I found this to be interesting and didn't know that we had a town nearby that had this problem...
Scientists have identified Australia's problem locations for sinkholes
Sinkholes are sudden, catastrophic, and almost entirely unpredictable and one Australian city sits on a rabbit warren of potential sinkholes.
THE ANATOMY OF A SINKHOLE
Bechtel explained to Sunday Night that if your home happens to be built over limestone, beneath it the ground will be “like Swiss cheese” and riddled with caves. Groundwater dissolves the limestone until, in the right conditions, all it takes is heavy rain or a faulty sewer to trigger a dramatic and dangerous sinkhole.“A sinkhole is basically a hole underneath the ground that is slowly eating its way up. The roof gets higher and higher until the weight of someone walking over the top or a truck driving over collapses the roof.
WHAT ABOUT AUSTRALIA?
Mount Gambier is one of a very small handful of places in the world with the soft limestone bedrock that creates deep, circular, spectacular sinkholes like the ones found in Mexico and Florida.Beneath the regional centre of Mount Gambier is a myriad of caves. According to Aussie geologist and sinkhole buff, Ian Lewis, the only things keeping them from collapsing are the dry conditions and relatively stable water table.“Mount Gambier only has a population of 20,000, but if you built a city there with a few million people, it would be the next Florida," Lewis said.