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Common questions on tsunami maps

The evacuation maps are based on a maximum credible tsunami wave that rises to 14m above sea level when it reaches the coastline. To provide an extra buffer, the tsunami evacuation areas on the maps extend beyond the area of land that is predicted to be flooded by a maximum credible tsunami.

Where would a maximum credible tsunami come from?

The maximum credible tsunami could be generated by an earthquake along the Kermadec Trench, north-east of New Zealand. To produce a tsunami of this height, the earthquake would need to be greater than magnitude 9.

What about tsunami from other areas?

Most other tsunami scenarios modelled are not as damaging as the Kermadec scenario. While most tsunami have potential to affect our marine and beach areas, only a rare tsunami could potentially overtop some of the dunes along our coastline. A tsunami from White Island is unlikely to overtop the dunes.

Could a tsunami exceed the maximum credible event?

The evacuation maps are based on our current best knowledge. The knowledge includes in-depth studies undertaken in 2012, 2013, 2014 and 2015 by GNS Science and Tonkin and Taylor. These studies are peer reviewed by technical experts to ensure they are accurate and utilise the most up to date information and methods of research available. Nature has a way of surprising us and our knowledge is always being added to. The maps are updated whenever new information comes to hand. The most recent update was in February 2017.

How can Blake Park be safe?

Our dune system is an excellent first line of defence against all tsunami. The tsunami water will lose a lot of power as it encounters the dunes, even as it overtops them or travels around them. There is also a secondary dune system at Mount Maunganui. Some of the roads sit quite a bit higher than the streets either side. The tsunami water will lose a lot of power as it encounters the dunes, overtops them or travels around them. Meanwhile, the tsunami entering from the harbour side will be significantly lower than the ocean side because much of its energy and power is lost as it squeezes through the harbour entrance.

How can the high ground at Gordon Spratt Reserve be safe?

The dune system along Papamoa has an average height above mean sea level of about 8m, so when a 14m wave hits the dunes, only the top 6m of the wave flows onto the land. Once a tsunami hits land it loses about 1m of height for every 300m it travels inland. Tsunami water will also lose a lot of energy when it crosses the Wairakei Stream. The top of the high ground sits at least 3m above the highest predicted water level. It is designed to survive an earthquake, liquefaction, and scouring from tsunami water.

Why walk?

It’s natural to think you’ll be able to leap into the car and get away before everyone else. But what if everyone else is thinking the same thing? Consider this: if everyone tries to drive out of Papamoa at the same time, traffic modelling undertaken by NZTA shows that it will take at least 6 hours to get everyone clear. That’s on a good day with no emergency or damage to roads from the earthquake. The best plan is to go by foot. The evacuation maps we have provided show safe locations and zones that can be reached by foot from most parts of the coast within 40 minutes. The distances are modelled on a very conservative walking pace.

What if I need assistance?

With less than an hour after a major earthquake before a tsunami arrives, emergency services will not be able to get you out in time. The reality is that you’re on your own. The community’s best chance to survive a tsunami is to work together as a community. Make an evacuation plan with your neighbours, especially if you know they will need help getting to a safe area. If you live in a retirement village or gated community, make sure you know what the emergency plan is.

Why do I need an emergency pack?

Tsunami can arrive in several waves over a long period of time. The first wave is not always the biggest. That is why you need your emergency pack. Pack anything you think you will need, like medicine and a water bottle. You should be prepared to wait for many hours before the water subsides.

Where can I view tsunami inundation maps?

Inundation maps are different to the evacuation maps. Inundation maps show with more precision areas where tsunami water is predicted to flood. If you are interested in viewing these you can view them on our mapping system, called Mapi in the Natural Hazard section. You will need to select the Natural Hazards layer, then select either Max Tsunami Flood Depth at 14m or Tsunami Evacuation Zones Level2to3. 


Last Reviewed: 03/02/2020

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