The Bermuda Triangle has been the source of tall tales for decades, but deep in the North Atlantic Ocean lies a real mystery that has always left geologists perplexed. The Bermuda archipelago sits on a piece of oceanic crust that swells and rises above the surrounding crust. This wave itself is not that unusual, as its feature often results from ongoing volcanic activity in other parts of the world. The catch is that Bermuda has not been volcanically active for the last 30 to 35 million years.
New research published in Letters on Geophysical Research The cause of the mysterious underwater wave may have just been revealed. During the study, scientists examined seismic data and found that beneath the oceanic crust lies a layer of rock approximately 12 miles (20 kilometers) thick. This layer may have been there since Bermuda's last eruption, but shockingly, the wave beneath the island has not disappeared in all these years.
Read more: Fat molecules in deep-sea mud volcanoes reveal how microbes survive extreme conditions
Birth of volcanic islands
One way volcanic islands arise is when mantle plumes resulting from a breakthrough of the boundary between the Earth's core and mantle through the oceanic crust. Magma rising from the depths of the Earth forms plumes, columns of molten floating rock that subsequently serve as the basis for seamounts (seamounts) and volcanic island chains.
For example, Hawaii and the Galapagos Islands are volcanic island chains formed by volcanic hotspot activity; in this process, tectonic plate It glides over a stationary “hot spot” in the mantle, releasing magma from the ocean floor, building island after island like a volcanic conveyor belt, according to the British Geological Survey.
Material from mantle plumes also causes parts of the oceanic crust to swell, although this feature usually disappears as the tectonic plate moves the crust.
Bermuda sits at the top of a wave, but unlike Hawaii or the Galapagos Islands, it is not volcanically active and does not have a mantle plume. This presented a mystery to geologists, who tried to theorize how the wave maintained its shape without active volcanism.
Solving the mystery of the swell
In a new study, scientists solved this mystery by examining seismic data from distant earthquakes recorded at a seismic station in Bermuda. By seeing how differently earthquake waves behave beneath the island, they were able to find evidence of a thick layer of rock beneath the oceanic crust that is less dense than the surrounding mantle material.
According to the researchers, this layer of rock may be a remnant of volcanic activity that occurred during the creation of the island. This layer is estimated to be approximately 12 miles (20 km) thick and twice as thick as other instances of subplating, which occurs in areas where mantle material becomes trapped within the crust or beneath the Moho (the boundary between the crust and the mantle).
Because this layer is less dense than the rest of the mantle, it imparts buoyancy to the swell, allowing it to maintain its shape in the absence of heat or volcanic activity. The researchers also say the layer likely extends like the underlying slab beneath the Hawaiian Islands.
“In the case of Bermuda, the lower plate may extend beyond the volcanic edifice and be bowl-shaped. If the lower plate extends beyond the edifice, we estimate it to be ~200 km. [124 miles] be the extreme upper limit of the lateral extent of the undercover and consider the possibility of undercover over a distance of 50 to 100 km. [31 to 32 miles] from the island to be more intelligent,” the researchers wrote in the study.
Sea level rise in Bermuda
While Bermuda, made up of 181 islands, doesn't have to worry about active volcanoes, its residents have to deal with the growing effects of climate change.
According to the National Oceanic and Atmospheric Administration, the relative sea level trend for Bermuda is 2.18 millimeters per year, based on monthly average sea level data from 1932 to 2024. This is equivalent to a change of 0.72 feet per 100 years. While that may not seem like much, such a small change could still pose a threat to Bermuda, where more than 20 percent of the land is below 6.5 feet, according to the Bermuda Institute of Ocean Sciences and Arizona State University.
Read more: What is the scientific mystery of the Bermuda Triangle?
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