Scientists have discovered why a small volcanic island in the middle of the Atlantic is still sitting high above the ocean floor, even though its volcanoes stopped erupting over 30 million years ago.
A team from the Carnegie Institution of Washington and Yale University revealed that a hidden structure under Bermuda formed after the area’s final volcanic eruption, which has secretly kept the island above the sea since prehistoric times.
Bermuda is a small group of islands in the North Atlantic Ocean, about 650 miles east of North Carolina, and is home to roughly 64,000 people.
The puzzle of why this vacation destination has remained high above the surrounding deep ocean floor has confused scientists for decades, especially since islands like this typically need regular infusions of volcanic heat to keep them afloat.
However, in Bermuda, the team discovered an extra, hidden slab of rock sitting directly beneath the island’s normal ocean crust.
This slab is about 12 miles thick and is lighter than the rock around it, so it floats like a giant raft and keeps the whole area lifted up.
Researchers believe this lighter layer formed 30 to 35 million years ago when hot, melted rock from deep inside Earth rose up, spread out underneath the crust and then cooled and hardened in place.
Unlike most raised ocean areas relying on active volcanoes to stay high above the waves, Bermuda’s swell has been credited to a previously unseen geological event, proving ancient volcanic leftovers can keep islands in place as well.
Pictured: Bermuda, a British island territory in the North Atlantic Ocean
Scientists have discovered a giant hidden structure which has kept Bermuda floating higher above the ocean
Researchers William Frazer and Jeffrey Park revealed that the hidden rock slab beneath Bermuda is enormous, measuring roughly 12 miles thick, which is about the same distance tip to tip as New York City’s Manhattan Island.
To figure this out without any new drilling, the scientists used more than 20 years of natural earthquake vibrations recorded by a single seismic listening station right on the island.
The scientists tracked how fast-moving earthquake pressure waves, which squeeze and stretch rock like sound waves, suddenly convert into slower side-to-side shaking ‘shear’ waves every time they hit a boundary between two different rock layers.
By processing hundreds of these earthquake signals with specialized tools and high-frequency filters, they precisely mapped the depths and thicknesses of every rock layer down to more than 25 miles below the island.
They also figured out why this rock is lighter than the surrounding mantle rock. It is composed of lightweight volcanic magma which is about 1.5 percent less dense, creating the exact amount of buoyancy needed to hold the Bermuda area 1,300 to 2,000 feet higher than the normal deep ocean floor.
This small density difference was calculated using simple floating physics that perfectly matched the observed height of the raised seafloor swell, proving the ancient cooled volcanic leftovers are still acting like a giant floatation device today.
Frazer said in a statement: ‘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.’
‘This suggests that there are other convective processes within Earth’s mantle that have yet to be well understood.’
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Does this discovery make the Bermuda Triangle feel less mysterious – or even stranger?
Researchers used decades of earthquake measurements to uncover the massive rock slab
Bermuda is home to several anomalies, including strange effects on magnetic signals and gravity
While scientists have never known about this hidden formation under Bermuda until the study in Geophysical Research Letters, the area has been tied to several strange features, some of which even distort the laws of gravity.
The Bermuda Rise is a giant underwater plateau stretching hundreds of miles across the sea floor that keeps the ocean bottom around Bermuda roughly 1,600 to 3,300 feet higher than the normal deep sea floor rocks of the same age.
This rise has mysteriously stayed elevated for millions of years even though there are no active volcanoes or hot spots pushing it up today.
The Bermuda Rise has been connected to several other strange abnormalities, including a gravitational anomaly where the pull of gravity is slightly weaker than expected because lighter rock hidden deep underneath makes the whole area more buoyant and ‘floaty.’
Due to this weaker area of gravity, the ocean surface actually sits slightly higher over the rise, creating a small bump in Earth’s natural sea level shape known as a geoid anomaly.
Another odd feature tied to the Bermuda Rise has been the high-amplitude magnetic anomalies.
These magnetic signals can make compasses and navigation equipment show bigger changes when planes or ships pass over the area, but they are completely natural and harmless.
Studies have shown that unusually strong signals produced by iron and titanium-rich rocks left over from Bermuda’s ancient volcanic past cause these changes.
