Research suggests that eruptions are most likely to occur close to Colac, Port Fairy, Portland and Mt Gambier (pictured).
Credit: iStockPhoto
SYDNEY: While Australia's southeast is long overdue a volcanic eruption, its unlikely to be a major threat to life, Australian scientists say.
Western Victoria and southeastern South Australia have a history of playing host to small volcanoes. Over 400 small eruptions have occurred in the region in the past five million years, 20 within the last 40,000 years.
The last, at Mount Gambier, exploded some 5,000 years ago, making another eruption long overdue, said geologist Bernie Joyce from the University of Melbourne.
"Although the volcanoes in the region don't erupt on a regular sequence, the likelihood of an eruption is high given the average gap in the past has been 2,000 years," he said.
Dating the eruptions
To get a picture of how often the volcanoes would erupt, Joyce and colleagues catalogued and mapped the craters, lava flows and volcanic cones in the region to determine where the most recent eruptions took place. They then took and dated samples from as many of the volcanoes as possible, using argon-argon dating techniques.
Previous eruption dates were based on potassium-argon dating, which provided dates for the first four million years, but left a significant gap for the last one million years. "Now we have argon-argon dating which will give dates much younger, much nearer to the present," he said.
The researchers also used thermoluminescence and optically stimulated luminescence dating for the samples to fill in the gaps for eruptions in the past 20,000- 30,000 years. "We can now date where we had gaps before. For some volcanoes we have three or four (sometimes conflicting) dates."
Joyce presented his research at XXV International Congress of Geodesy and Geophysics in Melbourne this week.
The next big one
Joyce said the next event is likely to be in the west of the region, where the younger volcanoes are. "We're quite certain that the whole volcanic province is not extinct, but dormant or likely to erupt again."
"If they happen close to Melbourne or Geelong it could be hugely devastating. It is more likely however, that eruptions would occur further west, closer to areas such as Colac, Port Fairy, Portland and Mt Gambier."
Fortunately, these aren't the types of eruptions that kill thousands of people, as they don't have the death-dealing characteristics of Merapi or Mount St Helens, commented volcanologist Richard Arculus from the Australian University in Canberra.
The style of eruption wouldn't be explosive enough to kill you unless you were right on top of it, he said. "You could be within a kilometre or two of it… and not be at risk of dying."
The next really big one
The Australian volcanoes are babies compared to the supervolcanoes, according to vulcanologist Stephen Self from the Office of Nuclear Material Safety and Safeguards, U.S. Nuclear Regulatory Commission. Self presented his research at the same conference the frequency of past big eruptions that have shaken our planet.
Super-eruptions occur every 10,000 to 100,000 years and, said Self, and the next could occur in a few thousand years or next week.
"Every now and again, Earth suffers from tremendous explosive volcanic eruptions, much bigger than those witnessed in modern times. Although the return period for such events is long, perhaps every 10,000 to 100,000 years depending on the size, it is statistically more likely that Earth will next experience a large super-eruption than a large meteorite impact."
The last super-eruption took place 74,000 years ago in Sumatra, when Toba produced 450 cubic kilometers of ash and lava.
Mount Gambier erupting
How typical that a Melbourne based explosion would be devastating, but one in a regional area would be of no consequence. Most of Mount Gambier township is within one or two kilometres of Mount Gambier! It is also our main water source, so it would be devastating for the entire township, even if you survive the explosion.
But not to worry, because Melbourne will be fine.