beach erosion
© Surf Life Saving QueenslandThe beach is popular with anglers but no-one was there when the sand collapsed.
A hole "almost the size of a football field" has opened up at Jumpinpin bar on North Stradbroke Island, off south-east Queensland.

Senior lifeguard Michael Bates said the beach had collapsed on the southern side of the island this morning.

It is a popular spot for fishing and four-wheel-driving but no-one was on the beach at the time.

Mr Bates said the erosion had created dangerous conditions.

"It is a little bit smaller than a football field," Mr Bates said.

There is still a question mark over how big the hole will get.

"It is almost like a swirling effect in the water that is created by the change of tides and there is unstable sand in the area," Mr Bates said.

"It is not a safe areas for swimming area at all, due to it being so unstable, unpredictable and varying depth and the strong water movement.

"It is going to make it a very massive hazard."

University of Queensland researcher Konrad Beinssen said sinkholes were common at Jumpinin.

beach sinkhole
© Brooke ByrneA ledge could be seen at Jumpinpin bar a month ago, before the hole opened up.
Mr Beinssen, who wrote a research paper on a sinkhole that opened up at Inskip in southern Queensland in September, said the conditions were right at Jumpinin.

He said the sand was the right consistency, fine and densely packed on an underwater slope.

"They grow by positive feed back," he said.

"They get bigger and bigger and bigger as they retrogress towards the coast.

"They occur when an underwater sand cliff retrogresses backwards and sometimes it reaches the shore and collapses the beach."