Enormous Blob Deep Beneath Africa Is Slowly Rising, Scientists Discover

Deep beneath Earth's surface, on opposite sides of the planet, sit two enormous blob-like structures spanning thousands of miles. And one of them, beneath Africa, is slowly creeping up towards the surface.

Scientists first spotted the two giant structures via seismic observations. These anomalies sit in the lowermost mantle, between around 400 and 1,600 miles below Earth's surface, above the outer core.

One blob is beneath the Pacific Ocean, while the other is under Africa. They are known as Low-Shear-Velocity Provinces (LLSVPs) and are known to influence processes at the core as well as the mantle. The blobs are thought to be incredibly dense "thermochemical piles" composed of recycled oceanic crust or iron-rich material.

Researchers from Arizona State University have studied these blobs to better understand what they are and where they sit in Earth's mantle, with the findings published in Nature Geoscience.

Qian Yuan and Mingming Li performed seismic analysis, running hundreds of mantle convection simulations. Results showed that the two blobs differ in terms of density, with the African LLSVP appearing to be far less dense, and as a result, less stable, than its Pacific counterpart.

The blob under Africa sits about 620 miles higher than the Pacific LLSVP. The African blob has a maximum height of about 990 to 1,100 miles, while the Pacific anomaly is between 430 and 500 miles high.

The difference in height and density, they said, indicates the anomalies have "different compositions, dynamics and evolution histories."

earth core
Two enormous "blobs" sit deep beneath the surface of Earth, just above the boundary to the upper core. Getty Images

Yuan told Newsweek: "We had a sense that the African LLVP is higher than the Pacific, but we were really surprised when we found the African one is much higher ... than the Pacific."

LLSVPs have previously been linked to volcanism. They appear to be able to generate plumes to Earth's surface at their edges, deflecting mantle flow upwards. A study published in 2020 linked this blob to volcanic activity in southeastern Africa between 155 and 95 million years ago.

"The Africa LLSVP may have been rising in recent geological time," Li said in a statement "This may explain the elevating surface topography and intense volcanism in eastern Africa."

Yuan told Newsweek: "African LLVP is relatively lighter, so it has the ability to keep moving up, while we have not calculated the speed of its rising and we are also not sure if it already reached the surface in the past, but if it keeps rising, it may still need a few million years to reach the surface."

She said that if the blob is still rising, it may result in more supervolcanoes and earthquakes in Africa millions of years from now.

Li told Newsweek the blob is probably rising at a rate of around one to two centimeters per year. "The top of the African LLVP is at a depth of [around] 1,000 km. Therefore, it would take about 50-100 millions of years for it to reach the surface, assuming it raises with a velocity of 1-2 cm per year. In fact, as the African rises, it may become cold and dense. It is not impossible for it to sink again when it becomes dense enough."

Yuan and Li said the findings may influence how scientists study LLSVPs and how they influence activity on Earth's surface. As well as volcanic activity, the blobs have been linked to topographic changes, magnetic fields and the motion of the tectonic plates.

"Our combination of the analysis of seismic results and the geodynamic modeling provides new insights on the nature of the Earth's largest structures in the deep interior, and their interaction with the surrounding mantle," Yuan said in a statement.

"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."

This article has been updated to include quotes from Qian Yuan and Mingming Li.