For decades, scientists have been puzzled by one strange question about Bermuda: why does the island still sit unusually high above the Atlantic Ocean floor even though its volcanoes died out more than 30 million years ago?
Now, researchers from Carnegie Institution for Science and Yale University believe they may finally have the answer, and it appears to be hiding deep beneath the island itself.
Their findings, published in Geophysical Research Letters, suggest Bermuda is being supported by a rare underground geological structure unlike anything clearly observed elsewhere on Earth.
Why Bermuda Has Confused Scientists For So Long
Normally, volcanic islands such as Hawaii form above what geologists call a mantle plume, a massive column of hot rock rising from deep inside Earth’s mantle.
As the plume pushes upwards, it creates volcanoes and lifts the seafloor around it into a broad swell.
But over millions of years, once volcanic activity stops and tectonic plates shift away, those swells usually begin sinking back down.
That’s where Bermuda became a scientific headache.
Despite its volcanoes being inactive for tens of millions of years, Bermuda still sits roughly 1,600 feet above the surrounding ocean floor, according to Carnegie Science.
And until now, nobody fully understood why.
Scientists Used Earthquake Waves To Look Beneath Bermuda
The new study was led by seismologist William Frazer from Carnegie Science and geophysicist Jeffrey Park from Yale University.
To investigate the mystery, the researchers analysed seismic waves generated by large earthquakes around the world.
As these waves travel through Earth, they move differently depending on the density and composition of underground rock layers. By studying recordings collected from a seismic station in Bermuda, the team managed to build an image of Earth’s interior beneath the island down to around 20 miles deep.
What they discovered surprised them.
A Giant ‘Floating Raft’ Of Rock May Be Holding Bermuda Up
According to the study, researchers identified a massive layer of unusually light rock buried beneath Bermuda’s oceanic crust.
The layer measures more than 12 miles thick and appears less dense than the surrounding mantle rock, making it naturally buoyant.
Instead of Bermuda being held up by an active mantle plume underneath, scientists now believe this lighter rock behaves more like a giant underground raft that helps keep the island elevated.
The process is known as “underplating”.
Researchers think it formed during Bermuda’s volcanic past, when carbon-rich molten rock from deep within Earth forced its way into the base of the crust and eventually cooled there permanently.
Interestingly, the material may trace its origins back hundreds of millions of years to the formation of Pangaea, the ancient supercontinent that existed long before today’s continents separated.
Scientists Say Bermuda Doesn’t Fit Traditional Geological Models
Frazer said Bermuda is particularly fascinating because many of its geological features don’t match the standard mantle plume theory used to explain most volcanic islands.
“Bermuda is an exciting place to study because a variety of its geologic features do not fit the model of a mantle plume,” Frazer explained, according to Carnegie Science.
“We observe thick underplating, something that is not observed at most mantle plumes.”
He added that the findings suggest scientists may still not fully understand all the convective processes happening deep within Earth’s mantle.
“This suggests that there are other convective processes within Earth’s mantle that have yet to be well understood,” Frazer said.
Following the discovery, Frazer is now investigating whether similar hidden structures may exist beneath other islands around the world.
If confirmed elsewhere, Bermuda may not be a one-off geological oddity after all, it could simply be the first identified example of a much broader phenomenon hidden deep beneath Earth’s oceans.
For now though, the mysterious Atlantic island has once again reminded scientists that Earth still holds plenty of secrets beneath its surface.
