the material underground. By studying recordings collected from a seismic station on Bermuda, the team created a detailed picture of Earth’s interior beneath the island down to nearly 20 miles deep.
What they discovered surprised them.
Massive “Underplating” Layer Found Beneath Island
The researchers identified a layer of rock more than 12 miles thick located beneath Bermuda’s oceanic crust.
Unlike the dense mantle surrounding it, this rock is unusually light and buoyant. Instead of a mantle plume actively pushing upward, the underground layer appears to function like a giant geological raft that helps keep Bermuda and the surrounding seafloor elevated.
Scientists believe this structure, known as an “underplating,” formed millions of years ago during Bermuda’s volcanic past. At the time, carbon-rich molten rock intruded into the base of the crust and later cooled into place.
Researchers think this material may have originated deep within Earth during the formation of the ancient supercontinent Pangaea hundreds of millions of years ago.
Researchers Say Bermuda May Represent Unknown Mantle Processes
Explaining the findings, Frazer said Bermuda does not fit the traditional mantle plume model seen in places like Hawaii.
“Bermuda is an exciting place to study because a variety of its geologic features do not fit the model of a mantle plume, the classic way for deep material to be brought to the surface,” he said.
He added that the discovery suggests there may be other poorly understood convective processes occurring deep inside Earth’s mantle.
The team is now investigating whether similar underground structures exist beneath other islands worldwide. If found elsewhere, Bermuda may not be unique but instead the first known example of a much broader geological phenomenon.