Tsunami in Hawke's Bay

A tsunami is a series of fast traveling waves caused by large disturbances on the ocean floor, such as earthquakes, landslides or volcanic eruptions. In the deep ocean, tsunami pass almost unnoticed, but as they reach shallow coastal waters nearer to land, they change dramatically - a wave of one-to-two metres at sea can grow into waves measuring more than 30 metres in height. A tsunami is made up of very turbulent water – even a small tsunami wave can knock you off your feet.

Hawke's Bay's is at risk from:

Near-source tsunami: Our biggest is risk is from the Hikurangi subduction zone (sometimes called the Hikurangi Trench), just off our coast – this is New Zealand’s largest active fault. If the subduction zone ruptures in a large earthquake, it may  rapidly send a tsunami towards our coast. If you feel a Long OR Strong earthquake, it may mean the subduction zone has ruptured and a tsunami is on the way. If you live in a tsunami evacuation zone (red, orange or yellow): Get Gone.  There will be no other warning so evacuate immediately and use every minute wisely. Do not waste the time trying to find information online.

Regional and far-source tsunami: Because of New Zealand’s position in the Pacific Ocean, the east coast is also at risk from tsunami travelling from much further away. In this case, you will not feel an earthquake and there will be enough time to get expert advice, issue warnings and organise an orderly evacuation.

For a near-source event natural warnings, like any of those below, will be the only warning of a tsunami, so don’t wait for official warnings, go immediately to high ground or, if the surrounding area is flat, go as far inland as possible. Evacuate all tsunami evacuation zones (red, orange and yellow), if any of the following occur:

• A STRONG earthquake which is hard to stand up in
• A weak, rolling earthquake which is unusually Long; a minute or more
• You see unusual sea behaviour, such a sudden sea level fall or rise, or the sea is making loud and unusual noises, especially roaring like a jet engine.

First, check if your home, school or workplace is in a tsunami evacuation zone here.

Understand what that zone means

All zones (red, orange and yellow) must evacuate if there is a Long or Strong earthquake.

In the case of tsunami coming from far away, providing lots of warning time, specific zones may be asked to evacuate by Civil Defence Emergency Management.

Plan your evacuation route

Walking, running or biking are better than driving, because roads may be damaged in the earthquake or there may be too many cars on the road, causing traffic jams. The aim is for you and your family to be safe.  There is a route guide for those who live or work along the Napier and Hastings coastline: Plan your route - it can be difficult to know in which direction it is best to head in some of these areas.

Remember you may have to take this route at night. Know the route, practice it with your family, and have a torch. Aim to have more than one route too, in case you need to change route on the day.

If you are in a coastal tsunami evacuation zone and there is a Long OR Strong earthquake don’t wait for an official warning. There will not be time. Go immediately to high ground or, if the surrounding area is flat, go as far inland as possible. 

If you are in the water, get out immediately and move to higher ground or inland – staying in the water is very dangerous.

We get a lot of queries about vertical evacuations during a tsunami. ‘Vertical evacuation’ means evacuating to a high floor of a building, instead of leaving the tsunami evacuation zone.

Japan has structures specifically designed for vertical evacuations, and the US has building standards for them. Those include foundations that are very deep and reinforced to a higher standard than most buildings, and an open ground-floor level to allow water to flow through.

While New Zealand adopted building standards for vertical tsunami evacuation structures in December 2020, this is for new especially-designed buildings and so we can’t say that any existing buildings in an evacuation zone are a safe place in a tsunami.

We advise you to leave evacuation zones, making sure you carefully exit any building, while being aware that there may be failing debris, and follow your route to a safe location.

But we understand that there may be some rare situations that require different decisions. They may include that:

• You are not sure you will be able to get out of the tsunami evacuation zone to a safe location in time. If there is a multi-level, sturdy building on your evacuation route that you can access, you could choose to go up – look for reinforced concrete or structural steel buildings.
• Those who are in a high-rise building may decide to stay there. They may feel uncomfortable leaving their building and making their way through streets – possibly in the dark, and with damage from the earthquake. This is something you and your household or workplace will need to discuss and decide.

While vertical evacuation could be an option in some circumstances, you need to be aware the building might not withstand the impact of a tsunami. You could also be isolated in a building for days before help can get to you, and there is the risk of fire. If you choose to evacuate vertically, you should go to at least the third floor. If your building doesn’t have a third floor, staying is not a good option.

Each option has risks and we cannot advise one over the other. You need to be comfortable with your own choice.

Whatever you decide works for you, we strongly recommend you spend some time putting together an Emergency Grab  Bag (one at home and one at work if both are in evacuation zones), and practice the route you would take if you have to leave your building. Knowledge is power: the more you prepare for this now, the better.

Our message for tsunami remains: If you are in any of the evacuation zones and feel an earthquake that is either longer than a minute OR strong enough that it’s hard to stand up, then get to high ground as soon as the shaking stops. If it’s Long OR Strong - Get Gone.

Once you are in a safe place, search on radio or online for information on the situation. Remember, the first tsunami wave may not be the biggest and there are likely to be many waves. Wait for an official 'all clear' before returning to a tsunami evacuation zone. 

Check the Boat tsunami advice for the appropriate safe distance for boats to evacuate during a near-source tsunami, remembering that if you are out on the water in a local tsunami you only have 10 minutes to make a decision and take action.

Why are we at risk?

New Zealand’s entire coast is at risk of tsunami but the East Coast of New Zealand has been identified as having the highest tsunami risk because of the subduction zone marked by the Hikurangi Trough.

Scientists have confirmed the subduction zone could generate severe tsunami from earthquake sizes of Magnitude 8-9.  This means in the future we could see tsunami like those in the Indian Ocean in 2004 and in Japan in 2011.

Everyone should be familiar with the Hawke’s Bay tsunami hazard maps which can help residents and councils prepare for the impact of a large tsunami. These maps show the worst case scenarios – a tsunami from a very large 2,500 year return period local earthquake or one coming across the Pacific Ocean.   Our risks include destruction of homes, businesses, productive land and infrastructure in inundation zones, along with injuries and loss of life, environmental devastation and the slow process of recovery.

In Hawke’s Bay we have been assessing our coastal hazards from Clifton to Tangoio. Find out more on this website. 

In 2015 a project also began studying the Hikurangi plate boundary as the source of earthquakes and tsunami. Find out more on this website.

Local-source tsunami

Several moderate-size tsunami have been observed along the Hawke’s Bay coast in the 160 years or so of written historical record. On several occasions, the lives of Hawke’s Bay people have been threatened.

3 February 1931: the largest earthquake in the Hawke’s Bay’s history, the magnitude 7.8 Hawke's Bay earthquake, initiated a moderate tsunami:

• At Waikokopu Beach, near Mahia Peninsula, three waves deposited fish and shellfish on the beach.
• A three-metre surge was reported racing up the Wairoa River shortly after the earthquake.
• A large wave was reported in Waikari River. This appears to have been caused by an earthquake-triggered landslide on the other side of the estuary. The wave destroyed a wool shed and deposited fish on grass about 15 metre above high tide level.

26 March 1947: the worst effects of a tsunami were experienced on the coast north of Gisborne, where the waves were 10 metres high. In Hawke’s Bay, Mahia Peninsula was affected.

Distant-source tsunami

Tsunami from far-off locations have caused damaging tsunami surges in Hawke's Bay. The 1868, 1877 and 1960 tsunami generated by large earthquakes in South America have had the greatest impact. The surges lasted several days in each case, the largest of the surges generally occurring within the first 24 hours.