Scientists say the real mystery surrounding Bermuda is buried deep beneath the ocean floor.
Researchers have discovered an unusually thick layer of rock — about 20 kilometers (12.4 miles) — sitting below the oceanic crust under Bermuda, something that has never been observed anywhere else in the world.
“Normally, you have the oceanic crust, and right beneath it is the mantle,” said William Frazer, a seismologist at Carnegie Science and lead author of the study. “But beneath Bermuda, there’s an extra layer that shouldn’t really be there.”
Bermuda: A Geological Puzzle
The discovery may help explain a long-standing geological puzzle: why Bermuda sits on an “oceanic swell,” or a raised section of the seafloor, despite having no active volcano. The island’s last known eruption happened around 31 million years ago.
Scientists believe that during that ancient volcanic phase, molten mantle rock may have intruded into the crust and cooled there, forming a dense but buoyant slab. This buried “raft” could still be propping up the seafloor today, lifting it by about 500 meters (1,640 feet).
Bermuda is often linked to mystery because of the Bermuda Triangle — a region between Bermuda, Florida, and Puerto Rico associated with exaggerated claims of missing ships and planes. But geologists say the real question is why Bermuda’s oceanic swell never subsided.
In island chains like Hawaii, mantle hotspots push magma upward, creating volcanoes and raising the crust. Once tectonic plates move away from the hotspot, the swell typically sinks. Bermuda, however, has remained elevated for tens of millions of years without any surface eruptions.
Low-Density Rock
To look beneath the island, Frazer and co-author Jeffrey Park of Yale University analyzed seismic waves from large earthquakes around the world, recorded by a seismic station in Bermuda.
Changes in how the waves traveled revealed the presence of the thick, low-density rock layer beneath the crust.
The findings were published on November 28 in the journal Geophysical Research Letters.
“There’s still leftover material from Bermuda’s volcanic past that may be helping keep this area elevated,” said Sarah Mazza, a geologist at Smith College who was not involved in the study.
Mazza’s own research suggests Bermuda’s lava came from carbon-rich material deep in the mantle, possibly dating back to the formation of the supercontinent Pangea hundreds of millions of years ago. This could explain why Bermuda is different from volcanic islands in the Pacific and Indian oceans.
“The Atlantic is a relatively young ocean,” Mazza said. “And the fact that this area used to be the heart of a supercontinent may be key to why Bermuda is so unique.”
Frazer said he is now studying other islands to find out whether similar hidden layers exist elsewhere — or if Bermuda truly stands alone.
“Understanding extreme places like Bermuda helps us better understand how Earth usually works,” he said, “and when it behaves in unexpected ways.”
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