Researchers at Arizona State University and the School of Earth and Space Exploration are investigating the “Large Low Shear Velocity Provinces” (or, for short, “LLSVPs”) – basically, two gigantic blobs located in the Earth’s mantle. Earth, one under Africa and one under the Pacific Ocean – to try and understand more about…well, what exactly they are.
These giant bubbles in our mantle live up to the adjective: both are about the size of an average continent and are about a thousand times higher than Mount Everest – aka “the tallest mountain on Earth”. Several studies have already been conducted on them, but few have yielded very conclusive information: we know that they are malleable and their shapes are unpredictable and complicated, but we do not know how they were created or reached their current form.
Theories on this are also several – a 2021 study, conducted by Qian Yuan of the university in Arizona, states that they may be remnants of the collision of “proto-Earth” against “Thea”, the space body that crashed into us and supposedly formed the moon.
Now, the same authors launch a new study, where they use geodynamic modeling based on previous research to create an analytical model of LLSVPs, obtaining more information through simulated observation.
The two researchers were able to uncover some additional information: the heights of both mantle bubbles depend on the viscosity of the material around them, as well as their respective densities. This is why, for example, the Africa bubble is about 1,000 km higher than its oceanic counterpart, but the Pacific bubble is more stable and older.
“Our calculations indicate that the initial volume of the bubbles does not affect their heights,” said Yuan. “African LLVP has had a more recent growth, within geologic time,” added Li. “This may explain the higher topography and intense volcanism in East Africa.”
In practical terms, because Africa’s bubble is younger and more unstable, it makes sense that the African terrain above it would suffer from more severe changes in topography. In other words: earthquakes, volcanism… all these geological activities can have an added impact on the region – the increase in size of the giant bubbles in the Earth’s mantle is also related to the movements of tectonic plates.
Not that things are any easier on its “sister”: the Pacific Ocean is surrounded by the so-called “Ring of Fire”, a horseshoe-shaped area that starts in the New Zealand region and goes all the way to the Peru-Chile submarine fault. Everything inside this “horseshoe” also has high geological activity – Tonga, where a recent explosion had a shock wave so powerful that its sound crossed the world twice, is in this area, for example.
We still don’t know the key details of the giant bubbles in Earth’s mantle, but the new study sheds more light on them. The material was published in Nature Geoscience.
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