A bold claim: Bermuda hides a giant, unprecedented rock layer far deeper than any comparable formation on Earth. Forget the Bermuda Triangle for a moment—the newest Atlantic mystery lies beneath the archipelago, where scientists have identified a 12.4-mile-thick (about 20 kilometers) slab of rock beneath the oceanic crust that sits under Bermuda. This thickness is unlike anything seen in similar layers anywhere else on the planet.
Lead study author William Frazer, a seismologist at Carnegie Science in Washington, D.C., explains that, normally, one would expect to encounter the oceanic crust ending and then the mantle beginning. But Bermuda appears to host an additional layer that is pressed beneath the crust within the tectonic plate beneath the island.
Although the origin of this extra layer isn’t fully resolved, Frazer suggests it could illuminate Bermuda’s enduring enigmas. The island sits atop an oceanic swell—an elevated coastal region of the ocean floor—but unlike typical swell-forming hotspots associated with volcanism, Bermuda shows no signs of current volcanic activity. Its last known eruption dates back about 31 million years.
Bermuda’s reputation for mystery largely arises from the Bermuda Triangle, an area framed by Bermuda, Florida, and Puerto Rico where ships and aircraft have supposedly vanished at unusual rates. Yet, that feared proportion has often been exaggerated. The more compelling question is why Bermuda’s oceanic swell exists in the first place.
Many island chains, such as Hawaii, are believed to form above mantle hotspots—zones where hot material rises, fueling volcanic activity. When the crust moves over a hotspot, the seafloor can bulge upward; as tectonic plates drift away from the hotspot, the swell typically subsides. Bermuda, however, has not settled back down after tens of millions of years without any surface eruptions, leaving scientists debating what lies beneath.
To map the structure, Frazer and Yale University geosciences professor Jeffrey Park used recordings from a Bermuda seismic station that captured waves from distant large earthquakes. By analyzing how these seismic waves altered as they traveled through the Earth, they reconstructed images down to roughly 31 miles (50 kilometers) beneath Bermuda. The data revealed a notably thick, unusually low-density rock layer sandwiched beneath the crust.
The researchers published their results on November 28 in Geophysical Research Letters. As supporting voices enter the conversation, Sarah Mazza, a Smith College geologist not involved in the study, notes that remnants from Bermuda’s past volcanic activity could plausibly help maintain the island’s elevated topography. Her own work linking low-silica lava types to carbon-rich rocks, and zinc-isotope studies pointing to a deep-m mantle origin for Bermuda’s carbon, reinforce the idea that the Atlantic’s relative youth and the continent’s ancient history may shape why Bermuda is so distinctive.
According to Mazza, Bermuda’s carbon likely originated deep in the mantle during the era when the supercontinent Pangea formed between about 900 and 300 million years ago—a different pattern from hotspot volcanism seen in the Pacific or Indian oceans. The Atlantic’s relative youth, born from Pangea’s breakup, may explain why Bermuda’s situation diverges from those other regions.
Frazer is now broadening the search to other islands around the world to determine whether Bermuda’s thick layer is a local oddity or a rare example of a broader geologic process. He argues that studying such extreme places helps reveal the normal mechanisms at work across Earth and clarifies what makes some regions unusually dynamic.
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