Sinkhole

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Sinkholes are cavities in the ground that are formed when groundwater dissolves underlying soluble rock layers. A considerable part of Gauteng province is underlain by dolomitic formations,¹ a soluble carbonate rock which is highly susceptible to erosion when groundwater levels change. Sinkholes do occur as part of the slow, natural process of erosion over thousands of years but human activity has been recorded to trigger and accelerate the process. Rainwater (H2O) absorbs carbon dioxide (CO2) from the atmosphere and soil (where the concentration of this gas may be up to 90 times greater than in the atmosphere) to form a weak carbonic acid (H2CO3).² The subsequent dissolution by percolating groundwater that circulates along tension fractures, faults, and joints in the dolomitic succession have led to the formation of caves and voids in the rock. When the underground water level changes - by natural or as a consequence of mining - the overlying materials collapse into the underlying voids: a sinkhole has been created.
        Sinkholes are usually unpredictable and can be catastrophic, particularly when they are sufficiently large, sinkholes cause property damage or loss of life.  Human activity is a major cause of sinkholes, especially in the Gauteng region where gold mining was historically the basis of the economy and socio-economic development.³ The byproducts of extensive mining operations was the extraction of massive quantities of groundwater to dig mine shafts that contributed to ground instability. Despite waning mining activity as a result of depressed gold prices since the 2008 global financial crisis and increasingly-more expensive investments needed to extract gold (since most of the readily accessible gold has been already extracted),⁴ the risk of sinkholes is expected to increase.

Image source:  Oosthuizen, Johannes Marthinus. ¨Picture of the sinkhole, at the Blyvooruitzig mining village that claimed the lives of the Oosthuizen family¨. Wikitree. Accessed March 5, 2022.https://www.wikitree.com/photo/jpg/Oosthuizen-1433-1