Forged by fire: Volcanoes in Victoria
ON A CLEAR but severe winter morning, when the wind cuts right through you, being atop Red Rock in south-western Victoria is still an impressive experience. Just to the west is Victoria’s largest inland body of water, Lake Corangamite, where the cold could almost have us believe the white swirls on the surface are snow drifts. Yet they’re salt, for this shallow lake is generally three times saltier than the ocean.
Just below us is a large green crater, pockmarked by dozens of smaller craters, as if a golf-course curator has let the fairway grass grow into the bunkers. Behind us are grapevines, bare after their harvest, in rich red soil, and surrounded by round low hills with nary a tree to blot their surface. What trees there are partially mask a substantial stone farmhouse, for this is the start of Victoria’s Western District, prized for its wool, dairy and wheat.
And everything we see from here and beyond to the South Australia border – the hills, the lakes, the fields, the walls that fence them and often the paving on the roads that run along them – is down to volcanoes. Many might be mere bumps on the horizon, but given the variety of the 400-plus volcanoes here, there are few other landscapes like it in the world. And it’s why British-born geologist Dr Julie Boyce came here to do her PhD in what she calls “the perfect natural laboratory”.
Mt Leura at Camperdown dominates the landscape, and from the top you can see a ring of other volcanoes stretching in a 270˚ arc to the north, east and south. (Image: Don Fuchs/Australian Geographic)
Volcanically, it’s very young, and so it’s called the Newer Volcanics Province (NVP). Julie is with us on the scoria-strewn hillside at Red Rock, 12km north of Colac, to explain how these volcanoes formed – and where the next ones might appear.
“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.”
Red Rock is a maar volcanic complex, and the mini-craters we see from the car-park lookout are about 40 eruption points. Yet its near neighbour, Mt Alvie, is different altogether – a scoria cone – while just to the north, Warrion Hill is another type again, a composite scoria cone with lava flows. All this variety in such a small area convinces geologists that the NVP as a whole is rather volatile.
Red rock craters. (Image: Don Fuchs/Australian Geographic)
“These are baby volcanoes so they’re not really considered big and fancy,” Julie says. “We have to study them because we could get a new eruption in the next 5000 years, and it’s important that we have a good idea of the kinds of eruptions we could expect.”
Julie has a slightly alarming tendency to talk about eruptions in the present tense, but, given what she believes is going on under the surface, it’s for good reason.
“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.
VIDEO: Exploring volcanic Victoria. (Credit: Don Fuchs/Australian Geographic)
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”.
Lake Gnotuk in southwestern Victoria is an example of a maar – a shallow crater formed by a volcanic eruption with little lava. (Image: Don Fuchs/Australian Geographic)
SIMILAR TO LAKE PURRUMBETE, Tower Hill near Warrnambool is up there on the world maar volcano scale for size and complexity, but geologists have had no trouble determining its eruption points, because a series of scoria cones sits in its vast crater lake. It was their age that kept scientists guessing until Dr John Sherwood, a now-retired Deakin University environmental scientist, had “an incredible piece of luck”.
Quarries are a geologist’s best friends, because they do all the hard work in exposing the rock layers for analysis. And when the manager of a quarry next to Tower Hill reported they’d reached the old land surface before the eruption, he’d unearthed the local geological equivalent of the Dead Sea Scrolls.
“To his amazement the vegetation was in a remarkable state of preservation,” says John, as he pulls from a cardboard box a large rock with small pieces of wood poking out from it. He believes the blanket of ash from the eruption was hot enough to kill the fungi and bacteria that would normally break down organic matter, but not hot enough to destroy the vegetation.
“Two pieces of wood gave us a radio-carbon date, in remarkable agreement, of about 33,000 years,” he says. That figure tallied with other testing methods used at Tower Hill.
That the quarry owner was interested enough to appreciate his find is no surprise, because everyone out on the NVP – farmers, park rangers, gem fossickers, gardeners – seems to be an amateur geologist. After I scale Mt Porndon near Pomborneit for a good vantage point, local farmers Mary and Eric Harrison tell me of the challenges of working ground peppered with volcanic rocks. But Eric says soil tests showed it to be perfect. “Anything we care to plant, it will grow. But you can’t plough it.”
Mt Napier, south of Hamilton, as seen from the summit of Mt Rouse at Penshurst. Between these two significant volcanoes, the spreading lava has created what locals call ‘stony rises’. (Image: Don Fuchs/Australian Geographic)
OVER AT DERRINALLUM the community is so emotionally connected to their local volcano that they bought it, and now they’re restoring it. Mt Elephant so dominates the landscape that it was known as the Swagman’s Lighthouse, a beacon for itinerant workers, and it’s truly mesmerising as I watch it emerge in the first light of day. A scoria cone with a prominent breach, it had been in private hands since colonisation, but when it came on the market in 2000 the community dug deep.
In league with conservation group Trust For Nature, they raised $200,000, says Lesley Brown, a Mt Elephant Community Management member. We are standing in the bowl of its crater after an energetic walk up from the information centre they’ve just finished building. “The feat of raising that money shows you how people felt about the mountain and how much they wanted to keep it in community ownership,” she says.
The next task has been to restore Mt Elephant to how it was before grazing, bushfires and rabbits stripped it of worthwhile vegetation. Using old photos, paintings and even the sketchbook of colonial artist Eugene von Guerard – who sat on the crater rim to draw – they have been planting trees.
“The community is happy with some tree planting but they don’t want to lose the view of the mount, the elephant shape,” Lesley says. “We get in a little bit of trouble every now and then over that.”
Recent scientific testing on Mt Elephant by Curtin University in WA has put its eruption date at about 550,000 years ago – which has knocked out the theory held by locals in Derrinallum that it was only 20,000 years old. But more intriguing is the Aboriginal dreaming story of its creation. That tale has two spirits – the local from Djerrinallum (Mt Elephant) and one from Ballarat, 70km to the north-east, called Buninyong – fighting over a stone axe. Both mortally wounded, they returned to their own country to die, and the respective mountains are their bodies.
“We are not qualified to interpret these legends,” says Chris Lang, a local farmer and Mt Elephant conservation group member. “We used to believe that the legend explained why the mountains are where they are, their eruption and their shape. However, it is just as likely to illustrate where is the centre and the border of their people’s territory.”
Mt Elephant, a 240m conical breached scoria cone, formed by a dormant volcano, near the town of Derrinallum in south-western Victoria. (Image: Don Fuchs/Australian Geographic)
THE LEGEND ASSOCIATED with Mt Eccles, which the Gunditjmara people know as Budj Bim, isn’t violent, but the reality of settlement is, and indigenous guide Tyson Lovett-Murray credits the volcanic nature of the land with saving his people.
Tyson has a very straight way of telling a story. Sitting in the picnic ground at Mt Eccles National Park, 43km north-east of Portland, he recounts the Convincing Ground Massacre of 1834–35, when up to 200 Aboriginal people, asserting their right to take as food a whale washed up on a beach, were “rounded up” and shot. That sparked the Eumeralla Wars, which lasted 15 years and saw, Tyson says, the Gunditjmara fight a guerilla campaign.
“The Gunditjmara hunting grounds were disturbed when the sheep and cattle came in, and they spread out the kangaroos, which meant the Gunditjmara then had to take sheep and cattle… Gunditjmara used to leave the stony rises, grab 100–200 sheep and hunt them back into the stony rises for the meat. In most other parts of Australia, the ‘settlers’ would follow and let loose with their guns to teach them a lesson, but here they couldn’t ride horses onto that volcanic landscape,” says Tyson, who believes it was the rock that saved his people during the Eumeralla Wars.
Mt Eccles is only one of three landscapes in Victoria on the National Heritage List, and since 2007 it has been jointly run by Parks Victoria and the Gunditj Mirring Traditional Owners Aboriginal Corporation. The area has a vast variety of volcanic wonders – a crater lake, lava tunnels, an extensive lava canal – and a striking feature is the Natural Bridge, which is rare in the NVP.
Park ranger Peter Hill at the entrance to a lava cave at Mt Eccles, which is the source of a lava flow that extends 50km to the coast. (Image: Don Fuchs/Australian Geographic)
Basalt can flow a long way because it cools and crusts over on the top where it’s in contact with the air, and on the bottom where it’s in contact with the ground, leaving the middle insulated and able to flow. Eventually the eruption at Mt Ecccles ran out of magma and the levels of lava in the tube drained to form the open-ended cave. “It’s like a cathedral in here,” says Peter Hill from Parks Victoria. “The reason Mt Eccles was declared a national park was to protect these geological formations.”
The rocky floor is covered with lichen, and ferns hang down from above – but it’s the prevalence of moth wings that catches my eye. Bats eat the moths but discard their wings, and this double-ended cave is an ideal ambush site, because the walls aid the bats’ echolocation method of navigation.
About 80km away at Mortlake, Mt Shadwell has lost a fair chunk of its scoria cone. But not for much longer, because the quarry that has been digging away here for nearly 100 years is getting too close to the water table. So in about five years, says supervisor Keith Hargreaves, “We’ll close off, re-grass it, plant native trees, put a few rocks or features around for the lizards and snakes and we’ll hand it back to nature.”
Hopefully, fossickers will get as good a go in the new quarry. The current site contains Australia’s largest deposits of gem-quality peridot, a semi-precious stone with colours that range from dark green to a lustrous gold. Peridot comes from olivine bombs, which are part of the Earth’s mantle that has been ripped out and brought to the surface in an eruption. Keith’s team makes a stockpile of the larger rocks that don’t fit through their screens, and on Fridays, Saturdays and Sundays the public is welcome to rummage.
“If someone can find a commercial stone or give it to their girlfriend, daughter or wife, good luck to them,” Keith says. “I can guarantee everyone will find olivine, but I can’t guarantee everyone will find peridot.”
Blue Lake at Mt Gambier, South Australia. (Image: Don Fuchs/Australian Geographic)
ACROSS AT MOUNT GAMBIER in South Australia, the Blue Lake and its three companion maar craters sit in a precinct of groomed grounds, tracks and lookouts. They’re probably the NVP’s most visited volcanoes. To the city, though, the Blue Lake is its water source, derived from an eruption 5000 years ago, which formed a crater that quickly filled with groundwater. It is, Saad Mustafa confirms, an eye into the aquifer. And what an aquifer. Saad, a state government hydrogeologist, says the depth of the lake – about 70m – means a high degree of stratification in the walls, and on sunny summer days its dull grey turns a brilliant turquoise. “There is no other lake like this in Australia,” Saad says.
There’s been no other trip like this for me. Driving back through Port Fairy, photographer Don Fuchs senses that the late- afternoon light is ideal to shoot the lighthouse on Griffiths Island. The slippery black rocks on which he secures his tripod are from the eruption of Victoria’s largest and most complex volcano, Mt Rouse at Penshurst. That’s 56km away, and the river of rock we stand on may well extend even further into the ocean. Like this tour of the Newer Volcanics Province, that’s some journey.
This article was originally published in the March-April issue of Australian Geographic (AG#137).