Get more Mail & Guardian
Subscribe or Login

Satellites could fill in where sinkhole studies fall through

Age lies heavily on the abandoned mine shaft, its stale air thick and leaden in the darkness. Decades ago, it was a bustle of activity, with hunched men digging coal out of the blackened walls and carrying it to the surface about 10 metres above their heads.

Today, it sits empty and hollow as the supporting pillars begin to sag with each year. Tufts of grass have begun to grow above it, and many have forgotten that there was once a mine there, until one day the roof of the mine collapses and sucks the surface into its belly.

"Surface deformation due to underground mining poses risks to health and safety as well as infrastructure and the environment," explained Dr Jeanine Engelbrecht this week. She recently completed her PhD at the University of Cape Town in techniques to detect mining-related land subsidence. "Sometimes mining companies are aware [of potential subsidence], but when they don't expect surface subsidence, it can cause serious damage to infrastructure and roads."

Meanwhile, an orbiting satellite is bouncing signals off the earth's surface to detect where this will happen. Engelbrecht, now based at the Council for Scientific and Industrial Research's ICT Meraka Institute, is using these data to predict possible subsidence on South Africa's surface.

"We used earth orbiting satellites [transmitting and receiving] microwave signals to accurately measure the earth's surface," Engelbrecht said. For her PhD, she used this technique on an area that had been an underground coalmine, but cannot disclose which mine due to a confidentiality agreement. The data, captured by European, Japanese and Canadian satellites, can measure surface deformation in terms of millimetres.

'Novel' technique
Engineering geoscientist Dr Souleymane Diop, based at the Council for Geoscience, said this "novel" technique is "the X-ray you get when you go to the doctor", while the work he does is the biopsy: "We do ground geophysics and then invasive techniques, like drilling, to confirm that there is a void, with the potential of caving in."

He indicates the Witbank area, where there are many old coal mines, as a site of major land subsidence.

But traditional mining-related subsidence is only one part of what Diop's team at the council looks at: "Subsidence can happen for many reasons," he said, such as dolomitic land (where the ground comprises dolomite, a kind of rock that can be dissolved by slightly acidic water), acid mine drainage, swelling clay and illegal mining.

In some cases, old mines used timber to support the ceiling, and those supports have rotten away. In others, the long-dead miners left pillars of coal to stop the roof from caving in, but now "illegal miners go in and mine the pillars as well", Diop said.

At the Meraka Institute, Engelbrecht is developing her PhD work on these satellite techniques for earth observation to include "not just mining, but also areas prone to sinkholes and geological hazards".

Lee Annamalai, earth observation competency manager at the institute, said Engelbrecht is "coming with the domain knowledge from a geological point of view … I want to add steroids to the work that she's doing and turn in from research work into practical solutions for customers, [such as] mines, the environmental community interested in dune erosion, various air forces [to] monitor sinkholes on the air force's bases."

The Meraka Institute, with just over 200 staff, has a track record of innovative ICT solutions, such as its Advanced Fire Information System (AFIs) which tracks fires in real time.

But, unlike the publicly available AFIs offering, "we still haven't worked out if we'll have a publicly accessible map [for surface deformation] … but there are interesting applications we want to investigate", Annamalai said.

Subscribe for R500/year

Thanks for enjoying the Mail & Guardian, we’re proud of our 36 year history, throughout which we have delivered to readers the most important, unbiased stories in South Africa. Good journalism costs, though, and right from our very first edition we’ve relied on reader subscriptions to protect our independence.

Digital subscribers get access to all of our award-winning journalism, including premium features, as well as exclusive events, newsletters, webinars and the cryptic crossword. Click here to find out how to join them and get a 57% discount in your first year.

Sarah Wild
Sarah Wild is a multiaward-winning science journalist. She studied physics, electronics and English literature at Rhodes University in an effort to make herself unemployable. It didnt work and she now writes about particle physics, cosmology and everything in between.In 2012, she published her first full-length non-fiction book Searching African Skies: The Square Kilometre Array and South Africas Quest to Hear the Songs of the Stars, and in 2013 she was named the best science journalist in Africa by Siemens in their 2013 Pan-African Profiles Awards.

Related stories


If you’re reading this, you clearly have great taste

If you haven’t already, you can subscribe to the Mail & Guardian for less than the cost of a cup of coffee a week, and get more great reads.

Already a subscriber? Sign in here


Subscribers only

Fears of violence persist a year after the murder of...

The court battle to stop coal mining in rural KwaZulu-Natal has heightened the sense of danger among environmental activists

Data shows EFF has lower negative sentiment online among voters...

The EFF has a stronger online presence than the ANC and Democratic Alliance

More top stories

Eastern Cape premier Mabuyane lives large amid province’s poverty

Oscar Mabuyane and MEC Babalo Madikizela allegedly used a portion of state funds for struggle icon Winnie Madikizela-Mandela’s commemoration for their own benefit

Constitutional court confirms warrantless searches in cordoned off areas unconstitutional

The law was challenged in response to raids in inner Johannesburg seemingly targeting illegal immigrants and the highest court has pronounced itself 10 days before an election in which then mayor Herman Mashaba has campaigned on an anti-foreigner ticket

A blunt Mantashe makes no promises during election campaigning

ANC chairperson Gwede Mantashe told people in Daveyton to stop expecting handouts from the government

Mbeki: Social compact the answer to promises made in ANC...

Former president Thabo Mbeki urged business and government and society to work together to tackle issues such as poverty, unemployment and poor services and infrastructure

press releases

Loading latest Press Releases…