Tai āniwhaniwha Tsunami

A tsunami is a series of waves generated when a large volume of water in the sea or a lake is rapidly displaced by an earthquake, landslide, meteorite, or volcanic activity.

Tsunami are described by how long it may take to reach the nearest coastline.

Local-source tsunami can arrive at our coast within minutes. They are generated close to Aotearoa New Zealand and are very dangerous because of their short arrival times. This means that they have no or very little warning time.

Regional-source tsunami are generated between one and three hours from Aotearoa New Zealand. A large earthquake in the Southwest Pacific, or an eruption from an underwater volcano in the Kermadec Trench to the north of our country, are two possible triggers for regional-source tsunami.

Distant-source tsunami take at least three hours, and in some cases 14 hours or more, to arrive. A distant-source tsunami that reaches our shores is most likely to be generated by a very large earthquake in the Pacific Ocean, particularly off the South American coast.

New Zealand is at risk from local, regional and distant source tsunami. A very large tsunami has the potential to inundate multiple coastal areas at once, causing widespread loss of life, and damage and disruption to the built and natural environments. This can occur across multiple regions. resulting in significant economic and social impacts. We have a long history of living on the coast, and some of our largest cities are in coastal areas, therefore our exposure to tsunami hazard is high. 

Tsunami risk and history in New Zealand

Tsunami are often thought of as an unlikely hazard in New Zealand as not many have caused damage in recent times. However, our historical tsunami record suggests New Zealand has experienced multiple, very large tsunami in the past. Since 1840 there have been as many as ten recorded tsunami with wave heights greater than four metres at the coastline.

Even small tsunami reaching New Zealand can result in damaging currents, as seen in Whitianga due to the Tōhoku, Japan Earthquake and Tsunami of 2011.

More than 80% of the world's tsunami are generated in the Pacific Ocean and, like Japan, some of New Zealand’s biggest tsunami are generated by earthquakes close to our shores.

Warnings and what to do

In most cases there is often not enough time to provide an official warning for tsunami. This is because a wave can arrive in minutes, which is much quicker than scientific analysis allows us to assess if a wave has been generated and where and when the wave may reach the nearest coastline. This is why it is important to act on natural warning signs.

This means, move as far inland as possible, or to your nearest high ground if you experience a long or strong earthquake. Some councils in New Zealand show where tsunami safe zones are located. Make sure to familiarise yourself with your local and regional tsunami hazard risk management practices and evacuation zones.

Each tsunami will impact our coastlines differently. Tsunami can travel a long way inland - especially up rivers - causing extensive damage in their travel path.

The impact of a tsunami can range from unnoticeable to devastating and it depends on the characteristics of each event: the distance from its point of origin, its size (based on the source) and the configuration of the bathymetry (the depth of water in oceans) along the coast that the tsunami is approaching.

The volume of water displaced, and velocity of tsunami waves can result in total destruction at the coast.

The waves that initially hit the coast, followed by inundation inland, can cause serious damage to property, infrastructure and land.

Tsunami waves may smash into the shore like a wall of water or move in as a fast-moving flood or tide.

Small tsunami will approach land as a strong, fast-moving tide and can result in damaging currents.

You can find out more information about tsunami and their impacts on the Earth Sciences New Zealand website.open_in_new

Tsunami can be fatal and cause severe property damage. The depth and speed of a tsunami will influence how a tsunami could damage your property. Common property damage can include:

• Undercutting of foundations
• Scour and erosion of land
• In some cases, tsunami can result in structural damage to homes and buildings

We are always working to better understand how we can support our communities to better understand tsunami impacts. Current work includes knowing what the likely impact a tsunami could have on people and property, so we can more adequately strengthen buildings and critical infrastructure, to ensure we’re even more prepared.

• Learn how to make your home saferopen_in_new
• Search your address in the Natural Hazards Portal to find out which hazards may affect your property.
• Read more about tsunamiopen_in_new and how they can affect people and places.
• Check that you have the right insurance in placeopen_in_new, including home insurance that may qualify you for natural hazards cover.
• Check your local council website for information about local hazards and emergency planning in your area.