Rising Land

A puzzling land upheaval in South Africa comes from an unexpected source

- Avery Schuyler Nunn

FOR DECADES GEOLOGISTS THOUGHT the slow rise of South Africa’s southern coast was driven by forces deep below—buoyant plumes of molten rock ascending through Earth’s mantle and heaving the crust upward over millions of years. But now satellite data and precise GPS measurements are tilting such assumptions off their axis. A study in the Journal of Geophysical Research: Solid Earth suggests this land rise may have less to do with deep tectonic forces and more to do with missing groundwater just under our feet.

Human activity has long been depleting South Africa’s groundwater. In 2018, after grappling with severe droughts for years, the country came close to a full-blown water emergency when Cape Town was nearly the world’s first major city to literally run out of water—a scenario dubbed “Day Zero.” For several months that year the city’s residents faced the very real prospect of having to regularly queue for critically limited water supplies, an outcome staved off only by timely rainfall and intensive water-saving campaigns. The extreme shortage resulted from a combination of climate change and unsustainable water use, which drained surface reservoirs and placed mounting pressure on aquifers across the region.

The recent study hypothesizes that the ground, once compressed by the sheer weight of the surface water and groundwater above it, is now expanding like a foam mattress relieved of pressure. Using GPS and satellite gravity data from between 2000 and 2021, the researchers detected a roughly six-millimeter rise in the land surface—a shift that coincides with humans’ depletion of South Africa’s water reserves and periods of drought.