Authorities are plugging chasms in the NSW seaside suburb of Swansea Heads in a bid to save homes from two sinkholes that opened up without warning.
The first hole appeared on Tuesday night on plush Lambton Parade, south of Newcastle, where it threatened the front corner of one house.
By Wednesday morning, a second sinkhole had appeared in the front garden of a property two doors down.
The area underneath the neighbourhood was once part of the Swansea Pit, a coalmine that was abandoned in the 1950s.
The NSW Mine Subsistence Board is behind the investigation into the sinkholes, and on Wednesday night was pouring concrete into the pits.
The head of the board, Greg Cole-Clark, says home owners will be compensated for the damage to their properties, and authorities had no "undue concern" for neighbouring houses.
"We are now in the process of securing the site," Mr Cole-Clark told Fairfax Media.
"There are mine workings under the site. They were abandoned about 1953.
"At this point in time, we assume they're about 25 metres in depth.
"There has been no history of mine subsidence in this area for 60 years or more."
Stephen Fityus, a professor of geotechnical engineering at Newcastle University, said old mine workings were dotted about the coal-rich Hunter region.
He said some were dug one atop the other, meaning some voids stretched two or even three levels down.
But while plenty of locals were familiar with the "dips" these old mine facilities could cause, larger sinkholes such as those that have opened up at Swansea Heads were less common.
"Potentially, as many as half the houses in the geographical bounds of the city of Newcastle are undermined by old mine workings," Prof Fityus told AAP, and that includes his own home.
"I'm less than 20 metres above an abandoned (mine site) ... but it's not going to pose a significant threat to me and my family in our lives."
Share
