Bermuda has always been a bit of a riddle for everyone: geologists as well as the common man. The island’s volcanoes are expected to be long dead, quiet for over 30 million years now, yet Bermuda still perches high above the surrounding Atlantic seafloor, and that never made much sense.
So, what’s keeping it up there?
Turns out, a group of researchers from the U.S. think that they have finally got a solid answer, and it is buried deep under the island. William Frazer and Jeffrey Park led the new study, and their work just appeared in Geophysical Research Letters.
Bermuda does not behave like other volcanic islands
Normally, the volcanic islands form when mantle plumes (think of columns of super-hot rock) blast their way upward from deep within the planet. These plumes burst through the crust, erupt to create islands, and raise the ocean floor along the way. But after the volcanic fireworks are over, the uplift usually relaxes; the islands settle and sink over time. That’s what happened in Hawaii. Not Bermuda.
Right now, even though Bermuda’s volcanism ceased millions of years ago, the island still stands out, about 1,600 feet higher than the ocean floor nearby. That’s strange.
Researchers used earthquake waves to study underground structure
To get some answers, the team turned to seismic waves: the vibrations that earthquakes send rippling through the Earth. By tracking how those waves speed up or slow down as they hit different rocks, the scientists used a seismic station on Bermuda to ‘see’ nearly 20 miles below the ground. What they spotted was a shock.
Massive buoyant rock layer found beneath Bermuda
Underneath the island, they found a massive slab of rock, over 12 miles thick, that was sandwiched beneath Bermuda’s oceanic crust. This is not your usual dense mantle rock, it is lighter and more buoyant. So instead of relying on a hot plume below, Bermuda actually sits on what’s basically a huge, floating raft. This process is called "underplating".
Here’s how it probably happened:
Ages ago, molten rock loaded with carbon seeped into the lower crust and cooled into a lighter layer, permanently parked under Bermuda.
Possible connection to ancient supercontinent Pangea
The odd material could trace its roots way back, to when the supercontinent Pangea was coming together, hundreds of millions of years ago. That matters because it hints at some inner-Earth processes nobody’s really understood earlier.
Frazer puts it bluntly: Bermuda just does not fit the usual textbook plume island story.
Discovery could change understanding of Earth’s interior
Now, scientists are asking if the islands around the world have the same underground surprise or not. If they do, then this discovery could turn a lot of assumptions about Earth’s mantle, volcanic islands, and how material moves inside our planet on its head.
