A new seismic analysis has revealed an unusually thick structure beneath Bermuda, a geological oddity that defies conventional models and may rewrite scientists’ understanding of how the island chain emerged.
The unusual feature consists of a 12.4-mile-thick layer of rock beneath the crust, located within the tectonic plate beneath Bermuda. Scientists have never detected such a thick layer of rock under similar tectonic conditions, where the mantle is typically found.
Bermuda Mystery
The 181-island chain of Bermuda has long puzzled geologists. The oceanic crust beneath the islands sits at a higher elevation than the surrounding seafloor due to a mysterious swell. Typically, volcanic activity would account for such uplift, yet geologists believe the region hasn’t experienced an eruption in 31 million years—a discrepancy that has fueled decades of speculation.
The newly discovered structure may help resolve that puzzle. Despite the extreme age of Bermuda’s last known eruption, the massive rock layer suggests that ancient volcanic activity could have injected a significant volume of mantle material into the crust. That slab now appears to be pushing the ocean floor upward by nearly 1,700 feet relative to nearby areas.
Similar mantle quirks may explain the formation of other islands worldwide. At certain locations known as mantle hotspots, rising plumes of hot material generate volcanic activity that builds islands from below—Hawaii being a prime example. In most cases, however, the crust eventually moves away from the hotspot, causing the uplift to subside over time.
Bermuda’s uplift, persisting for more than 31 million years, defies that pattern. What exactly is occurring beneath the island remains the subject of active debate.
Imagining the Bermuda Rock
The team behind the discovery, spread across multiple U.S. institutions, including Yale and Smith College, reported their findings in a new paper in Geophysical Research Letters. They relied on seismic data to make their discovery, drawing from a seismic station located on Bermuda, which collected the data by observing large earthquakes occurring at great distances from the island.
These observations allowed scientists to image the Earth below Bermuda to a depth of 31 miles. Changes in the signal received as the tremors reached Bermuda enabled the teams to identify the anomalous rock layer, which varied in density, thereby altering the seismic waves.
Earlier research on Bermuda’s geology revealed that the archipelago’s ancient lava was low in silica, indicating that it was produced from high-carbon rock. Further analysis of the material’s zinc content revealed that the lava originated deep in the mantle. Geologists believe that the rock originally entered the mantle during the formation of the Pangea supercontinent some 900 to 300 million years ago.
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