A tsunami with the same devastating force as the Indian Ocean tsunami could affect coastal areas of New Zealand, local scientist says.
“The size of the tsunami surge that came ashore in Thailand was no more or no less than we could expect along a limited section of our coast for a smaller earthquake or landslide or whatever,” says Dr Hugh Cowan from the public research Institute of Geological and Nuclear Sciences, who lead a team of New Zealand scientists in Thailand in the aftermath of the Boxing Day tsunami.
That would be a tsunami triggered by an earthquake, or a volcanic eruption, or a submarine landslide within 30 or 60 minutes travel time of the New Zealand coast.”
In Thailand the waves were a torrent of water 10 to 12 metres high, a height, Dr Cowan says, that has already been seen in New Zealand in the past.
“We know from the historical record that such surges and waves have come ashore in some parts of New Zealand. They would only need to come ashore along a populated section of our coast to have almost identical consequences,” he said.
However, a tsunami along the length of the coast of New Zealand is unlikely. “We are not necessarily anticipating or modelling the impact of such an event along the entire New Zealand coast line but into Gisborne, or into Napier, or into eastern Christchurch or into Whakatane or into Whitianga. These are communities that are potentially at risk.” For instance, in 1947 a 10-metres tsunami wave came ashore north of Gisborne.
For New Zealand the lesson from the devastation in Thailand, Dr Cowan says, is that no single measure can provide complete protection. “It’s protection, warning, response, long-term planning for critical facilities.”
He says that in such an emergency saving lives is the key objective “That’s about evacuation or refuge and that’s about getting people above the wave height or beyond the threat. That’s all about either providing warnings or self-evacuation. It’s really based on public knowledge, people knowing what to do when they think the game’s up and trying to support that public knowledge with effective warning and effective means timely.
The tsunami hazard for the Pacific is higher for other oceans because of the “Ring of Fire” — the zone of earthquakes associated with the tectonic plate boundary that bounds the Pacific.
In New Zealand, scientists consider there are two main tsunami hazards — pan-Pacific events for which there will be some warning (in 1960, an earthquake in southern Chile sent a tsunami sweeping across the Pacific) and “near source” tsunami generated by large offshore New Zealand earthquakes, landslides, and volcanic eruptions.
For tsunami in the Pacific, the Ministry of Civil Defence and Emergency Management would receive warnings in most cases many hours in advance from the Pacific Tsunami Warning Center in Hawaii.
However, these warnings only give arrival times, and have no way of estimating the size of the wave. In 1960, when an advance warning was given, many people went down to the sea to get a better view of the approaching wave.