Giant Rock Mass Under Bermuda Reveals Island’s Ancient Origins
A massive, buried layer of rock approximately 20 kilometers (12.4 miles) thick has been discovered beneath Bermuda, offering a potential explanation for how the archipelago has remained above sea level for over 30 million years after volcanic activity ceased. The discovery challenges conventional geological understanding of oceanic island formation, and longevity.
Unusual Subsurface Structure
Seismologist William Frazer of the Carnegie Institution for Science analyzed seismic wave patterns passing beneath the islands and identified an anomalous boundary where the mantle typically begins. This unexpected layer is roughly twice as thick as similar structures found under most oceanic islands and exhibits a slightly lower density than the surrounding mantle material. This density difference creates a buoyant effect, preventing the islands from gradually sinking into the ocean.
“Typically, you have the bottom of the oceanic crust, and then it would be expected to be the mantle,” explained Dr. Frazer in an interview with The Royal Gazette. “But in Bermuda, there is this other layer that is emplaced beneath the crust, within the tectonic plate that Bermuda sits on.”
Magma’s Ancient Journey
Researchers believe the layer formed from magma that didn’t erupt to the surface. Instead, it spread beneath the oceanic crust and solidified over time. Chemical analysis of ancient Bermuda lavas revealed unusually low silica content and the presence of carbon-rich materials, suggesting the melt originated from reworked rocks deep within the Earth’s mantle. ScienceAlert reports on this finding.
A Unique Geological History
Unlike volcanic island chains like Hawaii, which are formed by a moving tectonic plate over a stationary hotspot and exhibit a progression of volcanoes of varying ages, Bermuda doesn’t follow this pattern. It lacks a long chain of volcanoes and isn’t associated with an active thermal plume. This suggests the islands’ elevated position isn’t due to current mantle heating processes but rather to ancient geological events.
William Frazer, the lead author of the study, is a geophysicist specializing in imaging the Earth’s crust and mantle. He is currently a postdoctoral fellow at the Carnegie Institution for Science. More information about Dr. Frazer’s research can be found on the Carnegie Science website.
Future Research
The extent to which this hidden layer is unique to Bermuda remains unknown. Further research is needed to determine if similar structures exist beneath other oceanic islands. This discovery prompts a re-evaluation of the mechanisms that contribute to the long-term survival of islands in the open ocean.