PM - Tuesday, 14 November , 2006 18:30:00Reporter: Mark ColvinMARK COLVIN: After the devastation of the Aceh tsunami nearly two years ago, Australians have a clear idea of what a tidal wave can do. But imagine a mega tsunami, a tidal wave 10 times bigger than the Aceh event.
A group of scientists from the US, Australia, Russia, France and Ireland have been working on a theory that such mega tsunamis may happen, not every half a million years as astronomers had predicted, but every couple of millennia.
They say they're caused by meteor or asteroid impacts, which they believe have been much more frequent in earth's history than had been believed.
They call themselves Holocene Impact Research Group, and one of their members is Associate Professor Ted Bryant of Wollongong University.
He told me one factor behind the theory had been a better way of detecting where asteroids had fallen at sea.
TED BRYANT: It's a technology that's been around for about 10 years. Basically the sea surface reflects the bottom topography. So you get very small changes in the elevation of sea level across the ocean and it's a mirror image at the bottom topography. And you can pick up or measure the sea surface using altimeters on satellites.
MARK COLVIN: So the result of all this is that you think that a lot more comets and asteroids have hit Earth than had been previously thought, with devastating consequences?
TED BRYANT: Definitely and definitely. It's greater than the rate that American astronomers in Spaceguard believe is occurring.
There is a group of astronomers in Britain that don't really have objections to what we're looking at and have a higher rate of debris coming in, in the last 10,000 years.
MARK COLVIN: But what it comes down to is that instead of expecting a catastrophic impact every half a million years, you might expect one every few thousand years?
TED BRYANT: Exactly, and it might even be a shorter time frame.
MARK COLVIN: How often do you think there have been big comet impacts near Australia?
TED BRYANT: I guess now we're looking at maybe five events in the last 10,000 years.
MARK COLVIN: What kinds of effects did they have?
TED BRYANT: I mainly study tsunami and I think coming from here, we have comet impacts in the ocean, I was looking at shorelines and seeing on shorelines we have indicators of catastrophic erosion and deposition, which is beyond what storms can do and beyond what our historical record of what tsunamis can do.
Tsunamis are generated, 95 per cent of them, by earthquakes and these deposits are higher up than what an earthquake tsunami could do around the Australian coastline.
MARK COLVIN: Some people in Australia who have got 'water views' as they say, are already a bit worried about global warming. They're going to be even more worried when they hear you saying that tsunamis are much more likely, much more frequent than anyone ever expected.
TED BRYANT: Well, I have a water view and I'm not worried. There is a periodicity of about 2,500 years and there is... what the British astronomy group believe is a larger comet came into the inner solar system about 15,000 years ago and broke up and the Earth passes through the debris trail of this comet.
And it's quite common. The Earth passes through, annually, about 12 of these debris trails from different comets, broken up comets.
We tend to every 2,500 years pass through... close to the concentrated area of debris of this broken up comet and it's in a stream called the Taurids and the Taurids turn on in the end of June, you see a lot of meteorites there, small meteorites burning up in the sky.
Turns on about the third week of November, which is actually next week. The one 15,000 years ago was particularly big and its left a lot of debris and that is what we're passing through at regular periods giving rise, I think, to some of the comets... the impact craters that we're finding in the ocean.
MARK COLVIN: Your website says a tsunami will happen again sometime soon on a shoreline near you and you give people a lot of safety tips as to where to go if it happens. I mean, that sounds quite alarmist.
TED BRYANT: There I was sitting on Aceh, in Indonesia, Boxing Day at eight o'clock in the morning and if you told me a tsunami was going to come in, I would never have believed you.
And certainly if I was on Phuket in Thailand, I would have committed you to an insane asylum. If you wait long enough, a tsunami will come into any coastline of the ocean.
MARK COLVIN: Now, it's fair to say that the theories of the Holocene Impact working group are not universally accepted. How much work do you think you still have to do to get full scientific acceptance?
TED BRYANT: It'll be deadly. I'll be dead before the scientific community accepts what we believe. That's the nature of science, I mean, it's not stirring stuff out there, with people coming up with ideas and everybody gone... light bulb stuff.
I haven't been burnt at the stake, and they made Galileo recant and Copernicus, I don't know what they did to him, but no one believed him at the time and they were punished most severely.
I don't put ourselves in the same boat as Galileo or Copernicus, we're just average scientists in a range of fields who've come together and think that we're in agreement.
The scientific community, I wouldn't expect 99.9 per cent of it to agree with us.
MARK COLVIN: Associate Professor Ted Bryant of Wollongong University. 
From http://www.abc.net.au/pm/content/2006/s1788687.htm images - http://cse.ssl.berkeley.edu/SegwayEd/lessons/cometstale/images/impact4.jpg http://mapserver.mnre.go.th/tsunami/images/pic%20tsunami.jpg |
