A Single Superplume is Splitting Africa

Africa is splitting in two. The reason: a geologic rift runs along the eastern side of the continent that one day, many millions of years in the future, will be replaced with an ocean. Scientists have argued for decades about what is causing this separation of tectonic plates. Geophysicists thought it was a superplume, a giant section of the earth's mantle that carries heat from near the core up to the crust. As evidence, they pointed to two large plateaus (one in Ethiopia and one in Kenya) that they said were created when a superplume pushed up the mantle. Geochemists were not able to confirm that theory. Instead they thought there might be two small, unrelated plumes pushing up the plateaus individually. The theories did not align, says David Hilton, a geochemist at the Scripps Institution of Oceanography in La Jolla, Calif. “There was a mismatch between the chemistry and the physics.”

So in 2006 and 2011 Hilton headed to East Africa to see whether he could lay the argument to rest. He and his team decided to use gases emanating from the rift to determine how it was created. Donning gas masks, they hiked to the tops of volcanoes in Tanzania and Ethiopia and climbed into mazuku (the Swahili word for “evil wind”)—geothermal vents and depressions where deadly gases accumulate and often kill animals. At these locations, the team collected samples of rocks deposited during eruptions, including olivines, crystals that trap volcanic gases like a bottle.

Back home in California, Hilton crushed the rocks inside a vacuum to release their gases. He was looking for helium 3, an isotope of helium present when the planet was forming that was trapped in the earth's core. Hilton figured that if rocks around both the Ethiopian and Kenyan plateaus contained this primordial gas, that would at least confirm that underground mantle plumes created them. The readings showed that, indeed, both plateaus contained helium 3. But Hilton and his group still had to wonder: Was one superplume behind it all? Or were there a couple of lesser plumes?

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Well, James, there's no need to go to the Moon!  Let's strip mine the Olduvai Gorge for Helium-3!