Bermuda is a fascinating island with a volcanic origin about 30-35 million years old. Unlike other volcanic islands, it doesn’t show the typical signs of volcanic activity. Recent research is reshaping the way we understand its unique structure.
Typically, hot mantle plumes create massive underwater volcanoes that eventually rise to form islands. As tectonic plates shift, these islands can erode while new ones form. However, Bermuda stands apart. It’s an archipelago of 181 islands, but it hasn’t experienced the volcanic activity that other islands, like Hawaii, have.
Seismic waves from earthquakes provide insight into Bermuda’s geology. These waves reveal two distinct layers in the Earth beneath Bermuda. When waves pass through different materials, their speed changes, similar to how light behaves when it passes through water or glass. This signals a change in density. Dr. William Frazer from the Carnegie Institution for Science and Yale’s Professor Jeffrey Park theorize that there’s a layer beneath Bermuda that’s about 50 kilograms per cubic meter lighter than surrounding areas, contributing to its unique support system.
This low-density layer, roughly 20 kilometers thick, acts like a mantle plume, keeping Bermuda afloat. Prior theories suggested Bermuda was supported by a weak thermal plume, but those have lacked strong supporting evidence. Interestingly, Bermuda hasn’t significantly subsided since its last volcanic activity, suggesting that whatever is supporting it is stable.
Data gathered from seismic waves during significant earthquakes across the Americas gives more evidence of this low-density layer. Frazer describes this phenomenon as unusual. In most regions, we expect to find a solid oceanic crust directly atop the mantle. But Bermuda features an additional layer within the tectonic plate, which helps the crust bend upwards.
The research also explains why Bermuda lacks the heat flow associated with active volcanic islands. This dense layer is believed to extend 50-100 kilometers outward, but it seems to be non-typical in shape.
This situation is somewhat similar to islands in French Polynesia, where underlying layers also provide support, albeit less dense and thinner. However, it’s still unclear how such a thick layer has formed only beneath Bermuda.
Interestingly, Bermuda’s volcanic rocks show unusually high carbon levels, which could relate to the Atlantic Ocean’s younger mantle source. Another theory suggests that internal forces in the mantle may fracture the crust, allowing seawater to react with it, producing unique geological features.
The ongoing study continues to shed light on the mysteries of Bermuda. It’s a reminder of how much there is still to learn about our planet.
For those interested in deepening their understanding, you can read more in the research published in Geophysical Research Letters.
