Little warning before a tsunami strikes

If you hear "unusual noises" coming from the ocean, you might only have a few minutes.

That's the stark warning from GNS Science.

Southland is to be home to a station set up at Puysegur Point while the region will be able to call on data collected from two stations in the Southern Ocean.

GNS seismologist Geoff Clitheroe said the New Zealand Tsunami Monitoring Network would give some warning of an approaching tsunami, rather than one generated nearby.

For those near the epicentre of a large earthquake in New Zealand the best warnings before any potential tsunami were natural, he said.

"If you're near water and experience strong shaking move to higher ground ... if the sea suddenly recedes or you hear unusual noises coming from the ocean. In a locally generated tsunami you may have only a few minutes."

Waves generated by seafloor movements or undersea landslides near the New Zealand coast would wash ashore before any useful warning could be issued, Mr Clitheroe said.

This was illustrated in March 1947 when two 10m waves swept ashore on the East Coast seven minutes after a heavy offshore earthquake.

The network began with a pilot site set up in Wellington in 2007 and provided information on incoming tsunami as well as detecting the first landfall of a wave on the main islands of New Zealand. It also served as a warning system for other nations around the Pacific, Mr Clitheroe said. Seven of 20 stations have been set up so far.

Of those, five are in the North Island with two on Raoul Island and on the Chatham Islands, he said.

The South Island will be home to four stations at Kaikoura, Christchurch, Dunedin and Puysegur Point in Fiordland.

In addition to the Raoul and Chatham stations, they would be sited on Norfolk, Macquarie and Antipodes islands. The stations at Norfolk Island and Macquarie Island will be installed by Australia.

GNS Science had partnered with Land Information New Zealand and the National Institute of Water and Atmospheric Research to set up the network in response to the Boxing Day tsunami in December 2004.

TSUNAMI

* Seafloor displacement from an earthquake, submarine landslip, or eruption displaces water creating waves at the ocean surface, which rush away at high speeds.

*In the open ocean, a tsunami travels fast – up to 900kmh, and is often only tens of centimetres high, but in shallow water its speed slows and its wave height grows rapidly.

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