Waves of fear

by Ruth Laugesen / 26 March, 2011
Our world has been knocked sideways. We're already scared of earthquakes - how worried should we be about tsunami?
There's beached - and then there's beached-as. Like the whales that were stranded high on the Miramar Peninsula hills that look south over Cook Strait, near Wellington Airport.

One whale skeleton was found 800m inland, and 45m above sea level. It was 18m long, according to a scientist who examined the skeletons in 1912. The bones were "crumbing to powder, yet preserved in a form of dry sand".

So how did the whales get there? Was the cause:

a) Giant birds of prey, now extinct, that plucked the whales from the sea and carried them to ridge-top eyries to feed their young?

b) An unconventional Maori hapu that preferred sweeping skyline views to the more usual seaside barbecue and dragged the whales there?

c) A massive earthquake that lifted the Miramar Peninsula out of the sea, and the surprised whales to high ground?

d) Whales were members of a lesser known cetacean cult in which those nearing the end of their life shimmy uphill in a bizarre suicide pact?

In the absence of any better explanations, says Professor James Goff, co-director of the Australian Tsunami Research Centre at the University of New South Wales, the answer is probably e), a very large tsunami stranded the whales. There appears to have been uplift of about 10m in the area, which meant the sea level would have had to rise a scary 35m to leave the whales there.

Not that anyone seems particularly fussed. The whale skeletons are gone because houses have since been built on the site.

New Zealanders are relatively sanguine about tsunami risk, perhaps unaware that the country has the fourth highest risk of tsunami in the world, after Japan, Hawaii and Indonesia. Or perhaps we haven't got around to obsessing about tsunami because we are already worrying about earthquakes, volcanoes and our towering foreign debt.

Goff, an Englishman who lived here for 15 years, sounds mildly relieved to be living in Australia now, despite the poisonous snakes and forest fires. He is in Christchurch when we talk to him, looking at earthquake damage, but is now heading for Japan.

"I used to say somewhat flippantly to people, you don't live in New Zealand if you're scared of hazards. This is a happening place. Anything nasty goes in New Zealand, and bang, we've gone and been caught out with Christchurch.

"We didn't even know about the bloody fault that caused it, and yet we've been studying faults in New Zealand for 100 years. It does need a kick in the teeth like this to make us realise there's an awful lot out there we still don't know."

Goff rates New Zealand science as "bloody good", with plenty of cutting-edge research. But he says a country of this size, with limited scientific resources and many hazards, is bound to have more Christchurch-like blind spots.

With tsunami, too, the picture is incomplete. The high-risk zone is thought to stretch along the east coasts of both North and South Islands, and includes Wellington, the whole of Northland, and the Coromandel. Tsunami can be triggered by quakes in South America, faraway Japan, or the Pacific, or locally in the Hikurangi subduction zone to the east of the country, or on localised faults.

In the wake of the 2004 Asian tsunami, tsunami planning suddenly stepped up, led by Civil Defence. Local authorities in higher-risk areas are preparing hazard maps, evacuation zones and tsunami warning signs and increasingly putting up sirens.

The trouble is, whereas the warnings for tsunami generated in Japan and Chile come with hours of notice, the warning time for potentially lethal localised tsunami is perilously short. A big quake on a fault near New Zealand could unleash a wall of water moving at great speed, reaching land in 30 to 45 minutes. There would be no sirens.

"There's no way a warning system can respond that fast," says Rob Bell, principal coastal hazards scientist at the National Institute of Water and Atmospheric Research. Japan has the most sophisticated tsunami warning system in the world, but with a tsunami generated so close to shore, that clearly wasn't enough.

Instead, the standard Civil Defence advice is if the ground shakes severely and you are near the sea, head for high ground, and fast. "You can't get a better warning than the ground shaking underneath your feet," says Ron White, Civil Defence manager for the Thames Valley. He says in many cases cars will probably not be a safe way to get out quickly, because of the likelihood of bottlenecks and traffic jams.

In the Tauranga area, the release of tsunami hazard maps last year brought alarm in the community. According to the Bay of Plenty Times, the map showed an extreme tsunami - a surge of 6.75m - would inundate about 19,000 homes and 2000 commercial premises, and smash through Tauranga's entire low-lying coastal strip. Some 35,000 would be forced to flee. Mt Maunganui and Papamoa would be devastated. A more refined map is due to be published in July.

Tsunami hazard maps that are gradually being produced for the entire coastline repeat the picture of large areas of vulnerability.

In Wellington, markings have been put on selected roads in at-risk suburbs like Island Bay, reading "Tsunami Safe Zone". The intention is to show people how far they have to move inland to avoid a big wave.

But Goff says this is another example of the experts pretending to know more than they do.

"People think they stand on one side of that sign and they're safe. I find that extraordinarily dangerous. That line is based upon modelling. Mathematical modelling only ever approximates, it estimates, it doesn't get it right."

Unfortunately, says Goff, many sites not seen as high tsunami risks could turn out to be dangerous.

When he was working as a scientist in New Zealand, Goff looked for tsunami signs all around the country, not just in known tsunami sites. "I've found tsunami deposits around almost all of New Zealand."

He found evidence of tsunami deposits in Taranaki, but was told it wasn't worth studying because "we haven't got any big faults there". "And I said, how do you know, you haven't looked? And that's the problem. I don't think there's any particular piece of the coastline where you can sit there and say, bah, you won't get tsunamis here. Even the west coast of the South Island has had tsunami."

With the rash of tsunami since the shocking Asian event of 2004, is there something going on? Tsunami experts disagree.

Waikato University senior lecturer in earth and ocean sciences Dr Willem de Lange thinks there is some sort of a pattern. Since 2004, major tsunami have hit south of Java Island in 2006, the Solomon Islands in 2007, Samoa in 2009, and Sumatra in 2010. The previous significant grouping was in the 1960s. "The work we've done suggests tsunami occur in clusters. The last cluster was from about 1952-1964, about a dozen years, then there's this one that started in 2004. If that holds then we could expect a few more of these in the next six years."

But Goff disagrees, saying so little is known about the long historical record of tsunami that it is hard to tell from this close up what is a cluster and what is a blip. But he thinks we shouldn't get the recent extreme events in Christchurch and Japan out of proportion.

"This is not unusual. This is normal Mother Nature activity. Sometimes you get a few big ones fairly close together, and then sometimes there's a long gap before anything happens. There is no Armageddon building up here.

"You've got all these plates floating around on top of the Earth and they have arguments with each other from time to time. The problem is we've had a reasonably quiet period, and people have got used to living their nice cosseted lives without being affected by the environment they live in, and now the environment is biting back. It's not pleasant."

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