Long Valley supervolcano: Geologists wonder if it's 'waking up'
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Researchers have uncovered new details about the two mysterious blob-like structures, present roughly on opposite sides of the planet. Officially known as Large Low-Shear-Velocity Provinces (LLSVPs), these blobs are massive, each the size of a continent and 100 times taller than Mount Everest. Until now, scientists have known very little about these blobs, about why they exist, and why they have odd shapes of varying heights.
Now, researchers have analysed the structures and were able to determine the maximum heights that the blobs reach, along with how the volume and density of the blobs, as well as the viscosity in the surrounding mantle, may influence their height.
Arizona State University scientists Qian Yuan and Mingming Li of the School of Earth and Space Exploration used geodynamic modelling and analysis to learn more about the two blobs.
The results of their seismic analysis led to a surprising discovery that the blob under the African continent is about 621 miles (1,000 km) higher than the blob under the Pacific Ocean.
According to Mr Yuan and Mr Li, the best explanation for the vast height difference between the two is that the blob under the African continent is less dense (and therefore less stable) than the one under the Pacific Ocean.
Mr Yuan, the lead author said: “Our calculations found that the initial volume of the blobs does not affect their height.
“The height of the blobs is mostly controlled by how dense they are and the viscosity of the surrounding mantle.”
To conduct their research, the two scientists designed and ran hundreds of mantle convection models simulations.
They exhaustively tested the effects of key factors that may affect the height of the blobs, including the volume of the blobs and the contrasts of density and viscosity of the blobs compared with their surroundings.
They found that, to explain the large differences of height between the two blobs, the one under the African continent must be of a lower density than that of the blob under the Pacific Ocean, indicating the two may have different compositions and evolution.
Co author Mr Li added: “The Africa LLVP may have been rising in recent geological time.
“This may explain the elevating surface topography and intense volcanism in eastern Africa.”
These findings may fundamentally change the way scientists think about the deep mantle processes and how they can affect the surface of the Earth.
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The unstable nature of the blob under the African continent, for example, may be related to continental changes in topography, gravity, surface volcanism and plate motion.
Mr Yuan said: “Our combination of the analysis of seismic results and the geodynamic modelling provides new insights on the nature of the Earth’s largest structures in the deep interior and their interaction with the surrounding mantle.
“This work has far-reaching implications for scientists trying to understand the present-day status and the evolution of the deep mantle structure, and the nature of mantle convection.”
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