Geophysical Study Confirms 20-Kilometer Rock Layer Supporting Bermuda's Elevation

A scientific investigation concluded in late 2025 has confirmed the existence of a substantial geological formation beneath the Bermuda Islands, providing a definitive geophysical explanation for the archipelago's sustained elevation. The discovery challenges conventional models regarding the support structures of oceanic crust.

The core finding identifies an anomalous layer of rock, approximately 20 kilometers thick, situated between the oceanic crust and the Earth's mantle directly beneath Bermuda. Researchers, led by principal author William Frazer of Carnegie Science in Washington D.C., and co-author Jeffrey Park of Yale University, mapped this subsurface structure using seismic wave analysis derived from numerous large global earthquakes. By tracking abrupt changes in the speed and direction of these seismic waves as they passed through the region down to approximately 50 kilometers, the team developed a detailed vertical profile of the area.

This analysis revealed the extra layer, which possesses a lower density than the surrounding mantle material, effectively acting as a buoyant geological foundation. Calculations indicate this layer provides the necessary lift, elevating the seafloor by about 500 meters above the adjacent abyssal plain, a feature known as the Bermuda oceanic swell. This sustained elevation is unusual because most volcanic islands, such as those in the Hawaiian chain, typically subside once tectonic movement carries them away from their underlying mantle hotspot. Bermuda has remained elevated despite its last known volcanic activity occurring approximately 31 million years ago.

The research team hypothesizes that during the final stage of volcanism, molten material from the mantle intruded beneath the crust and solidified in place, creating this thick underplated layer. This mechanism accounts for the lack of significant subsidence over geological timescales, differentiating Bermuda from standard hotspot-formed islands. The findings were formally published in the journal Geophysical Research Letters on November 28.

Geologist Sara Mazza of Smith College, who provided external context regarding the island's distinct chemistry, suggests that Bermuda's position at the former core of the ancient supercontinent Pangea may be relevant to this phenomenon. Mazza's prior work indicated that Bermuda's lavas are low in silica and high in carbon, suggesting the material originated from deep within the mantle, possibly during the breakup of Pangea between 900 million and 300 million years ago. This historical context implies the Atlantic basin may have inherited a unique mantle composition.

William Frazer stated that the subsequent phase of the investigation will involve expanding the seismic analysis to other global islands to determine if this 20-kilometer structure is unique or representative of a broader, currently unrecognized, geological process. Understanding this extreme location, Frazer noted, is essential for differentiating between standard Earth processes and more exceptional geological occurrences. The discovery necessitates a re-evaluation of geophysical models concerning the long-term support and evolution of oceanic island structures.