Mid Canterbury's Tsunami Hazard
All of New Zealand’s coastline is at risk of tsunami. Knowing the warning signs and then taking the right action promptly can help save lives.
A tsunami is a series of powerful waves caused by a sudden movement of the sea or lake floor, or by something falling into water. Most tsunamis are caused by underwater earthquakes, but they can also be caused by volcanic eruptions or underwater landslides. A tsunami consists of many waves or surges that arrive over several hours or even days. The first wave is often not the largest – the largest wave can arrive hours after the first wave.
When they reach shore, tsunami waves are often no higher than normal ocean waves, but they are more dangerous because they have much more water behind them so can move a long way inland very fast. Fortunately, most tsunamis we experience are not big enough to flood land, but they can cause strong and unpredictable currents and surges around the coast, which can be dangerous for people in or around the water.
Our tsunami evacuation zones are based on scientific modelling commissioned by Environment Canterbury and completed in 2022 by GNS Science.
Remember: Long or Strong, Get Gone. If you are near the coast (in a red or orange zone) and experience an earthquake that rolls for more than a minute OR makes it hard to stand up, don’t wait for an official warning. Move immediately inland until you are outside the tsunami evacuation zones. Stay there until you get the all-clear from official Civil Defence sources.
View Evacuation Zone Maps
The Ashburton District has two tsunami evacuation zones: red and orange. There is no single tsunami that would flood the entirety of both zones – rather it is an envelope around many possible 'worst-case' tsunami scenarios.
Red evacuation zone
This is an area that is most likely to be affected by a tsunami. It includes estuaries, river mouths, beaches and harbours. A tsunami of any size could cause strong currents and surges in the water. You can expect the red zone to be evacuated several times in your lifetime.
You should leave this zone immediately, if:
- You experience a long or strong earthquake
- You see sudden sea level changes or hear unusual noises coming from the sea
- You receive an official warning from Civil Defence Emergency Management
Orange evacuation zone
This area is less likely to be affected by a tsunami than the red zone. It includes areas on land that could be flooded in a large tsunami. You can expect the orange zone to be evacuated a few times in your lifetime.
You should leave this zone immediately, if:
- You experience a long or strong earthquake
- You see sudden sea level changes or hear unusual noises coming from the sea
- You receive an official warning from Civil Defence Emergency Management
No zone
Tsunami flooding is not expected in areas outside of the evacuation zones, even in a very large tsunami. You don’t have to evacuate this zone if you feel a long or strong earthquake or in an official tsunami warning. You may wish to open your home to family or friends who need to evacuate from a tsunami evacuation zone.
Yellow Zones
While not required in the Ashburton District, many places in New Zealand also use yellow tsunami evacuation zones. We encourage you to check local tsunami evacuation zones when traveling to other parts of Canterbury or New Zealand.
NATURAL WARNINGS
While the likelihood of a tsunami being created close to Ashburton’s coast is small, some tsunami sources could arrive within two hours and there may not be time to warn everyone. It is important to recognise natural warning signs and act quickly. If you are in the red or orange evacuation zones and experience any of the following warnings, don’t wait - evacuate immediately.
- Feel a long earthquake that lasts more than a minute or a strong earthquake that makes it hard to stand
- See a sudden rise or fall in sea level
- Hear loud or unusual noises from the sea (like a jet plane or train)
OFFICIAL WARNINGS
Official warnings will normally be issued by Civil Defence Emergency Management, Ashburton District Council and/or emergency services. If there is an announcement to evacuate the zone you are in, follow the instructions immediately. Stay out of the tsunami evacuation zone until you are told by an official source that it’s safe to return.
Official warnings may arrive by:
- Emergency Mobile Alert
- Radio and television
- Council website - ashburtondc.govt.nz
- Social media
- Emergency services going door-to-door when necessary
- Mid Canterbury Neighbourhood Support or community warning systems such as fire sirens
COMMUNITY WARNINGS
Many of our coastal townships have developed their own community response plans for emergencies such as a tsunami. Community warnings may include activating fire sirens or using phone trees to call affected residents. We encourage you to connect with your local community association and become familiar with the response plan for your area.
EMERGENCY MOBILE ALERTS
Emergency Mobile Alerts can only be sent by authorised emergency agencies. They are broadcast from cell phone towers to all compatible phones in a defined area when there is a serious threat to life, health or property.
Depending on how far away the tsunami is, the National Emergency Management Agency will send an Emergency Mobile Alert to phones in threatened areas telling people to EVACUATE IMMEDIATELY or to PREPARE TO EVACUATE (if the first waves are several hours away).
Regional Civil Defence groups will then send a follow-up Emergency Mobile Alert providing more detailed local evacuation information.
In the Ashburton District, many of our coastal areas do not have consistent cell phone coverage and may not receive Emergency Mobile Alerts. Learn more at getready.govt.nz
Following a long or strong earthquake or an official evacuation warning - head immediately inland until you are outside of the tsunami evacuation zones.
If possible, make a plan with family or friends who live outside the tsunami zone to stay with them if you need to evacuate. The Council will also open Civil Defence Centres if required, check the Ashburton District Council website or Facebook page for their locations.
Stay Informed – keep checking official Civil Defence channels for up-to-date information. These include:
- Council Website ashburtondc.govt.nz
- Council Facebook facebook.com/AshburtonDC
- Hokonui – 92.5 FM
- BrianFM – 99.7 FM
- RNZ – 101.3 FM
- Canterbury Civil Defence Website cdemcanterbury.govt.nz
- Canterbury Civil Defence Facebook facebook.com/CanterburyEM
- Mid Canterbury Neighbourhood Support - midcanterbury.getsready.net
Be prepared – Check out getready.govt.nz to make sure you’re prepared.
Have a plan – have an evacuation plan and escape route for your household, including pets. Think about where you would go and, if possible, plan with family or friends who live outside the tsunami zone to stay with them if you need to evacuate. Share any official warnings you hear with family and friends near the coast.
It’s impossible to predict the exact likelihood of a damaging tsunami. Large tsunamis that flood land are rare, however they can (and do) sometimes happen.
The most likely tsunamis are those that won’t flood land, but can create strong currents in the ocean, river mouths and estuaries. They are expected to occur a handful of times in someone’s lifetime.
The biggest tsunami threats for the Ashburton District are those created by large earthquakes on the Hikurangi or Kermadec subduction zones (to the east and north of the North Island), the Puysegur subduction zone (to the south of Fiordland), or by large earthquakes off the coasts of Central or South America. The place where a tsunami starts will determine how much, and what kind of warning we get.
While the likelihood of a tsunami being created close to Ashburton’s coast is small, some tsunami sources could arrive within two hours and there may not be time to warn everyone. It is important to recognise natural warning signs and act quickly.
Remember, if an earthquake is long or strong, get gone! Don’t wait for an official warning.
For more information about potential tsunami sources, please visit the ECan Website.
Why did we need to update the tsunami evacuation zones?
Scientific modelling completed in 2022 and commissioned by Environment Canterbury (ECan) showed that in rare, worst-case scenarios, flooding from a tsunami could travel further inland than previously thought.
While the overall changes for the Ashburton district are relatively minor, the updated tsunami evacuation zones will help us keep the community safe by clearly showing all areas that could be flooded and should be evacuated in the event of a large tsunami.
How accurate is the modelling?
This is the most accurate tsunami risk modelling completed for our coastline. It uses the best modelling available in the world and has been produced by GNS Science, one of New Zealand’s principal organizations for modelling tsunami risk. It has also been internationally peer reviewed.
You can find out more about the modelling on Ecan’s website.
Will this affect my properties LIM?
A Land Information Memoranda (LIM) is a document containing information that the Council holds about a property.
All known natural hazard information held by the Council is publicly accessible and included with a LIM. The revised tsunami evacuation zones will be reflected in LIMs.
Will this affect my insurance?
The Insurance Council of New Zealand advises that home and business owners should let their insurer know if their circumstances have changed with regard to tsunami hazard.
It’s also recommended that insurance details are included with your emergency grab bag.
What other work is being done?
The Ashburton District Council will mail all residents, businesses and property owners in the tsunami evacuation areas to let them know about the revised zones. Tsunami evacuation zone signs located at our coastal townships and beaches will also be updated.
Ashburton Civil Defence Emergency Management will support our coastal communities to update their individual community tsunami response plans as required and are ready to respond if required.
Other Canterbury councils have also updated their tsunami evacuation zones in response to the modelling commissioned by ECan. We recommend familiarising yourself with local tsunami evacuation zones when spending time in other coastal areas around New Zealand.
Where can I read the underlying reports?
The review of Tsunami Evacuation Zones and scientific modelling report are available on Environment Canterbury’s website.