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Published: 2011-03-14 00:00:00

The Mercury Bay Community Board will next Tuesday 22 March receive a briefing on plans for a new Eastern Coromandel Tsunami Strategy, which will initially focus on responding to the risks posed to Whitianga.

The development of the strategy - a joint initiative from Thames-Coromandel District Council and Environment Waikato – follows new data indicating the risk of tsunami hitting the east coast of the Coromandel Peninsula is higher than previously understood.

While the new data does not provide cause for immediate alarm, it has led to the two councils starting to discuss the future management of tsunami risks with eastern Coromandel communities. The Japanese tsunami has highlighted graphically the threats posed by big tsunamis.

Whitianga, which lies at the head of Mercury Bay, has been chosen as the first community to consult with as its unique geography means it is considered the centre most at risk from the impacts of tsunamis.

The factors that make Mercury Bay and Whitianga particularly vulnerable to tsunamis include:

  • The bay faces east towards the sources of tsunamis which means they can sweep straight into the bay.
  • Mercury Bay acts like a funnel which can concentrate the impacts of tsunamis on Whitianga.
  • The natural characteristics of the bay mean that tsunami waves can be amplified and they can also tend to bounce off the shoreline back into the bay many times – in 1960 this led to tsunami affects sloshing around in the bay for four days.
  • These natural characteristics are why Whitianga – along with the Otama-Whangapoua coast – have previously been judged at highest risk from the impacts of tsunamis.  The 1960 tsunami – caused by an earthquake in Chile - was larger at Whitianga than at any other place on the mainland.

“We will be giving the Mercury Bay Community Board a detailed briefing on the issues and inviting their participation in the development of a community consultation strategy aimed at finding out how local people think the risk should be managed,” said TCDC’s strategic relationships manager Peter Wishart.

 “Given the potential for significant loss of life and property damage in a big tsunami, we are very keen to hear the community’s views.”

EW emergency management officer Adam Munro said Whitianga has been hit by many tsunamis over the centuries.

“The 1960 Chilean earthquake produced waves that inundated significant areas of the town. In 1868 and 1877, large earthquakes in southern Peru and northern Chile affected many parts of New Zealand’s east coast, including Whitianga. These were ‘distant source’ tsunami,” Mr Munro said.

“Recent studies indicate that distant source tsunamis from South America may be more frequent than previously understood – about once every 50 to 100 years. The good news is they take 12-15 hours to reach New Zealand, hopefully providing people with time to evacuate.

“However, new scientific work indicates large tsunami waves can also be produced by earthquakes along the Tonga-Kermadec Trench to the north-east of Whitianga. These ‘local source’ tsunami would take about one hour to reach Mercury Bay, meaning much less time to evacuate. Their likely frequency is also higher than previously understood.”

Mr Wishart said a number of local arrangements were already in place to warn of tsunamis that were generated from distant sources such as South America. But people would have far less warning of any tsunami generated by a big earthquake closer to home – the first sign they might get of a threat was actually feeling the shake themselves.

“So, given the new insights we’ve received into the potential frequency of tsunamis affecting Whitianga and the Coromandel’s other coastal communities, we now want to start looking at what more the Whitianga community wants us to do to manage the long-term risks tsunamis pose in our area.

“Questions we’re asking include whether we should refine our emergency management procedures or change our planning and development rules to prevent, for example, a kindergarten or resthome being built in the likely path of a tsunami.”

Besides causing deaths and injury, it is estimated a large tsunami hitting Whitianga could cause up to $174 million worth of damage.

“So another question we’re asking is how can we manage this risk to property better to protect the community’s material prosperity,” said Mr Wishart.