Five more limestone stacks found near Twelve Apostles in Melbourne

[MELBOURNE] A popular Australian tourist attraction - a series of limestone stacks off the south coast known as the Twelve Apostles - could become a bigger draw after researchers said on Thursday (March 10) that they found five more columns under the sea.

The find, about six km offshore from the Great Ocean Road and 50 m below the surface, was discovered during sonar mapping of the sea floor off the Victoria state coast, University of Melbourne scientists said in findings published in the Journal of Coastal Research.

"This is the first of their kind (limestone stacks preserved in the ocean) that we've found so far," Dr Rhiannon Bezore of the university's geography department told AFP.

"When we did find them, it was quite a shock. They are pretty unique features and we don't expect to find sea stacks that are not eroded ... the fact that these are preserved at that depth is very unique."

The Twelve Apostles, a series of giant rock formations of different heights in the Southern Ocean off the Great Ocean Road about 230 km south-west of Melbourne, started forming 20 million years ago when erosion gradually began whittling away the nearby limestone cliffs.

But columns under the water are unusual as sea stacks usually erode and collapse as the sea level rises.

Dr Bezore said the five columns, dubbed the "Drowned Apostles" by scientists, likely dated back some 60,000 years.

They were preserved as that period was after a "glacial maximum" - a glacial period or ice age - when sea levels were rising "very very quickly... at least twice as quickly as the rate it is today", she added.

"The reason that they survived is because as the sea level rose after they were formed, it must have been rising at such a fast pace that they were submerged before the waves had the chance to erode them away and they collapse," she said.

One of the Twelve Apostles' limestone pillars, a 45-m rock pile, collapsed in 2005.

AFP