100 Dormant Volcanoes discovered between Melbourne and Mt Gambier in Australia

[Jones]

The discovery of 100 underground volcanoes in the outback is set to change Australians' understanding of the continent, new findings claim.

An international team, including scientists from the University of Adelaide and the University of Aberdeen, uncovered the volcanoes using advanced subsurface imaging technology to identify volcanic craters, lava flows and magma chambers in the Cooper-Eromanga basins in South Australia.

The volcanoes developed in the Jurassic period, between 180 and 160 million years ago, and have been buried beneath hundreds of metres of sedimentary rocks.

And it suggests that Australia was more volcanic than previously thought.

Simon Holford, Associate Professor at the University of Adelaide, explained that these volcanoes could just be the start.
"Our discovery raises the possibility that there might be more buried volcanic landscapes beneath the surface of the Australian continent," Professor Holford told 9News.

Professor Holford also said the findings are significant because it provides a clearer picture of how the continent evolved.

"A great challenge when it comes to reconstructing the geological evolution of Australia is that much of the continent is covered by regolith which covers the underlying solid rock. Using approaches borrowed from oil and gas exploration, we've been able to peer below the cover of regolith and help add a few pieces to the puzzle of the evolution of the Australian continent," Professor Holford said.

"Also, active volcanic landscapes are often quite difficult to study – our buried volcanic landscape allows us to study a 'frozen' volcanic environment in a safer manner."

The Cooper-Eromanga Basins are now a dry and barren landscape, but in Jurassic times they would have been riddled with craters and fissures, which spewed hot ash and lava into the air, and were surrounded by networks of river channels, which evolved into large lakes and coal-swamps.

The research also suggests there was more volcanic activity in Australia during the Jurassic period than previously thought and could change the understanding of the processes that operated in the earth's past.

The researchers have named their discovery the Warnie Volcanic Province after one of the drill holes that penetrated Jurassic volcanic rocks (Warnie East-1), but also in recognition of the explosive talent of former Australian cricketer Shane Warne.

So, 100 volcanoes have been discovered in the Aussie outback

www.9news.com.au

 

[Laura]

So, one wonders if any of them might become active again, or has the continent moved beyond the sub-surface hot spots?

 

[Jones]

There's come indication that an eruption in the area is possible, but nobody seems sure about how probable it is. The following is comparing and contrasting the area to Kilauea, some points indicate that an eruption in this area could be more dangerous, but others indicate maybe not. Apparently this Australian field of volcanoes last erupted about 5000 years ago, but has experienced up to 10 eruptions in the last 10,000 years:

Spectacular images of recent volcanic eruptions in Hawaii are a little disheartening – especially given news reports suggesting there is a sleeping volcano under Melbourne that could awaken and erupt at any moment.

Understanding the geological differences between Melbourne and Hawaii is really helpful in working out how we can keep an eye on future risks in Australia.

The Newer Volcanics Province
Victoria and South Australia do host an active volcanic field, called the Newer Volcanics Province (NVP). This is not a single volcano with a large single chamber of molten rock (magma) — the common image of a volcano — but a widespread field of multiple small volcanoes, each with a small volume of magma.

Melbourne lies at the eastern end of the NVP, and the most recent eruptions in this area occurred over a million years ago.

Mt Gambier in southeastern South Australia represents the western margin of the volcanic field and the most recent eruption — only 5000 years ago.

Between Melbourne and Mt Gambier there are more than 400 small volcanoes that erupted over a period of 6 million years.

The NVP was most active between 4.5 million to 5000 years ago and volcanologists consider the field to still be “active” with the potential for future eruptions.

We do not know when the next eruption will take place.

Volcanoes of the Newer Volcanics Province (a) Mt Napier, SE of Hamilton (b) The Noorat complex (c) The Mt Gambier Volcanic Complex, near Mt Gambier (d) The Mt Schank Volcanic Complex, near Mt Gambier (e) Purrumbete volcano, near Camperdown (f ) Tower Hill volcano, near Warrnambool (g) The Red Rock Volcanic Complex, near Colac. Ray Cas and co authors

The NVP is located within a tectonic plate – and not along a plate edge like the Ring of Fire volcanoes (for example, Mt Agung on Bali).

Tectonic plates are large slabs of rock made up of the Earth’s crust and uppermost part of the mantle (the lithosphere) which form the outer shell of the Earth, and move around slowly relative to each other.

Volcanoes act in different ways
While Kilauea volcano in Hawaii is also located within a tectonic plate, it has several key differences with the NVP in Southeastern Australia.

Magma source and volume
While Hawaii sources large volumes of magma from deep within the Earth, the NVP only receives small amounts of magma from just below the Earth’s crust.

It’s worth noting here that the makeup of the magma is similar in both locations, with both erupting runny basalt – a type of rock low in silica, and high in iron and magnesium.

We suspect that in Australia’s NVP, magma can move very fast from its source to the surface (on a time scale of days). This can bring rock fragments of the mantle (xenoliths) to the surface as the magma moves too fast for them to melt.

Eruption frequency
Hawaiian volcanoes can erupt numerous times, but NVP volcanoes are largely monogenetic — that is, each only erupt once or over a restricted period of time.

Crust thickness
Hawaii is located on the oceanic crust of the Pacific Tectonic Plate, which is a thin (around 7 km) layer of material that is dense and rich in iron. The magma can rise through this crust quite easily.

In contrast, the NVP is located on continental crust which is much thicker (about 30km), richer in silica and much less dense. Magma finds it much harder to travel through this kind of material.

Water adds danger
The explosivity of a volcanic eruption can depend on availability of water.

“Dry” eruptions – where magma has little-to-no interaction with ground water or water on the Earth’s surface – typically produces mildly explosive eruptions such as lava fire fountains, showers of lava fragments and lava flows.

The most explosive, hazardous eruptions form where rising magma interacts with ground water, surface water or sea water. These “wet”, (phreatomagmatic) eruptions can produce deadly, fast moving, ground-hugging currents of gas and volcanic material – called pyroclastic surges, and send abundant fine volcanic ash into the atmosphere.

The Australian Mt Gambier eruption 5000 years ago was a “wet” eruption, and had a volcanic explosivity index of 4 on a scale of 0-8 (where 0 represents a lava eruption, 1 a spectacular lava “fire” fountain as recently witnessed in Hawaii, and 8 represents a catastrophic explosive super-eruption).

The accompanying ash column is estimated to have reached 5km to 10km into the atmosphere.

On Hawaii explosive eruptions are rarer because the magma has a low gas content and groundwater aquifers are not as large as in the NVP. However, when lava flows into the sea there are often phreatic or steam explosions which can be hazardous to nearby spectators.

There’s a lot we don’t know
Another important factor relates to how we keep an eye on volcano risk at the two sites. Kilauea on Hawaii is extremely well monitored, and tracking magma moving underground has helped predict eruptions.

In contrast, the NVP is less well monitored, likely because there is no present volcanic activity, and it’s a huge region.

However, warning signs of an eruption are likely to be similar in the NVP to those on Hawaii – small earthquakes, minor uplift and/or subsidence of the ground, changes in ground temperature and gas or steam rising out of the ground.

Also, based on present knowledge of the NVP, there is no clear eruption pattern we can use to try to predict when or where the next eruption will be.

If the NVP were to erupt, significant impacts on our lives would likely occur. These may include:

• the closure of surrounding roads by lava flows and ash fallout
• volcanic ash and rocks loading roofs of local buildings
• contamination of water reservoirs by ash
• damage to machinery and electricity infrastructure by infiltrating ash
• respiratory problems for people prone to asthma, and
• disruption to air traffic across southeastern Australia due to drifting ash clouds driven by prevailing south-westerly winds.

Further scientific research is required on active volcanic fields such as the NVP to know how fast magma travels from its source to the surface, how much warning we might have before an eruption, and how long an eruption and its impacts might last.

There’s a volcanic system slumbering beneath Melbourne

There's a dormant volcano sleeping under Melbourne - and it could erupt at any moment.

www.sbs.com.au

 

[Jones]

Another article:

“The magma here – molten rock from beneath the Earth’s crust – has a lot of gas in it and it erupts explosively,” says Julie, tossing a handful of the resultant volcanic scoria into the air. “And in this one, the magma came up and it hit groundwater. Magma is about 1200˚C. Groundwater is less than 100˚C. When those two things touch, there’s a huge explosion. I wouldn’t have wanted to be around when this was erupting.”

Some indication that there could be a bit of volcanic activity yet to come in the area:

“We do know that from Ballarat to Geelong there’s an area where something’s going on down in the mantle. It’s not a liquid, but the edges of the mineral grains are melting a little,” she says. “We can’t say whether it will erupt again. It could just sit there and do nothing. All we can say is the whole province is volcanically active and the new one could literally be anywhere, but the most likely place will be between Ballarat and Geelong.” Julie has counted 437 volcanoes in the NVP, 23 of which she’s identified herself, starting by looking on Google Earth for anomalies that suggest mini maars or lava flows."

"MONASH PHD STUDENT Jackson van den Hove is focused on just one volcano. Standing above Lake Purrumbete near the rural town of Camperdown, he sweeps his arm out to indicate “a perfect specimen of a maar volcano”.

He’s spent hours on a boat here, taking measurements to determine why, at 2.8km across, this crater is one of the world’s largest, and what the knowledge can do for volcanic hazard mitigation.

“With a crater the size of Lake Purrumbete – which can fit the whole of Camperdown – we need to know how you’re likely to be affected by such a volcano,” Jackson says. “When a maar volcano goes off, it blows the ground apart, which makes them very dangerous…and it also produces a big ash cloud.”

Victoria has the same kind of hazards as Iceland, where the Eyjafjallajökull volcano erupted in 2010, grounding aeroplanes across Europe, he says. “The ash cloud affects plane travel, and you only need a very small amount of ash to collapse a roof. It’s best to understand what causes them.” Jackson, perhaps fortunately, has determined Purrumbete’s size isn’t down to just one massive eruption. He’s identified at least three and maybe five eruption points in the crater. These, and erosion, have broadened the lake considerably.

Equally illuminating is his discovery that the ground beneath Purrumbete is composed of “poorly consolidated sediments”, with the blasts resulting in a similar set-up to that which saw the ground under Christchurch, New Zealand, “turn to mud” when struck by the earthquake in 2011. Yet Jackson isn’t too concerned for the moment, adding that “the hazards for Victoria are not grievous”.

Forged by fire: Volcanoes in Victoria

There are hundreds of dormant volcanoes and other geological features smattered across Victoria's Western District.

www.australiangeographic.com.au

 

[Jones]

Here's some information on the hotspot in Australia - it's currently in the Bass Strait between Victoria and Tasmania:

Hotspot system in our backyard

We have a hotspot system of our very own. Australia's hotspot currently lies under Victoria, Bass Strait, Tasmania, and the floor of the Tasman Sea at a latitude of about 40°S. It's one of more than a hundred systems identified around the world. As far as hotspots go, the one in our backyard is slumbering. Present hotspot activity is possibly confined to the triggering of earthquakes in predicted areas, such as the recent event off the coast of north-west Tasmania, and deep gas discharges under Victoria and Tasmania.

Scientists believe a new Australian volcano is being created.

Geologists suspect an earthquake that originated 50 kilometres from King Island in February 2002 signalled the reawakening of the hot spot, a region in the Earth's crust where the planet expels some of its internal heat.
Australia's hot spot is several hundred kilometres wide and lies under Bass Strait and parts of Victoria and Tasmania.


Wally Johnson, a vulcanologist at Geosciences Australia, said the fact that there were earthquakes taking place in the area "means that geologically, the hot spot has to be regarded as active, even though it hasn't produced volcanic eruptions as such".
He said it could spawn a volcano within 100 years.

Romsey Australia: Volcanic eruption risk and maps

romseyaustralia.com