Beneath the well-known enigmatic archipelago lies a new puzzle of the North Atlantic. Scientists have detected a strange 20-kilometer-thick layer of rock beneath the oceanic crust near the Bermuda Islands. Such thickness has never been observed in any other similar stratum globally.
“Typically, beneath the oceanic crust is its lower part, and then the mantle is expected,” said lead researcher William Fraser of the Carnegie Institution in Washington. “But at the Bermuda Islands, there is another layer situated under the crust, within the tectonic plate holding Bermuda.”
Although the origin of this layer is not entirely clear, it might account for one of the unsolved mysteries of the Bermudas, Fraser noted. The island sits on an oceanic rise where the oceanic crust is higher than the surrounding rocks. Yet, there is no evidence of any ongoing volcanic activity that formed this elevation—the last known eruption there occurred 31 million years ago.
The discovery of this new massive “structure” suggests that the final eruption might have injected mantle rock into the Earth’s crust, where it solidified in place, forming something akin to a raft that lifted the seafloor by about 500 meters.
The Bermuda Islands have long held a reputation as a mysterious location, mainly due to the Bermuda Triangle—the region between the archipelago, Florida, and Puerto Rico, where, reportedly, an unusually high number of ships and planes have vanished. (However, this fame is largely exaggerated.) The true enigma, nevertheless, is why such a significant oceanic uplift exists at Bermuda.
Island chains like Hawaii are thought to exist because of mantle hotspots—places in the mantle where hot material rises, causing volcanic action. Where the hotspot meets the crust, the seafloor often rises. But as tectonic motion shifts the crust away from that hotspot, the oceanic uplift usually subsides.
Fraser stated that despite 31 million years without volcanic activity at the Bermudas, the rising has not receded. There is debate about what is happening in the mantle beneath the island, but no eruptions are occurring at the surface.
Fraser and co-author Professor Jeffrey Park utilized seismic station records from Bermuda, capturing major earthquakes in various parts of the world, to gain insight into the Earth up to 50 km deep below the islands. They examined locations where seismic waves from these tremors abruptly changed. This technique allowed them to identify the unusually thick layer of rock, which has a lower density than the adjacent rocks.
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