Another five limestone stacks have been discovered offshore from Victoria's Great Ocean Road near the famous Twelve Apostles landmarks.
This is the first time that submerged limestone stacks have been found anywhere in the world. The "drowned Apostles", as scientists have dubbed them, were found this month by Melbourne University PhD student Rhiannon Bezore and her co-supervisors, geomorphologist David Kennedy and Deakin University's Daniel Ierodiaconou, during sonar mapping of the reef.
"We were looking for other submerged features - drowned cliff lines, possible river channels or estuary basins under the sea - and then we found these features that looked remarkably similar to sea stacks," says Bezore. "We all had to make sure we were looking at what we thought we were looking at. We definitely weren't expecting to make such a cool discovery."
The stacks are 12 kilometres west of the other Apostles (between Port Campbell and Peterborough). The five columns are submerged 50 metres below sea level, average five metres in height and are thought to be part of a larger limestone sea cliff dating back 60,000 years. The Twelve Apostles, now only eight columns after a fourth collapsed in 2005 (the number is disputed following a partial collapse in 2009, but the researchers count eight), average 45 metres in height.
Bezore says the submerged sea stacks were eroded out of the cliff side in a similar process to the Twelve Apostles, and that they were preserved thanks to rapid rises in sea level shortly after being formed.
"The sea level must have been rising at such a rapid rate that the waves and wind didn't have a chance to completely erode them away," she says. "Now that they're submerged completely, they will most likely be there long term."
While collecting rock samples for analysis, divers have discovered deep-sea reefs on top of the stacks and an abundance of marine life.
"It's definitely opened up a window to look for these features in other locations," says Bezore. "Until now, no one really thought to look for them as they weren't really thought to exist."
Thinking of visiting the Great Ocean Road? Here's our guide to the area.