An Australian couple who lost their belongings in the 2011 Brisbane floods are counting themselves lucky after a giant sinkhole opened up in their backyard.
Engineers and a mining company have spent the past day at the home of Ipswich pensioners Lynn and Ray McKay after a huge sinkhole full of water opened up near Lynn's clothesline.
Mrs McKay told Checkpoint the hole opened up suddenly.
"Our neighbour was out in his back yard and he heard this big bang and he turned around and here was this hole in our backyard and he came and said to us 'do you know you have a hole in your back yard?'."
She said she was very happy with mayor's help and they lived in a small community where people looked after each other.
"I'm not really sure what the real go is at the present, so we're just playing things by ear."
She said the water was now being pumped out, and she only had one worry.
"I don't want them to take my clothesline. It's not far from the clothesline. That's one thing I want to save."
University of Queensland's Occupational Health and Safety in Mining Professor David Cliff said the site was unstable, with water eroding the surrounding topsoil.
"The concern is that this hole could get much bigger if the water in that hole has destabilised the strata underneath the surface," he said.
"There must be some potential for it to get bigger."
Authorities have ruled out a burst water pipe, with sights now turned to investigate whether a vertical mine shaft was responsible.
Geotechnical engineers will return to the Coal Street home today.
Professor Cliff said a geological inspection with radar or sonar was needed to determine the cause.
It would look at density differences to detect cavities and water flow then map underground contours to look for solids and gaps.
Professor Cliff said it was possible a pillar that held up the roof and strata above the coal seam collapsed, causing the sinkhole.
"It's possible over time those pillars lose their strength then the roof will collapse," he said.
"They'd have to identify what's causing it and the likelihood of the hole progressing to any bigger size."
Professor Cliff was surprised to see water in the sinkhole, as generally old underground workings were dry.
"[There may have been] a subterranean creek or river flowing which has caused the erosion so the top soil suddenly collapsed."
Restless night for the McKays
Mayor Paul Pisasale said the homeowners, who have lived at the property for 25 years, had a restless night in a hotel.
He returned with them to their home early this morning.
He said the water inside the hole would be tested for contamination before it could be discharged.
"I thought this couldn't be happening," Mr McKay told Nine News.
"It is devastating. It's grown a bit bigger, some fell in before since we have been here."
The couple lost everything in the 2011 floods.
"We were just getting back on track. Things were going very well," Mrs McKay told Nine News.
Stabilisation needed to prevent further growth
The Department of Natural Resources and Mines is determining an appropriate method to pump and dispose of water from the sinkhole.
Professor Cliff said if an old mine caused the sinkhole, engineers would need to fill the adjacent areas to prevent the hole getting bigger.
"You can try backfilling, historically in Ipswich they've put lots of concrete into holes to try and block them all up," he said.
"[Or] you can bridge over the top. It may be more effective. What you can do it put a cap a few metres below the surface and then just fill on top of that.
"It depends on what's underneath, how stable the sub-strata is."