A new scientific study helps explain why Bermuda remains elevated in the Atlantic Ocean even after more than 30 million years of volcanic inactivity. Unlike what happens on other volcanic origin islands, which tend to sink gradually after the crust cools, Bermuda appears to have been “sustained” by an unusual geological structure located below its oceanic crust.
The research was published in the scientific journal Geophysical Research Letters and conducted by a team led by seismologist William Frazer from the Carnegie Science institute, in partnership with geophysicist Jeffrey Park from Yale University. The results were also detailed in interviews given to specialized outlets like Live Science.
Normally, when a volcano goes extinct, the tectonic plate moves away from the deep mantle hotspot that fed it. Over time, the crust and the volcano itself cool, become denser, and sink slowly. In Bermuda, however, this process did not occur as expected.
By analyzing seismic waves generated by 396 distant earthquakes — all strong enough to cross large portions of the planet — the researchers managed to map a vertical image of the rocks under Bermuda, reaching about 31 miles (approximately 50 kilometers) deep. What they found was a layer of rock about 20 kilometers thick, a type of structure never before observed in any other region of the world.
This layer, less dense than the surrounding rocks, is positioned right below the oceanic crust, within the tectonic plate itself. According to Frazer, this completely deviates from the expected pattern. “But in Bermuda, there is this other layer positioned under the crust, within the tectonic plate on which Bermuda sits,” he told the specialized magazine Live Science.
Bermuda is located on an oceanic elevation, where the seabed is about 500 meters higher than neighboring areas. Scientists believe the last phase of volcanic activity may have forced mantle material into the crust, where it cooled and became trapped, forming a geological “raft”-like structure that supports the island above the ocean floor.
The exact origin of this layer is still a matter of debate. In an interview with the Brighter Side of News website, Jeffrey Park stated that “part of the magma may have been retained under the surface instead of erupting, forming a mafic pluton over time.” He added that “volatile-rich melts ascending under Bermuda could also have efficiently depleted and modified the uppermost mantle, leaving behind a lighter residue.”
Another hypothesis raised by the researchers is so-called sub-plate metasomatism. In this scenario, ascending hot material would have fractured the crust, allowing seawater to enter and causing partial serpentinization of the mantle, which would also reduce its density.
Although volcanism in Bermuda has been extinct for about 31 million years, there are no signs of new surface eruptions. Still, the remaining geological structure continues to exert direct influence on the island’s stability. For geologist Sarah Mazza from Smith College, who did not participate in the study, this legacy is fundamental to understanding the phenomenon. “There is still this remnant material from the days of active volcanism under Bermuda that is potentially helping to sustain it as this high-relief area in the Atlantic Ocean,” she told Live Science. She also highlighted the region’s unique geological context: “The fact that we are in an area that was previously the heart of the last supercontinent is, I believe, part of the story of why this is unique.”
Now, William Frazer plans to expand the research to other islands around the world, seeking similar formations. The goal is to discover whether the structure found under Bermuda is truly unique or if it may exist in other points on the planet. “Understanding a place like Bermuda, which is an extreme location, is important for understanding less extreme places and gives us an idea of what the more normal processes that happen on Earth are and what the more extreme processes that happen are,” the researcher stated.
Source: brasil247.com