When a nanny descends from the sky hanging from an umbrella, you know Mary Poppins has arrived. It may be the second best movie to watch at Christmas. (The most popular one remains the Muppet Christmas Carol.) Mary Poppins comes to take care of the children but ends up changing the grown-ups more. Even the most dour of bankers learns from her to laugh at the world. Fun explodes like a rhyolitic volcano. The most memorable bit of the movie (apart from some highly dubious accents) can be summed up in one word: “supercalifragilisticexpialidocious”. It means whatever it needs to mean. The word is much older than the movie. When first invented around 1930, it was a complicated way to say ‘splendid’. Later it was listed as having no meaning, apart from being the longest word in the English language. (In fact, it is the 5th longest.) In Mary Poppins, it is used as something to say when you have nothing to say. (Useful for Twitter, but you might run into the character limit for saying nothing.) It rhymes with ‘atrocious’, as used in an infamous UK headline when a major football team (Celtic) was beaten by some minnows from the Highlands, a merger between Caley and Thistle. “Super Caley Go Ballistic, Celtic are Atrocious!” wrote the Scottish Sun. (Yes, that newspaper title may be a contradiction in terms.) Mary Poppins turned not only the people upside down, but also the language.
What makes a good Christmas movie? Perhaps it is the same thing that makes a good Christmas: a family coming together. For just one day we can forget about the pressures of normal life, the need to be best or at least first, and enjoy each other as a company of equals. At heart, we are all socialists: whether democrat or republican, tory or labour, left or right, we need others around us, talking, doing, living together. This is the one day of the year we can enjoy the happiness of just being at home with others. This is the ultimate socialism, the original meaning of the term. It is the one day of Mary Poppins.
Let’s turn the world upside down and look at volcanoes that way. This is about the living volcanoes of the oldest of continents: Australia, and about the stories that were told over countless generations of family gatherings.
It is a few hours drive west of Melbourne if using the main road. Don’t. The spectacular coastal route, known as the Great Ocean Road, takes rather longer but is far more fun. While we meandered along it, the views alternated between the sea and the land. The winter landscape (it was August) was green, with patches of tall, dripping rain forest amidst the farming, mixed with the cliffs and waves at the coast. It didn’t look like Australia should.
After an in-land detour and a tree-top walk in the forest, we arrived back at the coast. Spectacular, steep limestone cliffs were fighting off the waves from Antarctica. A viewing platform showed us a number of tall but fragile looking rock stacks, called the Twelve Apostles. One of the stacks was missing: it collapsed a number of years ago leaving only 8. (If this seems to call into question Australian mathematics, the Twelve Apostles is a name, not a number.) As darkness fell, most of the other tourists went back to the small car park. They left too quickly. In the growing winter darkness, brown shapes emerged from the sea below and waggled their way up the beach. They were little penguins which live here year-round. We watched them until it became too dark to even see the beach and waggled our own way back to the car.
The Apostle rock stacks were formed by coastal erosion. They are where the coast used to be but was beaten back by the storms. The rocks and coast are limestone, easily eroded by the Antarctic waves. The limestone is grey, in effect carbonate sand. It was deposited in an ocean some 100 meters deep, between 14.5 and 10.5 million years ago. It started during the Miocene climate optimum (yes, that is a name) and continued while the climate had begun to slowly cool and ice grew in Antarctica. The limestone layer is up to 240 meters thick. It includes some pollution from volcanic material which was slowly becoming more felsic over time. Volcanoes were at large, somewhere to the east.
Above the limestone is a layer of clay, the Hesse Clay, and a layer of sand, the Henson Plain Sand. They show that the area was changing. The land was rising as new mountains were building to the north. The shelf where the limestone had formed was now approaching sea level and 5 million years ago, became land. Rivers build up a fluvial plain of sand. Temperate rain forests started to grow. The clay and sand contain volcanic ejecta, in proper Christmas fashion fallen from the sky.
But nothing volcanic was visible from our viewing platform. The little penguins spend the night undisturbed on the beach – they came on-land for safety, not for eruptive entertainment.
Driving back we took the in-land road. The vegetation changed: the green, undulating landscape looked quintessential English, seemingly far too fertile for Australia. The cloudy weather also looked like England. We passed towns and lakes. On the edge of the town of Camperdown a green, steep, cone-shaped hill appeared. A narrow road took us to the top, through the small open forest on the slopes. The summit formed a semi-circular ridge half surrounding a deep depression. The hill, called Mount Leura, was clearly volcanic in shape. It is in fact a 130-meter-high scoria cone with a large central crater. Part of it is (optimistically) called Sugarloaf Mountain. The view showed small bumps surrounding the peak. In the distance were other cones, in seemingly random directions. A small display provided their names: Mount Shadwell, Mount Ewan, Lavers Hill. This land was littered with volcanic remnants, eruptions of yesteryear.
Mount Leura erupted only once, 160,000 years ago. It was an eruption in phases, which moved around a bit. After the cone had build, an explosion formed the crater and breached the cone in the process. More, small peaks formed around it, partly merging into a volcanic complex. And then everything ceased. The mountain had been quiet ever since. A long time after, people arrived, build their camp on the edge of the hill, and told stories about how this solitary mountain came to be, and about the spirit hiding within it.
The scattered cones give the impression of isolated eruptions. In fact, these eruptions here were far larger than the cones that they left behind suggest. Look beneath the surface, and signs of lava are everywhere. A basaltic volcanic province appears. It may not be a proper flood basalt, but it certainly is a member of that family. It has a story to tell.
Newer Volcanics Province
Australia has far more volcanoes than it gets credit for. Many are found near the east coast. The youngest ones are in the Northwest Territories and here in Victoria on the south coast of Australia, both with possible eruptions in the last 10,000 years.
The young volcanic region in Victoria we had traveled through on that winter day is called the Newer Volcanics Province. (In Australia, anything younger than a few million years counts as ‘new’.) It extends westward from Melbourne to Mount Burr, a distance of 400 kilometers and covers an area of 23,000 km2. Australia doesn’t do small! The landscape is smoothly undulating farmland interspersed with lakes (of all sizes) and stony ridges. Isolated steep hills suddenly rise from the farmland, looking like someone dumped them there. They, of course, are volcanic. But so is the farmland.
The entire region is covered with basaltic lava flows, top to bottom. The hills or cones are just the tip of the iceberg, the acne of a volcanic surface. The farmland appears smoothly undulating because the lava flows have filled in the original valleys. Some of the lava is ancient and fully weathered. Other flows are younger and still rough, forming stony ridges in the landscape that can be difficult to cross. In places, thin scoria layers have been dumped on the land.
It is called an ‘intraplate continental basaltic volcanic province’. These are not uncommon: every continent has them. They tend to be long lasting, lack central volcanoes but instead have many different eruption sites each of which is short lived. Each province can have hundreds of such volcanoes. Eruptions occur infrequently, thousands of years apart (or more) but they can pop up anywhere within the province and at any time. The eruptions form large lava flows, scoria cones, maars, tuff rings and volcanic complexes.
The Newer Volcanics Province has 416 known eruption centres with 785 known eruption sites: about half the eruption centres are ’complex’, meaning that they erupted from more than one location.
The individual cones can be hard to date. They are deeply weathered – even Australia has weather! But some cones appear recent, pleistocenic, perhaps even holocenic. In fact, five eruptions have been dated to within the past 100,000 years and 2 to within 10,000 years. The youngest are around 5,000 years ago.
The eruptions began 4.5 million years ago, during the pliocene. There was an earlier phase of volcanism 7-6 million years ago but that seems not directly related to the Newer Volcanics Province: they included felsic magmas while the later volcanoes were exclusively basaltic. The Newer Volcanic Province likely started north of Melbourne and over 4.5 million years slowly extended westward. The oldest eruptions were more often inland, especially towards the northeast. The youngest are often nearer the coast, especially in the far west of the region. But in reality volcanoes of any age can be found anywhere. The maars are mainly in the southern part, where the rising magma had to pass aquifers. Just south of them there is a sharp cut-off: no volcanoes exist south of this line.
The volcanoes tend to cluster around known fault lines. These may provide convenient paths for magma transport from depth.
There are too many to list. The highest scoria cone is Mount Elephant with a height of 240 m. Mount Rouse, 285,000 years old, is the largest by volume. Its double scoria cone is about 100 meter high and is breached on one side. Two craters are located just outside the cone. Eight eruption points have been identified. The eruption here produced lava flows that reached Port Fairy – 60 km away! Lava tubes were needed to carry the lava over such a large distance. The lava covers an area of 450 km2. The total volume is in excess of 1km3. This combination of lava and scoria is common for the area.
Red Rock is an example of another type of eruption. This complex includes both maars and scoria cones, covered an area of 7 km2 and includes at least 40 different eruption sites. It formed on top of an older lava flow. There are nine lakes which formed in at least 18 separate explosions. These maars formed in an early phreatomagmatic phase. The 22 scoria vents mostly formed later, when lava could reach the surface unimpeded by water. Red Rock is the most complex of the known volcanic sites of the Newer Volcanic Province. It is surprising to see scoria cones, maars and a lava shield all from the same eruption and within 1 km of each other.
The Mount Gambier volcano (not to be confused with the town of the same name, situated on its edge) consists of a cone with a large crater, and a separate maar called the Blue Lake. The colour is seasonal: in winter the lake goes grey but in summer it indeed becomes a dazzling blue. The main eruption has been modeled as an explosive VEI 4, at 0.3 km3. The explosion occurred when the rising magma met the ground water: it ejected a cloud 5-10 km high and closed the airspace over Melbourne for days. Not that that mattered as neither airplanes nor Melbourne existed at the time.
(Whether Father Christmas would be affected by the airspace closure is not yet known. Studies are ongoing to measure the effect of airborne ash and sulphate on flying reindeer.)
Australia has been occupied for a very long time, and by the same people. The oldest evidence for human presence in the Northwestern territories is dated to 65,000 years ago. Southeast Australia was reached 40,000 years ago. Unlike the rest of the world, it seems there was a remarkable continuity, with the same groups remaining in one region for the entire period, each with different cultures and languages. Once settled, they did not easily migrate. Any people who remained this long must have been very well adapted to their environment. Knowledge was passed on effectively between the generations. This was done through the oral tradition called the ‘Dreaming’ which included stories, traditions and practical knowledge. Any unusual event was retold and remembered. Over 10,000 years or more, rare events will return: a long memory helps to know how to survive them. The recollections and advice needs to survive far longer than living memory. “For when you dream, you’ll find all that’s lost, is found.” – Mary Poppins.
Direct evidence that humans were present during eruptions is sparse. A post hole that was was sunk near Tower Hill serendipitously uncovered a stone axe, buried 1 meter deep below a layer of stratified tuff. It is now called the ‘Bushfield axe’, and proves that humans were in the area before or during the eruption. The ejecta have been dated using radioactive decay to between 34,000 and 40,000 years ago. A large lava flow from a hill 40 km away, Budj Bim (Mount Eccles), was dated to approximately the same time. There have been no other eruptions in the region since. Human presence (and their axe) goes back a long time here.
Indirect evidence for human presence during eruptions comes from Aboriginal stories passed on through the Dreaming. There is a term for it: Geomythology. Robert Smyth, in the 19th century, reported that “The [Aboriginal Australians] point to some of the recently extinct volcanoes, and say that fire came from them once.” He also wrote that the Aboriginal Australians used the term Willum-a-weenth for these hills which once had smoke and steam. ‘Willum’ can be translated as dwelling place, and ‘weenth’ is a word for fire.
Stories exist about Mount Leura too. A 19th century report states that “when some of the volcanic bombs found among the scoria at the foot of Mount Leura were shown to an intelligent Colac native, he said they were like stones which the forefathers told them had been thrown out of the hill by the action of fire.” This mountain last erupted 100,000 years, long before Aboriginal Australians arrived in the area. The association of such stones with fire came from other mountains.
There is a word ‘kulur’ which is widely used for places across the volcanic plains. The word means ‘very hot’ or ‘burning’. It is sometimes translated as ‘lava’. The word is attached to places such as Mount Sugarloaf which was known as Kulorr-Kulorr (‘lava stone’), and Mount Rouse. These mountains have not erupted in the Aboriginal Australian era but the type of stone was apparently known to come from fire, just like we can recognize solidified, stone-cold rock as lava. The Stony Rises, old lava flows, were known as ‘Kurt baulen’ or ‘stone islands’ and as Kullorr maleen meaning ‘lava islands’.
Aboriginal stories tell about mountains throwing stones at each other. The mountains that are involved change: a similar story is told about several different ones. In one version, it relates to Mount Buninyong and Mount Elephant throwing stones at each other ‘in a fiery wrath’. Another version has Mount Franklin throwing stones at Mount Tarrengower. (The latter is not volcanic.) If there is an event behind these traditions, it has become attached to the wrong mountains as none of these have erupted within the past 100,000 years. The stories are always about local mountains, and explain how the landscape around them came to be.
But which eruptions could be at the origin of the stories? Only four are known within the Aboriginal Australian era: Mount Gambier, Mount Schank, Tower Hill and Budj Bim. The first two form a pair, located in the same (western) region and erupting within 1000 years or so, possibly simultaneous. The last two are further apart, but are both in the central region.
The Aboriginal name for Tower Hill was Koroit, meaning ‘place of fire’ or ‘smoking, hot ground’. (Different sources do not always agree on the precise translation of the many Aboriginal languages!) There were several reports in the 19th and early 20th century that the local Aboriginal Australians talked about this quiet mountain once emitting fire, ashes and streams of molten stone. According to their tradition, their ancestors had seen burning mountains there. Budj Bim shows up in the earliest stories, about the creation of their world. In those stories, the low hill of Budj Bim represents one of the four ancestral beings; lava spat out as it burst through the ground. They also refer to the “land and trees dancing”.
Did they really pass on memories of an eruption that happen 37,000 years ago? It would be by far the oldest story in existence among any human population! The Bushfield axe shows that there were people in the Tower Hill area at the time. Who they were, and whether they were the ancestors of the later population is something we can only guess at. Extreme cultural continuity would still be required, with the people continuing with their way if living while the world outside went through the depth of the ice age and the holocene after this, and spread around the globe. When the eruption occurred, all of America was still Terra Incognito. Oral traditions can survive for a long time, even in our transient western culture. Our fairy tales paint a strange world where witches have power, forests are dangerous and wolves are a threat. Those tales are older even than our language and have migrated with our ancestors across Europe. Rumpelstilskin may be 4,000 years old and Jack and the Beanstalk 5,000 years. Different versions of the latter show that the latter predates the east-west split in the Indo-European language. Perhaps a culture as stable as the Aboriginal Australians could hand down their stories ten times longer than the rest of us. Further north, in Queensland, Aboriginal stories recall changes to the landscape that we now know happened more than 7,000 years ago. It is possible. “Let the past take a bow. The forever is now.” said Mary Poppins.
But the memories may not necessarily have been from Tower Hill and Budj Bim. The stories about mountains throwing stones at each other clearly became attached to different mountains – people had forgotten the actual locations. Names change and this can confuse the stories, or people move to a different area and the story has to move with. (People have even searched for Noah’s ark on Mount Ararat, not knowing that Ararat referred to a different region in those days.) The stories about an erupting mountain came without a clear description of which mountain. When people saw signs of past eruptions around a mountain in their region, which fitted the descriptions, it was tempting to associate the stories with that mountain. The jury is out: the memory may not be quite as old as the mountains.
But that still means that some eruption must once have been witnessed, to provide an origin for the stories. That brings us to the two youngest eruptions, Mount Gambier and Mount Schank, located on the western end of the Newer Volcanics Province.
There are two stories which relate to it. One comes from the region near Portland which is 80 kilometers to the southeast from Gambier. Aboriginal stories in this region recalled a tsunami: long ago a great wave came to Portland, destroyed an isthmus, overran the beach and devastated the land and forest beyond. A large tribe was almost wiped out and only a few members survived to tell the tale. The story says that ‘when Mount Gambier begins to burn, and the earth to shake, the tidal wave will come again’. Tsunamis on the Victoria coast are very rare. Tsunamis from earthquakes in the Pacific (Tonga, Indonesia, Chile) don’t normally reach beyond New South Wales. In the story, the tsunami was specifically associated with Mount Gambier. But Mount Gambier is 15 km from the sea. Mount Schank is located between it and the sea and is perhaps more likely to have caused a tsunami but even it seems rather far to move the sea. There is another possibility. In this area, the steep edge of the continental shelf is very close to the coast, with a deep basin beyond. An earthquake could cause a large slide on this edge, and thus trigger a tsunami. Earthquakes are uncommon in the New Volcanic Province, but there have been a few small ones south of Mount Gambier, at the edge of the continental shelf. And the story did associate the eruption with ‘shaking’, suggesting a large earthquake.
The second story is much harder to interpret. It tells of Craitbul and his family, who lived on Mount Muirhead where they would collect roots and roast them in ovens underground. One night they were woken by the shriek of a ‘bullin’ bird. The family fled to Mount Schank, but one night the same happened there. So they fled to Mount Gambier and lived in peace for a long time. But one day water came up in their oven and put out the fire. This happened four times, in four different ovens. The story mentions that they fled from an evil spirit called ‘tenneteona’, a word similar to the local word for lava.
The story is interpreted in different ways. The ‘ovens’ may be the volcanic craters. The maar craters around Mount Gambier do indeed periodically fill with water. But what is the ‘bullin’ bird? Suggestions include the noise of boiling water, or fumaroles. The spirit they fled from could have been the ground becoming too hot. Mount Muirhead has not erupted for more than a million years and may be a case of mistaken identity in the story. Does the remainder talk about the eruption of Mount Schank 5,000 years ago, and was there an eruption from Mount Gambier afterwards? It is far from obvious. The story says that tenneteona appeared not to exist far from the coast which is why the family moved to Mount Gambier.
Mary Poppins would have taken us into the story and show what really went on – with song and play. Her guidance is badly needed. We can take the story as a warning about the dangers of those mountains and their craters. The association of lava with proximity to the coast may represent a true recollection: three of the four holocene eruptions have been close to the coast. But this story is unclear. The previous story was far more direct about Mount Gambier having erupted a long time ago.
The stories indicate that the people knew about eruptions and could recognize rocks and features that were caused by eruptions, by explosions and lava. This is not unique to Victoria. Queensland has had eruptions 7,000 years ago, and the Aboriginal Australians there recall the lava, the ash clouds, and small phreatic explosions. They mention later steam clouds, terrible to see but not dangerous. The traditions focus on smoke, fire and heat and sound. Myth is not about memory. It is about experience.
In our fast-changing world, we forget how powerful words can be. The stories we tell at the family time may be passed on over generations. Whilst tweets are fleeting, stories can last forever. It is sobering to think that the Aboriginal Australian’s memories may have been passed on for more than 1000 generations, ten times longer than the oldest memories in our bible. “Everything is possible” says Mary Poppins.
But that ancient link is now broken. Many of the traditions and stories became at risk when the Aboriginal Australians were banned from speaking their own languages and their families were broken up. Cultural continuity ceased and invaluable information about the past was lost. The stories above were mostly reported in the 19th century, before the cultural vandalism. Those reports, and one stone axe, are all that remains. It is a massive loss not just for science, but for humanity.
There are stories behind the stories. Science too is a form of Dreamtime. It poses questions, searches for answers and tells the results for future guidance. (Future use is harder if the research is published behind a paywall!) “Enjoy the adventure. Don’t spoil it with questions” said Mary Poppins. She may have been practically perfect, but she was wrong on this one.
The cause of an intraplate volcanic province can be difficult to determine. The obvious explanation of a hotspot trail doesn’t work. The Newer Volcanic Province shows no age sequence, and the westward extension over time is not in the direction of plate motion. It seems that its volcanism is not tied to a location in the deep mantle. We have to look elsewhere.
One idea is that is the fault of Antarctica. When Australia split off from Antarctica, the thinning of the crust and rifting allowed warmer material from the upper mantle to rise up. A somewhat similar idea is that Australia is moving so fast (7 cm per year) that the lithosphere can’t keep up. The different speeds set up convection, where the lower lithosphere finds itself falling behind and rises up behind the steep edge of the thick continent. This edge convection sets up a warm layer which is following Australia.
What these ideas have in common is that they apply only to Australia. Intraplate continental basaltic provinces occur on all continents including Antarctica. It would be nice to have a more common explanation. We are still searching: the cause of these provinces remains in question. Maybe Mary Poppins did have a point. What the provinces have in common is that volcanism is very long-lived, intermittent, widely dispersed but remaining within the same large area of the continent, where the magma composition can change over time or differ per location. The volcanoes are monogenetic, meaning that after an eruption episode the conduit has time to fully solidify and closes for further business. The volcanoes probably erupt for days to months, rarely longer. The individual lava flows are mostly small and thin, certainly compared to flood basalts, but can also extend 50km or more. They are the most abundant type of volcanoes on Earth and yet remain the least understood!
The Newer Volcanic Province is probably the largest one currently in existence. The volcanic field extends slightly off the coast with evidence for some submarine eruptions. The Province has been going on for a long time: at one location, 28 lava flows have found on top of each other, one per 100,000 years or so. The oldest data lava in deep cores is 4.5 million years old. The landscape has been completely changed by the volcanic activity. Some of the numerous lakes are maars, while others formed when rivers were dammed by the lava flows. Valleys have been filled in by lava and ejecta.
Some of the maars are very large, up to 3 km. However, it appears that this does not reflect the explosion size. Instead each were formed by a number of smaller explosions which enlarged the crater. Typical eruption sizes for each volcano are VEI 3 to 4. Mount Leura is around 0.3 km3, as is Mount Gambier.
The amount of lava that is produced is highly variable. Both Mount Schank and Mount Gambier produced little lava, but instead had much more violent explosions which covered the area in extensive air-fall tephra.
The location of the individual volcanoes seems to relate to nearby faults. For instance, the vents of Mount Gambier are aligned with a nearby fault. These faults seem to allow the magma to migrate upward. The picture that emerges is that of a ‘leaky field’ where magma leaks upward over a wide area through any holes that become available, each volcano like the chimneys of Mary Poppins’ London. The type of eruption depends on details of the local environment of each chimney. “Anything can happen, if you let it” – Mary Poppins.
The relation to local faults can cause the eruptions to be along short fissures. This is evident in Mount Schank. It’s eruption appears to have started with fountaining along a 3.5-km fissure, followed by the maar-forming explosion to the south.
Evidence for an origin in the upper mantle comes from xenoliths: mantle inclusions in the lava, sometimes several centimeters across. Magma from Mount Rouse was found to have come from a depth of around 55 km, at the base of the lithosphere; it had collected there in small pockets. At least three separate batches with different compositions contributed to its eruption. It sounds a little like the Reykjanes peninsula.
The question remains, why is the Newer Volcanic Province here and why is it here now? If it is caused by the location at the trailing edge of Australia, why did it only develop in the past 5 million years? Why the sharp southern boundary along the Colac Lineament? And where does the mantle warmth come from? None of the earlier suggestions seems to explain all these features: hot spots don’t work and edge convection works much too well.
It has been suggested that the true driving force is tectonic: the stress that the movement of New Zealand is putting on Southeast Australia across the distance, perhaps transferred via the Tasmania fracture. This would explain the location and stability of the Newer Volcanic Province. A separate explanation would still be needed for the warmth in the region. Edge-driven convection might do that. Large events such as volcanic provinces may need more than one cause to come together. They are geological accidents, or for volcano hobbyists, Christmas come early.
But perhaps we should just enjoy the scenery. As Mary Poppins would say, “Why complicate things that are really quite simple?”
The next eruption
It is very unlikely that we will personally see another eruption here. The average time between eruptions is something like 15,000 years. However, if it did happen what would we see? What would we tell our children at the family Christmas gatherings, to impart the knowledge of what to do in future events? “What’s to happen all happened before” confirms Mary Poppins.
All eruptions have a lead-up time and a trigger. In the Newer Volcanics, the lead-up can be viewed as the growth of a magma pocket. The trigger is something which allows that pocket to migrate up. As faults are involved, a plausible event would be a tectonic earthquake. The growth of the magma reservoir may be imperceptible if it happens too slow and in a region ductile enough to avoid any earthquakes. For the trigger, movement on a fault would be an obvious choice, especially since most of the region is seismically quiet – at normal times. A larger earthquake would be followed by episodes of small swarms as the magma finds pathways. No conduit exists, so rock-breaking earthquakes follow as a dike feels its way towards the surface. Finally, possibly after a quiet phase, the eruption begins. It could happen anywhere in the province. The onset may be explosive if the location is above an aquifer. It may be a small fountaining fissure. A new cone grows but stops after a week or so. An adjacent location erupts, and now may produce lava that feels its way around for a way to the sea. The flow extends for kilometers, may be much more, but it doesn’t get to the coast. After a month or two the flow ceases. The process repeats a few more times in adjacent locations but every time it is less energetic than before. Finally the eruption ends, but the explosions do not: hydrothermal explosions continue in the area for some years. There is damage and destruction, of course, but unless the initial event is in a build-up area (for instance Camperdown) the impact is limited. Melbourne gets a two-day dusting with ash and the airspace over southern Australia is closed for a week or so. After that, the tourists flock in.
Where would it be? Anywhere, really – that is the nature of these provinces. They are unpredictable; past locations are no guarantee for future performance. Think of it as a Christmas present. Based on the more recent eruptions, a location within 20 kilometers of the coast seems more likely. But there is another area where geothermal heat maps suggest the presence of magma pockets: near the town of Bendigo, northwest of Melbourne. There is nothing that suggests an eruption is likely here. It is just one of many places to keep an eye on. We are a bit like the chubby little fellow with flying reindeer, looking for the right volcanic chimney.
It is all guess work, of course. Volcanism in the region is varied and unpredictable. There should be monitoring in the region, just in case a build-up is happening. It is plausible that magma is already lying in waiting underneath many locations, held back by a lack of earthquake triggers. This is, after all, a quiet, seismically sleepy region.
Any maybe that is the final secret of the Newer Province. It was always at risk of eruptions, but the Province only burst to life when something destabilized the crust and opened the faults. What really happened, 5 million years ago? That, I am told, is another story.
Albert, 25 December 2022
Erin L. Matchan et al. Early human occupation of southeastern Australia: New insights from 40Ar/39Ar dating of young volcanoes. Geology, 48, 390–394 (2020)
Benjamin Wilkie at al. Volcanism in Aboriginal Australian oral traditions: Ethnographic evidence from the Newer Volcanics Province. Journal of Volcanology and Geothermal Research, 403, 10699 (2020)
R. Cas et al. The dynamics of a very large intra-plate continental basaltic volcanic province, the Newer Volcanics Province, SE Australia, and implications for other provinces. Geological Society, London, Special Publications, 446, 123-172 (2016)
Julie Boyce et al. Variation in parental magmas of Mt Rouse, a complex polymagmatic monogenetic volcano in the basaltic intraplate Newer Volcanics Province, southeast Australia. Contrib Mineral Petrol, 169, 11 (2015)
From all of Us to all of You: VC wishes all you readers a Merry Christmas, and a Hunga Tonga 2023!
Some previous Christmas posts