Zambia's hot springs offer a clue to tectonic activity in southern Africa. By analyzing gases bubbling to the surface, researchers detected helium isotopes typical of the Earth's mantle, located tens of kilometers (tens of miles) deep. This discovery proves that an underground fault is active and that a new rift may be forming. If this process continues, it could eventually split the continent in two.
A rift is a huge crack in the Earth's crust, often accompanied by magma upwellings. If activity persists, it can evolve into a tectonic plate boundary and even give rise to an ocean. But most rifts stop before this stage. The Kafue Rift in Zambia is part of a 2,500‑kilometer (about 1,550‑mile) long system linking Tanzania to Namibia, with a possible connection to the Mid-Atlantic Ridge. Researchers are interested in it because of its unusual landscape and numerous hot springs.
Credit: Prof Tom Gernon, University of Southampton Scientists sampled gases from eight geothermal wells and springs, six of them in the suspected area, to confirm that a rift is forming. In the laboratory, they measured helium isotope ratios. Professor Mike Daly of the University of Oxford, co‑author of the study published in
Frontiers in Earth Science, explains that these signatures indicate a direct connection to the mantle, located between 40 and 160 kilometers (about 25 to 100 miles) deep. This observation is proof that the Kafue fault is active.
The results are similar to those seen in the East African Rift System, a much older and better‑studied rift. Springs located outside the Kafue zone do not show the same signatures. The researchers also detected carbon dioxide in amounts consistent with mantle‑derived fluids. According to them, helium is an early indicator of rifting, and over time CO₂ emissions should increase as volcanic activity develops.
This geological activity could have interesting economic implications. Early‑stage rifts offer potential for geothermal energy. They may also harbor underground reserves of helium and hydrogen, gases increasingly in demand for modern technologies. Unlike active volcanoes, the gases from these rifts are less diluted, making their extraction easier.
Location of the extension zone within the Central African plateau of Zambia. Samples taken in the rift zone include geothermal wells (wells 15, 18 and 20) and springs (Bwengwa and Gwisho). Basement hydrothermal spring samples were taken approximately 50 km (31 mi) southwest (Mosali spring) and approximately 150 km (93 mi) north‑northwest (Lubungu spring) of the rift zone. Location of other thermal springs (Legg, 1974; Tamburello et al., 2022).
The discovery also changes the view of Africa's future evolution. Until now, the Great East African Rift Valley was considered the primary candidate for a future split of the continent. But its progression is slow, hindered by the constraints of the surrounding oceanic ridges. The southwest African system exhibits faster fracturing, with natural weaknesses in the crust that could facilitate rupture.
Scientists urge caution. This preliminary study covers only a limited area of the southwest African rift system, which extends for thousands of kilometers (thousands of miles). Further research is underway, with results expected this year.