Geologist Seeks Proof of Underwater Volcano off South Australian Coast

A prominent hydrogeologist believes that Australia's youngest volcano could be located off the coast of a South Australian fishing town. Ian Lewis, from Mount Gambier, has put forward a theory that a volcano may lie off the coast of Beachport, on the Limestone Coast.

Geologists have long been fascinated by three irregular reefs discovered in an oil and gas survey from the 1960s, which run at right angles to the coast. "One way to interpret them is: are they not limestone reefs at all? Is there some other rock?" Mr. Lewis said.

The reefs have sparked speculation that they could be lava flows from a sub-sea volcanic eruption, which may have been linked to the largest earthquake in South Australia in 1897. "Those of us who are geologists have been aware of this for a long time, but it's really been in the realm of dreamland," Mr. Lewis said.

Beachport is a popular tourist and fishing town, and Mr. Lewis hopes to lead a team on a dive at the site, approximately 20 kilometres off the coast and at depths of up to 45 metres, to collect samples for testing. "The idea of a geologist under the water in the middle of the ocean going tap, tap, tap on a rock is pretty bizarre," he said.

"But I'm one of the few diving geologists, so it would be a real privilege to do it," Mr. Lewis added. The Limestone Coast is home to several young volcanoes, including Mount Gambier and Mount Schank, which erupted around 5,000 years ago.

If the theory is proven, it would be the most recent Australian volcanic eruption, excluding overseas territories. Mr. Lewis noted that the volcanoes in south-west Victoria and south-east SA generally became younger the further west they were located. "Roughly every 10,000 years or so it appears an eruption has occurred," he said.

"If they're erupting progressively westward, Beachport would be in line as another spot," Mr. Lewis added. Another potential sign of what lies below the surface are anecdotal reports from fishers of small bubbles coming to the surface near the reefs.

"I don't think they're huge, just little streams of little pin-prick bubbles," Mr. Lewis said. Diver Josh Richards, who has experience with cave exploration and rescue efforts, is excited about the prospect of finding an underwater volcano and may be involved in the dive efforts.

"If [the rocks] are [volcanic], then that's pretty conclusive proof that there's a volcano there," Mr. Richards said. Planning for the expedition is underway, but Mr. Lewis said that any dive efforts off Beachport would require significant planning and ideal sea conditions.

"You'd hope for minimum swell, and northerly winds to flatten out the seas, which probably means late summer into autumn," he said. "It may be a couple of summers away before we do this," Mr. Lewis added.