Geologist hopes to find evidence of underwater volcano

Australia's youngest volcano could lie off the coast of a South Australian fishing town, according to a theory being advanced by a prominent hydrogeologist.

Mount Gambier's Ian Lewis said geologists had long wondered if a volcano lay off the coast of Beachport, on the Limestone Coast, after an oil and gas survey from the 1960s revealed three irregular reefs running at right angles to the coast.

"One way to interpret them is: are they not limestone reefs at all? Is there some other rock?" he said.

"Geologists putting two and two together have said: 'Is it possible that the largest earthquake in South Australia [in 1897] may have been a sub-sea eruption, and the three reefs are lava flows?'

"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."

After many years of speculation, Mr Lewis said he hoped to take a team to dive at the location, about 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."

A volcano-rich area

If the theory linking the eruption of an underwater volcano to the 1897 earthquake were proven, it would be the most recent Australian volcanic eruption, excluding overseas territories.

But some of Australia's other young volcanoes, including Mount Gambier and Mount Schank, which erupted about 5,000 years ago, are also located on the Limestone Coast.

Mr Lewis said the volcanoes of south-west Victoria and south-east SA generally became younger the further west they were.

"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."

Another potential sign of what lies below the surface, Mr Lewis said, was 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,"

he said.

"Even if we got to there and trapped the gas in a container and tested, we might find out if it's volcanic gases, even before we do any diving."

Planning for an expedition

Diver Josh Richards has discovered cave extensions on the Limestone Coast, and took part in efforts to rescue people trapped in a Laos mine earlier this year.

He said the prospect of finding an underwater volcano was exciting, and he would be keen to be involved.

"If [the rocks] are [volcanic] then that's pretty conclusive proof that there's a volcano there," he said.

In the meantime, Mr Richards is organising his own expedition to explore limestone caves around Christmas Island.

"There are quite a few parallels between what Christmas Island has done, and what Ian is proposing has occurred offshore at Beachport," he said.

Back on the Limestone Coast, Mr Lewis said 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.