Melbourne: Five extra limestone columns hidden way below the water have been discovered in Australia, giving a boost to the iconic tourist attraction Twelve Apostles.
The never-before-seen sea stacks, located six kilometres offshore from the Great Ocean Road and 50 metres beneath the water's surface, were found by researchers during sonar mapping of the seafloor off Victoria's southern coast.
Scientists are dubbing them the "Drowned Apostles."
While they are smaller in both size and number than their more famous cousins, their existence alone is remarkable given their defiance of normal erosion rates, researchers said.
This is the first time such limestone stacks have been found preserved in the ocean.
"Sea stacks are always eroding, as we saw with the one that collapsed in 2005, so it is hugely surprising that any could be preserved at that depth of water," said David Kennedy from University of Melbourne.
"They should have collapsed and eroded as the sea level rose," said Kennedy.
Like the Twelve Apostles, the newest additions were once part of larger limestone sea cliff, researchers said. Rhiannon Bezore, from University of Melbourne, who made the initial discovery in the sonar data, said they probably date back 60,000 years.
"We had to check what we were seeing because no one has seen stacks submerged at this sea level before," she said.
"Only a very fine balance can create sea stacks, with rock needing to be soft enough to erode quickly from a cliff but hard enough to support a rocky pillar," said Daniel Ierodiaconou from Deakin University in Australia.
The sonar data was collected using the latest advances in multi-beam sonar technology.
The findings were published in the Journal of Coastal Research.