ABC News (AU)
· collected 2026-09-16 · by Josh Brine and Narelle Graham
Ian Lewis, a hydrogeologist from Mount Gambier, SA, proposes that unusual reefs discovered off the Limestone Coast in the 1960s during an oil and gas survey might be due to underwater volcanic activity. He plans to lead a dive expedition at these reefs, located about 20 kilometers offshore and at depths up to 45 meters, to collect samples for testing. The theory suggests that the largest earthquake in South Australia in 1897 may have been caused by an underwater eruption, which would make it the most recent volcanic event in Australia if proven true.
Written by the local model on 2026-09-17,
using this article's own text rather than the other coverage of the
same event (that is the story summary below).
In short:
An SA hydrogeologist has suggested unusual reefs off the Limestone Coast could be due to underwater volcanic activity.
uncertain
reefs → suggest → activity
The reefs were discovered in the 1960s during surveying for oil and gas reserves.
What's next?
asserted
What → discover → reserves
Ian Lewis wants to organise a dive at the site of the reefs to gather samples for testing.
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Lewis → want → testing
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.
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volcano → lie → 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.
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survey → say → coast
"One way to interpret them is: are they not limestone reefs at all?
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they → interpret → them
Is there some other rock?" he said.
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he → say → ?
"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?'
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reefs → put → 1897
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.
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he → say → 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.
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geologist → go → rock
"But I'm one of the few diving geologists, so it would be a real privilege to do it."
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it → 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.
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it → link → 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.
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which → include → Coast
Mr Lewis said the volcanoes of south-west Victoria and south-east SA generally became younger the further west they were.
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they → say → Victoria
"Roughly every 10,000 years or so it appears an eruption has occurred," he said.
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he → appear → ?
"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.
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Lewis → erupt → 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.
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we → think → 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.
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Richards → plan → mine
He said the prospect of finding an underwater volcano was exciting, and he would be keen to be involved.
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he → say → volcano
"If [the rocks] are [volcanic] then that's pretty conclusive proof that there's a volcano there," he said.
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he → be → ?
In the meantime, Mr Richards is organising his own expedition to explore limestone caves around Christmas Island.
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Richards → organise → 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.
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he → be → Beachport
Back on the Limestone Coast, Mr Lewis said any dive efforts off Beachport would require significant planning and ideal sea conditions.
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efforts → say → planning
"You'd hope for minimum swell, and northerly winds to flatten out the seas, which probably means late summer into autumn," he said.
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he → hope → autumn
"It may be a couple of summers away before we do this."
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we → do → this
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