The discovery of gases released from deep beneath the Earth’s crust could help to explain Southern Africa’s unusual landscape, a study published in the journal Nature Communications suggests.
Scientists have long puzzled over why areas such as South Africa’s Highveld region are so elevated and flat, with unexpectedly hot rocks below the surface.
A team led by scientists from the University of Edinburgh analysed the chemical make-up of gas emerging from a deep crack in the Earth’s crust located in KwaZulu-Natal.
They found that variants of the elements helium and neon present in the gas match the composition of a rocky layer 1 000 km below Earth’s surface – called the deep mantle.
The findings provide the first physical evidence that Southern Africa lies on top of a plume of abnormally hot mantle, which had until now only been theorised using computer modelling of seismic data.
The researchers have determined that carbon dioxide-rich gases bubbling up through natural springs in South Africa originate from a column of hot, treacle-like material – called a hotspot – located deep inside the Earth.
Hotspots are known to generate volcanic activity in Hawaii, Iceland and the Yellowstone National Park, in the US.
In South Africa, the hotspot pushes the crust upwards, generating the distinctive landscape, which consists mostly of tablelands more than 1 km above sea level, the researchers say.
This also explains why rocks beneath the region are hotter than expected – a property that could be harnessed to generate geothermal energy.
The study was funded by the UK's Engineering and Physical Sciences Research Council and the Natural Environment Research Council and was led by Dr Stuart Gilfillan, of the University of Edinburgh’s School of GeoSciences.
“The high relief and hotter-than-expected subsurface temperatures of the rocks beneath Southern Africa had been a puzzle for geologists for many years. Our findings confirm that carbon dioxide gas at the surface is from a deep mantle plume, helping to explain the region's unusual landscape,” he commented in a press release issued on Tuesday.
The research was completed with support from Scottish Carbon Capture and Storage and the UK Carbon Capture and Storage Research Centre. It also involved scientists from the Universities of Aberdeen and Strathclyde, the Scottish Universities Environmental Research Centre, the British Geological Survey and The South African Council for Geoscience.