The Best Australian Science Writing 2012 (14 page)

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It is around midday and Roger Wood is heading for the gate when somebody flags him down.

‘Morning, Roger!' says Steve Andrews, his neighbour, standing at the intersection of the two properties.

‘Morning, mate.' Roger wipes some of the sweat off his neck. ‘Hot enough for ya?'

‘Too bloody hot. What do you know about that, Rodge?'

What? He follows Steve's outstretched hand. A column of smoke has appeared in the northwestern sky behind him. He
raises an eyebrow: that was quick. It wasn't there when he drove down a few minutes ago. Looks a long way off, though.

He listens in to the police radio, learns that a fire has just broken out at Kilmore East. Does a quick mental calculation.

‘Should be right, Steve. Good – what? – 50ks away? Change oughta be here before it gets anywhere near us.' He leaves his neighbour standing there, but as he cruises up the mountain he feels a ripple of anxiety moving in his chest.

* * * * *

Some time just before 11.50am, a fire has been started by a fallen power line on the Pentadeen Spur at Kilmore East. As it races towards the Hume Highway an Incident Control Centre is established at Kilmore. The controllers are briefly hopeful that the highway, a four-lane expanse of bitumen and gravel, will act as a firebreak. But the fire barely pauses as it leap-frogs the Hume along a 5km front and hits the messmate forest on the eastern side. Somewhere in there it begins crowning, roaring through the upper canopy, leaping from tree to tree. It multiplies its intensity by a magnitude of five, then ten. The pyrocumulus cloud above swirls some 8km into the atmosphere. The fire storms through the countryside at a rate two to three times faster than predicted by the McArthur Forest Fire Danger Index.

Fire scientist Nic Gellie has commented subsequently that this astonishing speed and ferocity is changing the way some scientists think about fires, forcing them to question the orthodox concept of fire spreading in uniform ellipses. ‘Under the conditions of Black Saturday,' he says, ‘spotting, fires merging, and convection columns ruled the fire processes on the day.'

A motorist is travelling towards Whittlesea when he sees the fire coming at him. He turns around, puts the foot down. The fire begins to gain on him. He accelerates even harder; still the
fire gains. He swears later he was doing 140km/h when it overtook him.

The wind drives the flames up onto the launch-pad ridges. It shatters and snaps the tall trees, whirls the burning fragments into the valleys below or across to adjoining ridges. The experts call this spotting, but that's a feeble term to describe what it looks like to those in its path; maybe ‘saturation incendiary bombing' would be more accurate.

Massive winds whip branches and strips of bark from burning trees and whirl them so high they run into winds blowing in other directions. They are chaos in flames; they can land anywhere, and inflict incredible amounts of damage. Particularly dangerous are the long, thin strips of ribbon bark. They burn for a long time and cover enormous distances. The fires that will wipe out farms and wineries along the Yarra Valley are started by debris torn from mountain tops many kilometres away. Fire scientist Kevin Tolhurst estimates that on this day there are embers travelling a record 35km.

One CFA volunteer says later, ‘I felt like I was in the middle of a Ridley Scott movie: we were in a gully watching a shower of burning embers arc overhead, catapulting from one summit to another.'

And those ‘embers' can be huge. Later that day a policeman is driving up The Windies with no fire in sight when what he describes as ‘a firebomb the size of a caravan' comes whirling out of the sky and lands beside him. He's still blinking in shock as the missile ignites the surrounding bush, starting an instantaneous conflagration that goes racing away.

This process is repeated a thousand, a million times over as the fire careers down from Kilmore East. The front is like a spiral nebula, whirling through space and spraying great arcs of energy in every direction.

* * * * *

Bruce and Margaret Newport, in Chads Creek Road, Strathewen, feel relatively confident of their ability to defend their home. They are well equipped with pumps and tanks, and live a considerable distance from the bush on an Angus beef farm they've kept wet and green in preparation for a forthcoming field day. They are experienced country folk. When the fire approaches late that afternoon, Margaret and the children shelter inside while Bruce patrols the boundaries.

Then he watches in horror as the wind tears the roof from the building. ‘The whole thing peeled back like a tupperware lid and came off,' recalls Bruce. ‘Beams and all.'

The family survive, but only just.

When many survivors look back on Black Saturday, it is the wind that looms largest in their memory. That hot red blast was the engine that powered the juggernaut.

‘It was blowing a bloody gale up on the mountain,' says Roger Wood. ‘Never seen anything like it. I was driving a 2-tonne Pajero, and when I was out in the open it was rocking like a sailboat in a storm.'

To be in an exposed location in the bush that day was to feel that you were in the grip of a protean force: every branch, each leaf and twig was alive and writhing, straining, breaking loose, whipping away. The grasses bowed and rose as if invisible giants were running through them. One firefighter described a large limb caught up in the power lines, how it made him think of the skeleton of a galleon. As he watched it was torn apart, shattered into fragments that speared 50m through the air.

In the Kinglake Ranges it was probably worse than most places because of what fire authorities call the Ramp, where the flatlands rise into the foothills and the slope intensifies wind conditions. The result, local fire managers report, is that winds in the ranges are often twice as strong as statewide forecasts.

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A big running bushfire is an extraordinarily complex concatenation of events, a synchronicity of fuel, topography, heat, drought and human activity. But it is the wind that causes that frayed conductor on the Pentadeen Spur to snap and come crashing to the ground, sending an electrical charge arcing into the grass.

It is the wind that picks up those first thin fingers of flame and transforms them into something extraordinary, propels them in long, expanding ellipses out into the grasslands, then into the pine and bluegum plantations to the southeast.

Bureau of Meteorology data suggests that the recorded wind reached speeds of up to 120km/h. But a raging bushfire will generate its own tornadic winds, and they can be much more powerful.

Nic Gellie, who modelled the reconstruction of the Kilmore East fire for the Department of Sustainability and Environment, estimated that the wind around the fire was of cyclonic force, hitting speeds of between 150 and 200km/h. (There were no weather stations located at the fire front, so these are estimates based upon the damage done at places such as St Andrews and Strathewen, where roofs were torn from houses and massive trees corkscrewed out of the ground.)

But what is wind? And why did it go berserk on Black Saturday?

Around the world, its names are legion and rich with local memory and lore: brickdusters and mistrals, cat's paws, diabolos, doctors, the Steppenwind. There is the bitter Pittarak that whistles off Greenland's fields of ice. The suicide-inducing foehns. The firedriving Santa Anas. The Harmattan, the ‘hot breath of the desert', the name given by Tuareg nomads to the sirocco and said to derive from the Arabic for ‘an evil thing'.

Humans have struggled to make sense of wind since the dawn of consciousness. The ancient Indians saw it as the breath
of life. To the Greeks, Aeolus, the Keeper of the Winds, lived on a floating island, and is remembered for giving Odysseus the bag of winds that wreaked havoc on his journey. In Aztec theology, the god Ehecatl employed gentle zephyrs to awaken Mayahuel, the goddess of love, thereby endowing humanity with the gift of love. The Book of Genesis goes even further: when the spirit of God moves over the waters, it appears in the form of wind.

As humanity moved from myth to science, deeper thinkers sought more rational explanations. The Greek philosopher Anaximander suggested that wind was a current formed when mists were burned off by the Sun. Meteorologists would say he wasn't that far from the truth. Our contemporary understanding of wind begins with the Sun, and that instinct for balance that underlies the weather.

We think of air – well, we don't think about it at all as a rule, unless we're running out of it. But it's there all the time, it's the envelope of gases that girds our planet, and within which our respiratory systems have evolved.

You might not envisage air as having weight but it does, of course: that's what's pushing into your face when you step outside on a windy day. It is, in fact, surprisingly heavy – the air in a normal room weighs about 50kg. Each square metre of air bears down with a force equal to a 10 tonne weight, but because the pressure in liquid or gas acts uniformly in all directions and the downward force is countered by an equivalent upward force, we don't get squashed. When those particles of air develop a collective motion in a particular direction they become what we call wind.

It was the polymath Edmund Halley, he of the comet, who in 1686 first came up with a theory that approximates our contemporary understanding of how that motion works. Halley was struck by the correlation between information from two new sources: the data about air pressure provided by the recently
invented barometer and the flow of the planetary winds reported by the mariners of the expanding British Empire. He deduced that the air along the equator was heated by the Sun and lifted, to be replaced by cooler air drawn in from the temperate regions on either side of the equator – the trade winds, so crucial to the maritime industry.

Halley's observations were further refined in 1735 by amateur meteorologist George Hadley, who suggested, correctly, that the winds were affected by the Earth's rotation. The winds don't just ascend and run north or south: they tilt. Hadley also proposed that the thermal convection (warm air rising) at the equator is followed by subsidence at higher latitudes, a theory recognised today in the circulation pattern known as the Hadley Cell. Interestingly, Hadley's equatorial hot-air convection columns descend at around 30º latitude north and south, which explains the location of many of the world's deserts, from the Sahara to the Great Victorian, the Atacama to the Kalahari.

It was a cluster of those deserts, the ones that compose the vast mulga and spinifex plains of Central Australia, that would forge the terrible winds of Black Saturday.

* * * * *

In early February 2009, Australia was ringed – ringbarked, it almost seemed – by a triumvirate of high- and low-pressure systems. The procession of highs and lows that moves across our TV screens every night makes them seem like separate entities floating up there in the sky, but of course those diagrams represent patterns, not objects. Highs and lows are simply illustrations of the tendency of the molecules in the atmosphere to cluster together and move in a particular direction.

Like any other gas, air reacts when placed under pressure. Think of the air compressed inside a balloon: when given the
chance, it automatically strives to achieve equilibrium by rushing to an area of lower pressure – the space outside. The greater the difference in pressure, the greater the rush; the steeper the gradient of decline, the stronger the wind.

The atmosphere is constantly swirling around, rearranging itself in response to the shifting centres of pressure created by solar radiation. These move in great cycles, their constituent air spiralling in towards the centre of low-pressure systems and outwards from highs. One of the outcomes of the Coriolis effect – the ‘centrifugal force' generated by the Earth's rotation – is that the air cycling in and out of highs and lows flows in different directions in the different hemispheres. Here in the south, it flows clockwise into low-pressure systems and anti-clockwise around highs.

There were two significant lows affecting Australia in the days leading up to Black Saturday. The first was a monsoonal trough over northern Australia. This elongated centre of low pressure drew in vast amounts of moisture-laden air that whipped up deep convection clouds across the Gulf of Carpentaria and into Queensland (causing, ironically, widespread flooding). The ascending air associated with this cyclonic turbulence had to be compensated for by subsiding air elsewhere, and that subsidence was corralled to the southeast.

Then there was a second low over the Southern Ocean. This was drawing cold dense air northwards, pushing against the warmer subtropical air to the north like a giant bulldozer. Since the air in both these systems was flowing clockwise, the resulting airflow was being compressed, heated, driven down over the parched Central Australian deserts.

But out over the warm waters of the Tasman Sea there was a third weather system, a blocking high so powerful that it would not be budged. This had the effect of locking the lows in place. It was the reason the heatwave lasted as long as it did.

High up in the atmosphere was yet another complicating ingredient in the mix: a subtropical jet stream ripping along at speeds of up to 300km/h. The air caught in the jetstream was subsiding on one side, giving the overall flow a whirling, rotational momentum that was ultimately transferred into the surface winds tearing over and into the ground below.

These three weather systems – the monsoonal low with air flowing out from the upper reaches of its convection clouds; the southern low with its advancing wall of cold air; the blocking high – combined to squeeze the airflow of the subtropical jet stream downwards over southeastern Australia. As the dry air descended it became hotter and faster. By the time it reached the surface, it was like the blast from a furnace.

As fire scientist Liam Fogarty, Assistant Fire Chief with the Department of Sustainability and Environment, put it: