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Ten years ago, our nation's capital was ravaged by one of the country's worst fires. Four lives were lost, and over 500 homes. But the extent of the devastation caused by the Canberra fires baffled scientists and emergency services.

Dr Jason Sharples

It was a pretty big shock, 'cause I mean, there's nothing really in the literature which suggests the fire should spread that fast, or could spread that fast.

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In the aftermath, it was clear that the worst damage was due to something much more savage than an ordinary firestorm.

Rick McRae

There was a police car that was picked off the ground and dumped into a stormwater drain. There was a series of streets on the southern edge of Chapman, which had suffered severe wind damage as well as fire damage, and that was difficult to explain.

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What hit Canberra had never before been documented in science.

Cameraman

Holy shit!

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A fire tornado. On January the 8th, 2003, a huge, dry lightning storm struck in multiple places across the ACT, sparking a large number of fires. One of the biggest began here in the Brindabella Ranges. But for days, fire conditions weren't particularly alarming.

Stephen Wilkes

Very orderly fire behaviour. Very orderly progression across the landscape.

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Then, on the 18th of January, the situation turned catastrophic. Dry westerly winds came into play. Temperatures reached 37 degrees, causing surface air to mix with the upper atmosphere, creating strong gusts.

Anja Taylor

It's an incredible view.

Stephen Wilkes

So the fire started over there in the valley. It steadily moved along that ridge until it got to a point into fresh fuel, and this whole area was ignited within about 20 minutes.

Anja Taylor

This whole area?

Stephen Wilkes

This whole area was alight.

Rick McRae

At that stage, it was perhaps the biggest fire event that this area had seen for quite a long time.

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Stephen Wilkes was in a chopper at 2pm that day mapping the fire.

Stephen Wilkes

I was trying very hard to find out where the front of the fire was to give us an idea of how fast it was coming into town, and there was no front. The fire had broken up into thousands of smaller fires. We were seeing things that none of us had ever seen, knowing things were wrong, but not being able to make any sense of it. Suddenly it all went quiet, and the chopper pilot turned to me and said, 'Steve, I don't think we're gonna get out of here,' and I looked around and I realised that if I panicked at all, I was probably dead. As we left, I took a photograph of what I saw was a slight rotation, and some light coming through the plume, and we believe that was pretty close prior to the tornado forming. To be honest with you, I've only recently realised how lucky I was.

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The next day, Stephen returned to document the damage.

Stephen Wilkes

We were speechless, we were devastated. The houses that were alight and wind damage that was done. There were massive trees - fully mature yellow box trees - just torn up out of the ground, moved a few metres, and dumped. What kept coming to my mind was a tornado.

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In the science literature, fire tornados didn't exist but as researchers slowly pieced together information from aerial and ground surveys, no other explanation fit.

Rick McRae

This is the damage path that was mapped from the air soon after the event, and it shows it extending from around Mr Coree through to the suburb of Kambah.

Anja Taylor

That looks quite a long path.

Rick McRae

It extends a total of 25 kilometres. It was just under half a kilometre in width before it hit the city.

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Whatever ripped through the suburb of Chapman hit the Pierce Pine Plantation first. Amidst the blackened trunks, it left a distinctive trail of destruction.

Rick McRae

The trees had all been snapped off at about 3 metres above the ground. The alignment of the trees left lying on the ground was indicative of a vortex.

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Softwood trees, like pines, can only snap off when wind speeds reach a level equivalent to 2 on the Fujita Scale of tornado intensity, the highest being 5. At this strength, trees can be uprooted, cars lifted off the ground, and roofs torn off.

Rick McRae

All of this supported our claim that the wind speeds were around 250 kilometres per hour.

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But ironically, the real clincher was areas where there was no damage at all.

Rick McRae

The key part of it is the fact that these gaps are in here. A tornado is able to lift off from the ground and reattach later, and these gaps support the notion that it is a tornado. The alternate hypothesis, a fire whirl, isn't able to lift off from the ground. It's attached to the hot fire ground.

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As the evidence came together, extraordinary images emerged of the tornado itself, helping to define the characteristics of the vortex.

Dr Jason Sharples

The tornado in the photo corresponds to about 2cm, so that means that the base of the tornado must have been about half a kilometre wide there.

Rick McRae

Half a kilometre. That's amazing.

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It's 4pm in Kambah District playing fields, a very different-looking afternoon to when Tom Bates stood here watching the fire roar over the hill.

Anja Taylor

So where did you first see the tornado coming?

Tom Bates

Oh, on Mount Arawang here. It arced across the top of the hill. Spot fires along the bottom.

Anja Taylor

Yeah?

Tom Bates

Stood up on this side. It was just like a great big wave ready to burst.

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Incredibly, Tom caught the moment on film.

Tom Bates

I've never in my life seen anything like it. Holy mackerel!

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At the far right, the funnel of the tornado comes into view.

Tom Bates

This is rather frightening. Oh, I'm getting pelted with stuff. Stinging the daylights out of me. Sheets of tin floating. You can hear it in the camera. Power lines going down.

Rick McRae

No-one has captured a tornado like that as clearly in a fire situation before. One of the interesting things about the video was a pair of football goalposts in the foreground - that gave us a measurement stick in the vertical direction, so we could go out to where the video was taken and we could measure the speed of movement over the ground, and also the wind speeds within the vortex. We were able to estimate the vertical wind speed of over 150 kilometres per hour.

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Scientifically documenting a fire tornado was a world first, but that left a vital and more important research question. How could a series of relatively contained fires develop so quickly into such a violent, pyro-convective event?

Dr Jason Sharples

I guess I was really interested in trying to understand what caused the thunderstorm, which spawned the tornado.

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In the multispectral line scans taken on the day, Dr Jason Sharples was struck with the same puzzling images again and again - sections of the fire spreading sideways.

Dr Jason Sharples

These are instances where the fire, where it would normally be spreading downwind, have started actually spreading across wind, and what we found were these instances, without exception, were connected with lee-facing slopes.

Anja Taylor

I'm on a lee-facing slope, facing away from hot westerly winds. Normally these are considered the sheltered sides - the safest areas to take cover from a fire - but in the case of the Canberra fires, it was these slopes that burnt the fastest and the most intensely.

Dr Jason Sharples

Framed a hypothesis that this phenomenon was being caused by the interaction between the fire, the wind, and the terrain, so what we did in Portugal was to try and emulate these conditions in a combustion tunnel.

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In the experiments, the fire behaved exactly as it did in Canberra, racing up the lee slope and channelling sideways as it hit the headwind. Multiple spot fires were created, igniting large tracts of the slope. Before these experiments confirmed it, no-one knew a fire could behave in this way. Here's what's going on. The wind travels up slope, but as it hits the crest, it's moving too fast to follow the terrain, and lifts off, swirling back on itself in an eddy. The fire moves with it, and the disastrous result is that two sides of the hill light up at the same time with extraordinary speed.

Dr Jason Sharples

It turns a small fire into a very big fire very quickly. Rather than spreading as a fire front, as it normally would, it causes what we call deep flaming. So that's where you get large tracts of the landscape all igniting in a relatively short amount of time.

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The intense and deep flaming caused by the fire-channelling events happened immediately before the thunderstorm formed.

Anja Taylor

With such a huge area alight, a massive amount of energy was released into the atmosphere. In fact, in the peak ten minutes of flaming, more energy was released than the Hiroshima atomic bomb.

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The massive smoke plume of heat and moisture formed a gigantic pyro cumulonimbus cloud - a huge supercell thunderstorm. Stephen took these incredible photographs as it formed. As the moist, hot fire plume is lifted into the upper atmosphere, it's hit by upper level winds of a different speed and direction, setting up a vortex, and a tornado is born. As for fire tornados, the team hopes never to see another one, but they're even more hopeful that their discoveries on fire behaviour may one day save lives.

Rick McRae

When it comes to an extreme fire, we have learned an awful lot about how to stay safe, and how to protect the community. The real challenge now is getting those learnings out, right across the bushfire industry.