Deep beneath the Earth’s surface, in a layer called the mantle, heat builds up and pulses, causing rock to slowly rise toward the crust. This movement is known as a mantle upwelling, and it plays a major role in forming volcanoes, breaking continents apart, and even creating new ocean basins.

In East Africa, the Afar Depression is famous among geologists because it’s one of the few places on the planet where three divergent plate boundaries meet – the Main Ethiopian Rift, the Red Sea Rift, and the Gulf of Aden Rift.

Scientists have long suspected the presence of one of these upwellings. But its exact shape, composition, and how it interacts with the shifting plates above remained unclear.

While the region’s volcanic activity and frequent earthquakes have long hinted at a hot mantle plume pulsing up from deep below, new research provides the clearest picture yet of its structure and behavior.

Mantle pulses from deep Earth

To learn more, researchers led by the University of Southampton collected lava samples from over 130 relatively young volcanoes across the region.

By analyzing the chemistry of these rocks and combining their findings with existing geological data, they discovered that the upwelling beneath Afar isn’t simple or uniform.

It’s asymmetrical and made up of plumes and various types of hot mantle material – almost like a patchwork, rather than a single stream.

Emma Watts, the study’s lead author, began the project at Southampton and now conducts research at Swansea University.

“We found that the mantle beneath Afar is not uniform or stationary – it pulses, and these pulses carry distinct chemical signatures,” she said. “These ascending pulses of partially molten mantle are channeled by the rifting plates above.”

Because those plates are stretching and thinning, the hot material can creep upward more easily, weakening the crust further and accelerating the birth of a new ocean basin.

Mantle pulses like a heart

Co-author Tom Gernon, a professor at Southampton, likens the chemical striping to a cardiovascular rhythm.

“The chemical striping suggests the plume is pulsing, like a heartbeat,” Gernon said. “These pulses appear to behave differently depending on the thickness of the plate and how fast it’s pulling apart.”

What’s particularly interesting is how this upwelling behaves differently depending on what’s happening above it.

In places where the Earth’s crust is pulling apart quickly – like the Red Sea Rift – the mantle flow is faster and more focused. In slower-moving areas, the upwelling spreads out more gradually.

Tectonics drive mantle flow

By tying mantle chemistry to plate dynamics, the study reshapes thinking about how continents fracture.

“We have found that the evolution of deep mantle upwellings is intimately tied to the motion of the plates above,” said co-author Derek Keir, affiliated with both Southampton and the University of Florence.

That coupling, he adds, influences “surface volcanism, earthquake activity, and the process of continental breakup.”

The observed plume is eroding the lithosphere – Earth’s rigid outer shell – from below, thinning it to as little as 15 kilometers in places. When combined with stretching from plate motion, that thinning triggers periodic volcanic episodes.

Active lava flows spilling out of the Erta Ale volcano in Afar, Ethiopia. Click image to enlarge. Credit: Dr Derek Keir, University of Southampton/ University of Florence

Lava flows blanket wide swaths of Ethiopia, while seismic swarms mark places where new crust is forming. Eventually, researchers say, seawater will flood in.

The Horn of Africa will split from the mainland, like the Atlantic did from Europe and North America.

Forecasting Earth’s deep forces

Large igneous provinces, like the North Atlantic Igneous Province, formed Northern Ireland’s Giant’s Causeway 60 million years ago.

Scientists blame them for climatic upheavals due to the vast volumes of CO2 and SO2 they release. Some may have even triggered mass extinctions.

Understanding the tempo of the Afar plume, therefore, has ramifications that reach beyond regional geology.

Mantle “heartbeats” elsewhere could explain past volcanic bursts and sudden environmental changes in Earth’s history.

A succession of volcanic deposits at Boset Volcano in the Main Ethiopian Rift. Click image to enlarge. Credit: Prof Thomas Gernon, University of Southampton

Researchers plan to map mantle flow beneath thin plates and how it directs volcanic vents in future studies.

“The work shows that deep mantle upwellings can flow beneath the base of tectonic plates and help to focus volcanic activity to where the tectonic plate is thinnest,” Keir explained.

“Follow-on research includes understanding how and at what rate mantle flow occurs beneath plates.”

Solving Earth’s deep puzzle

“Working with researchers with different expertise across institutions, as we did for this project, is essential to unraveling the processes that happen under Earth’s surface and relate it to recent volcanism,” Watts concluded.

“Without using a variety of techniques, it is hard to see the full picture, like putting a puzzle together when you don’t have all the pieces.”

In short, the study shows that mantle upwellings aren’t just deep Earth features operating in isolation. They’re actively shaped and guided by the movement of tectonic plates above, creating a dynamic connection between the deep Earth and the surface we live on.

For now, scientists can at least hear the planet’s mantle pulses beneath Ethiopia – a rhythmic signal of forces playing out deep below Earth’s surface, slowly ripping apart a massive continent and sketching the outlines of an ocean yet to be born.

The study is published in the journal Nature.

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