For decades, geologists have remained puzzled by one of the Atlantic Ocean’s most enduring mysteries: why Bermuda sits unusually high above the surrounding ocean floor despite its volcanoes having remained inactive for more than 30 million years. Now, a team of American scientists believes it has uncovered the explanation hidden deep beneath the island.
New research led by William Frazer of Carnegie Science and Jeffrey Park of Yale University suggests that Bermuda is supported by a rare geological structure unlike anything previously identified elsewhere on Earth.
Scientists explained that most volcanic island chains, including Hawaii, are formed above mantle plumes — columns of hot rock rising from deep within Earth’s mantle. These plumes create volcanoes and raise the seafloor. Over millions of years, as tectonic plates move away and volcanic activity ends, the elevated regions generally sink back toward the ocean floor. However, Bermuda has remained elevated, standing roughly 1,600 feet above the surrounding seabed.
To investigate the anomaly, the researchers analysed seismic waves generated by major earthquakes around the world. Using recordings from a seismic station in Bermuda, they mapped Earth’s interior to a depth of nearly 20 miles beneath the island.
Their findings revealed an unexpected layer of rock more than 12 miles thick beneath the oceanic crust. The rock was found to be less dense than the surrounding mantle, making it unusually buoyant. Rather than being pushed upward by an active mantle plume, scientists believe this lighter rock acts like a raft that keeps Bermuda and the surrounding seafloor elevated.
Researchers said the geological layer, known as an underplating, likely formed during Bermuda’s volcanic past when carbon-rich molten mantle rock entered the base of the crust and cooled over time.
Frazer said, “Bermuda is an exciting place to study because a variety of its geologic features do not fit the model of a mantle plume, the classic way for deep material to be brought to the surface.”
He added, “We observe thick underplating, something that is not observed at most mantle plumes. Combined with recent geochemical observations, this suggests that there are other convective processes within Earth’s mantle that have yet to be well understood.”
