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Scientists are not sure how or why this giant rock formation formed, but it may be related to volcanic activity in the area that ceased about 31 million years ago. . |Photo source: mtcurado/Getty Images
Step aside, Bermuda Triangle: the North Atlantic’s latest mystery lies beneath this mysterious archipelago. Scientists have discovered a strange, 12.4-mile-thick (20 kilometers) rock formation beneath Bermuda’s ocean crust. This level of thickness has never been seen in any other similar layer worldwide.
“Typically, you have the bottom of the oceanic crust, and then that would be the mantle,” said the study’s lead author. william fraser“But in Bermuda, there’s another layer beneath the crust within the tectonic plate that Bermuda sits on,” said Seismologist at the Carnegie Science Center in Washington.
Fraser told LiveScience that while the origin of this layer is not entirely clear, it may explain an ongoing mystery in Bermuda. The island sits on the waves, where the oceanic crust rises above its surroundings. But there’s no evidence that any ongoing volcanic activity is responsible for the swelling – the island’s last known volcanic eruption was 31 million years ago.
The discovery of the new giant “structure” suggests that the last eruption may have injected mantle rocks into the crust, where they froze and formed raft-like objects that raised the seafloor by about 1,640 feet (500 meters).
Bermuda has long had a reputation for mystery, largely due to the Bermuda Triangle, an area between Bermuda, Florida and Puerto Rico where an unusual number of ships and planes are said to have gone missing. (However, this reputation has been largely exaggerated.) The real mystery, however, is why Bermuda Ocean swells exist.
Island chains like Hawaii are thought to exist due to mantle hotspots, which are places in the Earth’s mantle where hot material rises and creates volcanic activity. Where hot spots meet the crust, the seafloor often rises. But when tectonic movements slide the Earth’s crust away from this hot spot, the ocean expansion usually recedes.
Fraser said that even though Bermuda’s volcano has been inactive for 31 million years, its expansion has not subsided. There is some debate about what is happening in the mantle beneath the island, but no volcanic eruptions occur on the surface.
Fraser and study co-authors Jeffrey ParkerThe Yale University professor of earth and planetary sciences used the Bermuda Seismological Observatory’s records of distant large earthquakes around the world to obtain an image of the Earth about 31 miles (50 kilometers) below Bermuda. They examined where the seismic waves of these earthquakes changed suddenly. This revealed an unusually thick layer of rock that is less dense than other surrounding rocks.
Their findings are published in the Nov. 28 issue of the journal Geophysical Research Letters.
“Material left over from active volcanic activity still exists beneath Bermuda and may help identify Bermuda as a high-relief area of the Atlantic Ocean.” Sarah MazzaA geologist at Smith College in Massachusetts who was not involved in the work told Live Science.
Mazza’s own research into Bermuda’s volcanic history found that the lava minerals there were low in silica, suggesting they came from high-carbon rocks. Mazza’s examination of molecular changes in zinc in Bermuda samples was published in the journal in September geologyfound that this carbon comes from deep within the Earth’s mantle. It was likely first pushed there when the supercontinent Pangea formed 900 million to 300 million years ago, Mazza said. This is different from what is seen on islands formed by hotspots in the Pacific or Indian Ocean, she added. This difference may be because the Atlantic Ocean that opened when Pangea broke up was a young ocean compared to the Pacific or Indian Oceans at the edge of Pangea.
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“I think the fact that our region was once the center of the last supercontinent is part of its uniqueness,” she said.
Fraser is now examining other islands around the world to determine if there are similar formations to those found under Bermuda, or if the archipelago is indeed unique.
“Understanding an extreme place like Bermuda is important for understanding less extreme places, and it gives us an idea of what are the more normal processes that are happening on Earth and what are the more extreme processes that are happening on Earth,” Fraser said.
