A South Australian hydrogeologist is seeking evidence that unusual reefs off the Limestone Coast may be linked to underwater volcanic activity. Ian Lewis said three irregular reefs, identified about 60 years ago during oil and gas surveys, run at right angles to the coast near Beachport.
The reefs are about 20 kilometres offshore, in water reaching depths of up to 45 metres. Mr Lewis said one possibility was that they were not limestone reefs but another type of rock, potentially lava flows from a submarine eruption.
He has also connected the theory to South Australia's largest recorded earthquake, in 1897, asking whether the event could instead have involved an undersea eruption. Mr Lewis described the idea as having remained largely speculative among geologists, and said samples would be needed to test it.
He hopes to lead a team of divers to the site to collect and examine rocks. He said anecdotal reports from fishers of small bubbles rising near the reefs could provide another clue, and that capturing gas for testing might help establish whether it was volcanic.
Diver Josh Richards told ABC News Australia that he would be interested in joining the effort. He said volcanic rocks recovered from the site would provide strong evidence for the existence of a volcano there.
The Limestone Coast already contains relatively young volcanic features, including Mount Gambier and Mount Schank, which erupted about 5,000 years ago. Mr Lewis said the volcanic field extends into western Victoria and appears to become younger farther west, potentially placing Beachport along the same pattern.
Any expedition would require extensive preparation and favourable conditions. Mr Lewis said low swell and northerly winds would be needed to make the seas safer, meaning a dive may not take place until late summer or autumn in a future year.