African Superplume Linked to Unusual Rift-Parallel Motion in East Africa

Computer models are helping scientists explain a puzzling pattern of ground deformation in the East African Rift System: motion running parallel to the rift, not just across it. The research points to the African Superplume, a vast upwelling of hot mantle material deep inside Earth, as the source, backed by how seismic waves travel through the rock below.

Continental rifting happens as Earth's rigid outer shell, the lithosphere, stretches and thins. Virginia Tech geophysicist D. Sarah Stamps compares its behavior to Silly Putty: hit it with a hammer and it cracks, but pull it slowly and it stretches. Most rifts show their strongest deformation perpendicular to the rift, as expected, and so does the East African Rift System, the largest continental rift system on Earth. But after more than 12 years of GPS measurements, Stamps's team found unexpected motion parallel to it.

In a study in the Journal of Geophysical Research, first author Tahiry Rajaonarison, a postdoctoral researcher at New Mexico Tech who earned his Ph.D. at Virginia Tech in Stamps's lab, built 3D thermomechanical models to investigate the cause. The simulations show the rift-parallel motion is linked to northward mantle flow from the African Superplume, a rising zone of mantle material beneath southwest Africa that extends northeastward and grows shallower heading north. The models also reproduced matching rift-parallel seismic anisotropy, where seismic waves travel differently by direction because rock minerals have aligned.

Stamps first spotted the unusual motion as a postdoctoral researcher, using GPS stations tracking signals from more than 30 satellites roughly 25,000 kilometers above Earth, precise enough to measure surface motion at the millimeter scale. A 2021 study had shown near-surface lithospheric buoyancy forces explained the expected perpendicular deformation but not the parallel motion, leaving researchers searching for another mechanism.

"We confirmed previous ideas that lithospheric buoyancy forces are driving the rift, but we're bringing new insight that anomalous deformation can happen in East Africa," Rajaonarison said.