The risk of sinkholes forming without warning is a concern in many inhabited areas all over the world. A massive sinkhole recently appeared near Danielskuil in the Northern Cape Province. Sinkholes form in areas where soluble rocks below the surface, like limestone or dolomite, are dissolved by water. These processes form cavities or caves below the Earth’s surface and sinkholes occur when the surface collapses into these cavities. The sinkhole at Danielskuil is an example of these natural geological processes. In fact, certain areas in the Northern Cape are known for their underground caverns and these are frequented by spelunkers and explorers.

Although these natural features provide unique opportunities for scientific investigation, they pose a terrifying risk to lives and infrastructure on the surface area. Therefore, in-depth geotechnical investigations are usually performed to identify areas where development should be avoided. However, these investigations can be labour-intensive and time-consuming, especially in large and remote areas like the Northern Cape.

The CSIR has developed a system to rapidly detect the deformation of land surfaces in an effort to spot sinkholes as they develop. This system, dubbed Azimuth, demonstrated the ability to detect small-scale movements of the earth’s surface using special radar sensors on-board earth-orbiting satellites. The data captured by the satellites are processed and the researchers have written algorithms that map deformations at the scale of millimetres to centimetres. The new system monitors, operationally, large areas of South Africa that are at risk of movements.

Although we currently focus on detecting collapses in mining areas, we were recently able to detect surface movements before sinkhole collapses in the Gauteng area. The findings prove that such satellite data, if captured routinely, can provide early warning of sinkholes before they happen. This will allow us to minimise the danger to life and property. Azimuth can provide valuable information in areas prone to sinkhole formation.

This brings us to the detection of movement in the case of the Danielskuil sinkhole. Capturing the satellite data at regular intervals is expensive. We have therefore focused on areas with a high probability of experiencing movement and areas that are vulnerable such as densely populated areas. For this reason we have been focusing on mines and dolomite areas in Gauteng. However, with the recent increase in sinkhole activity in the Northern Cape, there is a unique opportunity to commission new data acquisitions in the vicinity of Danielskuil to monitor ongoing movement. This data will be valuable to see in what direction the sinkhole will expand, especially since continued growth will threaten the R 31 between Danielskuil and Kuruman.

Azimuth will continue to collect data and provide information on the stability of the surface over large areas in South Africa. The ideal is to provide coverage over all areas in South Africa that has a risk of movement due to natural or man-made causes. This includes mining but also areas that are prone to sinkholes, landslides and swelling clays. By providing early warnings of areas that are unstable, we hope to make a valuable contribution to minimise the risk to lives and property. In this way, our small-scale measurements can have a massive impact.

For technical enquiries, please contact Dr Jeanine Engelbrecht, on 021 888 2447 or email JEngelbrecht@csir.co.za

For media related enquiries, please contact Mr Tendani Tsedu, Group Manager: Communications and Stakeholder Relations, on 012 841 3417/082 945 1980 or email mtsedu@csir.co.za