‘Drowned Apostles’ discovered in Victoria

By AG Staff Writer 9 March 2016
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Victoria’s iconic Twelve Apostles have received a surprise boost in numbers with the discovery of five extra limestone columns hidden deep underwater.

SONAR MAPPING OF the seafloor off Victoria’s southern coast has revealed never-before-seen sea stacks which scientists are dubbing the ‘Drowned Apostles’.

The five limestone stacks are located 6km off-shore from the Great Ocean Road and 50m beneath the water’s surface. While smaller in height and number than their iconic protruding cousins, the Drowned Apostles have surprised scientists with their defiance of normal erosion rates.

“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 the University of Melbourne’s School of Geography.

The original discovery from the sonar data was made by Rhiannon Bezore, a University of Melbourne PhD student. She said the Drowned Apostles 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,” said Rhiannon, who will present the paper in Coogee, Sydney on Thursday morning. The findings are published in the US-based Journal of Coastal Research.

Drowned Apostles

A diver near the Drowned Apostles, 50m underwater. (Image: Liz Rogers).

According to the researchers, the famous Twelve Apostles provide a contemporary analogue for the formation of the newly discovered Drowned Apostles.

“The Port Campbell Limestone along this section of coast has a maximum burial depth of close to 300m, so it is assumed that the drowned stacks are also made of limestone since they were found at only about 60m depth,” they stated in the paper.

“There is also no evidence that the submarine features are volcanic necks or pipes, as there is no igneous geology in the surrounding region,” they said.

The sonar data is part of a project to map the “reef estate” in Victoria, which supports commercial fisheries for southern rock lobster and abalone.

“We are only just starting to understand the biodiversity value of these deep reefs which harbour diverse invertebrate communities, many unknown to science,” said Dr Daniel Ierodiaconou from Deakin University, who provided the high resolution sonar data in which the Drowned Apostles were discovered.

The data was captured using advanced multi-beam sonar technology.