Tsunami hazards
The entire Waitaha/Canterbury coast is exposed to tsunamis. Find out more about where tsunamis come from and the places most likely to be affected.
The biggest threats are tsunamis created by large earthquakes on the Hikurangi or Kermadec subduction zones, to the east and north of the North Island, or on the Puysegur subduction zone to the south of the South Island, 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.
Tsunami waves are not like normal waves
Normal ocean or lake waves are created by wind. They are short waves that only involve the top few metres of water and come and go off the shore quickly without flooding higher areas.
Tsunami waves are created by the displacement of water from an underwater earthquake, landslide, or volcanic eruption shifting the sea or lake floor, or a landslide into the sea or lake.
They are long waves that involve the whole depth of the ocean, not just the top few metres, so they are more powerful than normal waves created by wind.
Tsunami waves travel fast in deep, open ocean water - up to 900 kilometres per hour. When they reach shallower water near the coast, they slow down, bunch up and get higher.
Tsunamis arrive at the shore as a series of fast-moving, powerful waves or surges that continue for several hours, or even days. The first wave is often not the largest – the largest wave can arrive hours after the first wave.
Like earthquakes, tsunamis range from barely noticeable to very big. Most tsunamis that arrive on our coast are too small to flood land. However, these small tsunamis can still create strong and unpredictable currents and surges that can be dangerous for people in the water and can affect port operations.
This video of the Ihutai/Avon Heathcote Estuary after the 2010 Chile earthquake and tsunami shows how tsunami waves may not look very high, but they can pack a punch.
Occasionally, we will experience a larger tsunami that floods land. Tsunamis in 1868, 1877, 1960, 2010 and 2016 have flooded land and caused damage in Waitaha. Our geological record shows us that even larger tsunamis have happened in the past and will happen again. It is these large, rare events that we plan for.
Where tsunamis come from
The time it takes for a tsunami to reach our coastline depends on where the tsunami starts and how deep the water is on the way.
The map shows the potential tsunami sources for Waitaha and how long the first waves may take to travel to our coast. Tsunami waves travel faster in deeper water (darker blue on the map) and slower in shallower water (lighter blue).
Local-source tsunamis
Local-source tsunamis are those that can reach our coast within one hour.
Local sources for Waitaha include the Hikurangi subduction zone off the east coast of Te Ika-a-Māui/the North Island, and smaller earthquake faults and potential underwater landslides off the North Waitaha coast and in Te Moana-o-Raukawa/the Cook Strait. There are no known local tsunami sources off the South Waitaha coast.
An earthquake that may generate a local-source tsunami would be felt as a long earthquake (shaking for longer than a minute) or a strong earthquake (when it is hard to stand up). There is unlikely to be time for an official warning or for sirens (where installed) to sound for a local-source tsunami.
If you feel a long or a strong earthquake leave the red and orange tsunami evacuation zones as soon as the shaking stops. Do not wait for an official warning, siren, emergency mobile alert, or for someone to tell you to go.
Regional-source tsunamis
Regional-source tsunamis are those that could reach our coast in 1-3 hours. Sources include the Kermadec subduction zone to the northeast of the North Island and the Puysegur subduction zone south of Fiordland.
Depending on where an earthquake on one of these subduction zones occurs, we may feel it as a long (more than a minute), mildly shaking earthquake, or we may not feel the shaking at all. There may be time to issue an official warning for a regional-source tsunami, but if you feel a long earthquake (whether it is strong or not) leave the red and orange tsunami evacuation zones as soon as the shaking stops.
Map showing Waitaha's tsunami sources and how long the first waves take to reach our coast
Distant-source tsunamis
Distant-source tsunamis are those that take more than three hours to reach our coast. Sources include large earthquakes across the Pacific Ocean, particularly those off the coasts of Central and South America.
We won’t feel an earthquake that generates a distant-source tsunami, as it is too far away. There will be time to issue an official warning as most distant-source tsunamis take more than 12 hours to reach us.
Tsunami hazards
Some parts of Waitaha are more likely to experience a tsunami than others because of their proximity to tsunami sources or their particular geography.
The Kaikōura coast has a higher tsunami hazard because it is close to the Hikurangi subduction zone and other smaller offshore faults and landslides.
Pegasus Bay, Ōtautahi/Christchurch and Horomaka/Banks Peninsula also have a higher tsunami hazard because waves coming from the north or east are focussed into the area by the Chatham Rise, the shallow piece of ocean between Banks Peninsula and the Chatham Islands. Once the tsunami waves arrive, the shape of the bays and harbours tends to channel and amplify the waves.
South Waitaha has a lower tsunami hazard because there are no known local tsunami sources, and the shape of the coast tends not to amplify incoming tsunami waves.
We use tsunami hazard information to help councils plan for tsunamis, including developing tsunami evacuation zones and response plans and managing land use and infrastructure development near the coast.
Historic tsunamis
1868 Arica Tsunami
Four of the five damaging tsunamis we have experienced in Waitaha have been distant-source tsunamis from South America.
The largest of these tsunamis was the 1868 Arica Tsunami that was generated by a magnitude 8.5-9.0 offshore earthquake near the Peru/Chile border. The tsunami took 17 hours to travel across the Pacific Ocean to Waitaha. When it arrived it damaged jetties, bridges, fences, houses and boats in Horomaka/Banks Peninsula and Pegasus Bay river mouths.
You can learn more about this tsunami and its impacts on the GeoNet website..
Other distant-source tsunamis from South America in 1877, 1960 and 2010 did less damage in Waitaha but caused strong currents and inundated land in similar places to the 1868 tsunami, mainly Horomaka/Banks Peninsula and river mouths along Pegasus Bay.
2016 Kaikōura Tsunami
The tsunami generated by the magnitude 7.8 Kaikōura earthquake in November 2016 is the only damaging local-source tsunami since European settlement.
The first waves reached the Kaikōura coast within 10 minutes and deposited debris, seaweed and sea life up to 6.9 metres above sea level. The tsunami hit Horomaka/Banks Peninsula about 1.5 hours later, inundating some land in Pigeon Bay and damaging a cottage at Little Pigeon Bay.
You can learn more about this tsunami and its impacts on the GeoNet website.
2010/11 Canterbury earthquakes
The September 2010, February 2011 and June 2011 earthquakes did not cause tsunamis because they happened on land and did not disrupt the sea floor.
The December 2011 and February 2016 earthquakes were off the coast in Pegasus Bay, but the movement on the earthquake faults was not big enough to break the sea floor and create a tsunami. An earthquake under the sea floor usually needs to be greater than magnitude 7 for the movement on a fault to cut all the way up through the rocks to the sea floor to cause even a small tsunami.
You can find more information on historic tsunamis in Waitaha in the New Zealand Tsunami Database and view evidence of pre-historic tsunamis in the geological record in the New Zealand Paleotsunami Database.
Tsunami modelling reports
You can find detailed information on the areas likely to be flooded in different tsunami scenarios in the following tsunami modelling reports for Waitaha.