Science behind SA’s scary sinkholes
This gaping tear in the Northern Cape veld is the latest sinkhole to appear in SA. We look at the potentially lethal phenomenon
LIKE an ugly wound, the jagged gash in the ground stands in stark contrast to the ramrod-straight road that runs alongside it. No cars can drive past it now – it’s just too dangerous – but curious passers-by have been flocking on foot to peer into the yawning chasm.
This is the scene at Mount Carmel near Daniëlskuil in the Northern Cape where on 5 January a 100 m-long fissure suddenly appeared, posing a serious threat to motorists and prompting authorities to close the nearby R31 road. The hole, which at its widest measures 10 m and plunges 30 m deep, grew rapidly and at the time of going to print was almost 300 m long.
Experts fear this potential death trap could get even bigger. “Once a sinkhole or fissure occurs it can continue to destabilise and grow at an alarming rate,” explains Steven Walker, a University of Cape Town archaeologist who visited the site in search of artefacts.
The change to the landscape has been a long time coming, says Andries van Zyl, who along with his brothers owns the farm Mount Carmel where the hole appeared.
“Just before the ground opened we had heavy rains – 188 mm fell in three days,” he tells YOU. “The fissure has been slowly forming since about 2010. For a while it looked like a little stream running along the road.
“But this recent heavy rain made the ground finally give way.”
His farm is also the location of South Africa’s most famous and eeriest sinkhole, Boesmansgat. At 100 m wide and 270 m deep, it’s one of the six deepest freshwater caves in the world.
It came into existence thousands of years ago as a result of dolomite erosion and is the setting of many diving records – but Boesmansgat has also claimed the lives of three professional cave divers.
Despite the dangers sinkhole exploration poses, cave diver Karin Human and other members of the Speleological Exploration Club have already explored the new sinkhole at Mount Carmel as well as the caves below.
“It was an incredible experience,” Human says. “The cavities underneath the sinkhole have been named Rainbow Caves. After the devastating drought experienced in the area the rain that caused the fissure is a sign of hope, much like a rainbow.”
It seems Mount Carmel is on shaky ground. “In fact, I have another sinkhole that appeared right in the middle of my pastures,” Van Zyl says. He’s taken measures to cordon off the area to protect his cattle.
The region is such a hot spot for sinkholes and fissures because of its limestone deposit and extensive network of underground water, Walker explains.
“There’s a large dolomite deposit underneath this region and dolomite is something that’s eaten away by water.
Karstic formations (underground