What size tsunami are the evacuation maps are based on?
The evacuation maps are based on a 14m tsunami. This would be a tsunami wave that rises to 14m above sea level when it reaches the coastline.
This is considered the maximum credible tsunami for our region. We refer to this sized wave in most of our information as the worst case tsunami.
What is a maximum credible event?
A maximum credible event is the tsunami generated by the largest seismic event that is expected based on our current knowledge and understanding of earthquakes and plate tectonics.
Where would a maximum credible tsunami come from?
The maximum credible tsunami would be generated by an earthquake somewhere along the Kermadec Trench. To produce a tsunami of this height, the earthquake would need to be greater than magnitude 9. This earthquake is predicted to last a long time and be felt very strongly at Tauranga.
What about tsunami from other areas?
Most tsunami have the potential to pose a marine and beach threat. Some rare tsunami could potentially overtop some of the dune systems along our coastline. Most tsunami scenarios don’t come anywhere near the worst case scenario. For instance a tsunami from White Island is unlikely to overtop the dune systems because it simply won’t be large enough to do so.
Could there be a tsunami that exceeds the maximum credible event?
Nature has a way of surprising us and our knowledge is always being added to. 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. The maps are updated whenever new information comes to hand. The most recent update is December 2016.
To be safe, the tsunami evacuation areas are larger than the area of land that may be inundated (flooded). This is to provide a buffer to ensure public safety.
Where can I view tsunami inundation maps (as opposed to the evacuation zone maps)?
Inundation maps are different to the evacuation maps. Evacuation maps show the evacuation zones and safe locations. When planning your evacuation, the evacuation maps are what you use. They are the most important.
The inundation maps are more technical. They show which areas tsunami water is estimated to flood. If you are interested in viewing these flooding areas you can view them on our mapping system, called Mapi in the Natural Hazard section.
The evacuation and inundation zones are on displayed in Mapi as separate layers. Steps to opening these layers are:
- Select I want to…
- Select Change visible map layers
- Select Natural Hazards
- Select either Max Tsunami Flood Depth at 14m or Tsunami Evacuation Zones Level2to3
Why does a 14m tsunami not reach Blake Park?
Our dune system is an excellent first line of defence against all tsunami. There is also a secondary dune system; we assume that the Mount area is flat, but 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 these dunes, even as it overtops them or travels around them. The tsunami entering from the harbour side is significantly lower than the ocean side as much of its energy and power is lost as it squeezes through the harbour entrance.
Last Reviewed: 09/12/2016