‘We had to check what we where seeing’ says Rhiannon Bezore, a PhD student at the University of Melbourne. ‘No one has seen stacks submerged at this sea level before.’
Reaching up like fingers on a hand, five new additions to the iconic Twelve Apostles were found 50 metres below sea level, ranging between three to six metres high. Using high-resolution sonar mapping, Bezore, along with Dr Daniel Ierodiaconou at Deakin University, detected the stacks while looking for ancient offshore features such as submerged cliffs or river channels as part of a project to map the topography of Victoria’s coastal sea floor.
‘I happened to spot these features fairly close to the current Twelve Apostles. They looked remarkably similar to sea stacks,’ she recalls. ‘After showing the data to my supervisors, we confirmed that they were indeed sea stacks.’
The stacks have been dubbed the ‘Drowned Apostles’ by scientists and they are understood to be the first examples of limestone stacks preserved in the deep ocean. ‘Sea stacks are generally temporary coastal features,’ says Bezore, ‘with a lifespan of 100 to perhaps 1,000 years.’ This is true of the original Apostles which, over a few hundred years, have eroded from the limestone headland to form nine stacks (despite the titular ‘twelve’). Indeed, as recently as 2005, the number was reduced once more to eight when a stack collapsed into the sea.
‘Only a very fine balance can create sea stacks,’ says Ierodiaconou. ‘The rock needs to be soft enough to erode quickly from a cliff but hard enough to support a rocky pillar.’ The five new stacks, however, have endured the deep sea conditions remarkably well and are thought to date back 60,000 years.
This was published in the May 2016 edition of Geographical magazine.