South Australia's south east cluster of 20 water-filled ancient sinkholes a major diving attraction

The concentration of water-filled sinkholes in South Australia's south east, near Mount Gambier, has attracted worldwide attention.
Image courtesy ABC

South Australia’s south-east Limestone Coast region around Mount Gambier has about 50 sinkholes, one of Earth’s largest concentrations. Twenty of those sinkholes are cenotes: filled with water, because they're below the water line.

The sinkholes have been formed from the Limestone Coast’s long-term exposure to ocean water and waves that have created many large caves, with their entrances blocked off by erosion and caveins. When the ceiling of the cave collapses, a sinkhole is formed.

Fossil Cave (formerly The Green Waterhole), at Tantanoola, about 22 kilometres from Mount Gambier, is largely filled with water and, during the 1960s-80s, divers from the South Australian Museum, South Australian Underwater Speleological Society, Flinders University Underwater Club and Allum and Garrad first surveyed the 30-million-year old Oligocene coralline limestone site.

Pleistocene subfossil material of birds and mammals, from 15,000 to 40,000 years ago, was found to a depth of about 15 metres. The fossils represent many living animals but also extinct species including the birds Centropus colossus and Orthonys hypsilophus, mammals Thylacinus cynocephalus and Propleopus oscillans, Macorpus titan and kangaroos Procoptodon gilli and Simosthenurus occidentalis.

Access for cave diving is limited to holders of the Cave Divers Association of Australia’s advanced grade. The association has also worked closely with the fourth-generation Kilsby family whose sheep farm near Mount Gember is home to one of the deepest and clearest sinkholes, renowned worldwide. The family has welcomed divers since the 1950s and the Kilsby sinkhole is used for South Australian police divers annual exercises. It has even by used by the federal government for weapons research into sonobouy monitors.

Other water-filled sinkholes near Mount Gamier include the three at Ewen Ponds, and the Little Blue Lake. Not water-filled, but another south-east sinkhole attraction, is the Umpherston, also near Mount Gambier, that has become a spectacular sunken garden.


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