A North Ballarat family was alarmed when a depression in their backyard collapsed to reveal a sinkhole at the weekend.
The hole roughly a metre, by a metre and half, fell in while Andrew Rolt was trying to fill in the depression.
No cause has yet been identified, although it is highly unlikely to be a collapsed mine shaft given the property’s North Ballarat location.
Ms Ryan said surveyors looked at the hole a year ago when the ground first dropped.
“They said it could be one in 20,000 things, but they didn’t think it was too much,” she said.
“We assumed it was a little hole.
“My husband got down to cut it out, so we could pour earth in, and it all just gave way.”
Ms Ryan said she initially did not know who to contact to resolve the situation.
The couple has owned the 13-year-old home for three years.
Civil engineering firm Colin McClelland & Associates inspected the hole when it first appeared last year.
The firm’s Michael Lang said they were yet to look at the most recent collapse, but there were a number of likely options.
“It could be anything from decomposing tree matter, old tree stumps, buildings and septic tanks caving in,” he said.
“We can’t rule out mine shaft – but it is unlikely in this area – we could not find anything in any mine maps, and it was a smaller depression.
“We will do some more testing to see what we can see.”
Old mine shafts were historically covered with timber sleepers, which eventually deteriorate over time, before they cave in.
Some areas have details maps of former mine shafts and tunnels.
Ms Ryan said filled in watercourses could have caused the hole.
“Maybe it was rubble, that filled in the space and has shifted,” she said.
“I believe there has been a lot of watercourses running through there previously.”
Buninyong Community Reserve, which was built over a creek in the 1980s, also had a sinkhole open up in November last year.