A tsunami is a series of powerful ocean surges that is caused by a large volume of the ocean being displaced – often by an undersea earthquake.
Most tsunamis resemble very strong, fast tides, rather than waves. These can penetrate a long way inland. Much of the damage from tsunamis is caused by the strong currents and floating debris.
All of New Zealand's coastline is at risk from tsunamis.
- If a tsunami is triggered by a distant earthquake, New Zealanders may get several hours warning before it arrives here.
- However, if it is triggered by an earthquake close to our shores, there may be no time for official warnings – or only minutes.
Be prepared for a tsunami
If you live near the coast:
1. Know the risks to your property: contact your local council and ask to see their tsunami evacuation zone maps. Also ask what official warning methods will be used in your area if a tsunami is imminent.
2. Know where the nearest high ground is (at least 35 metres above sea level) and have a plan for how to get there quickly.
3. Prepare an emergency plan and survival kit.
What to do when a tsunami is imminent
- You've felt a large earthquake.
- The sea draws back – like an unusually low tide – or you hear a strange noise from it.
Warnings may come in the form of:
- Official warnings from Civil Defence. These may be via the emergency services, TV or radio, loudhailer, or a siren.
- Word of mouth. If friends or neighbours tell you they've heard a tsunami warning, don't wait around to confirm this – get to higher ground first.
What to do:
1. If you're near the coast, leave for higher ground immediately.
2. If you can't get higher, go at least 1.5 kilometres inland.
Walk or bike if possible. If you travel by car, you may get caught in a traffic jam. If you do need to drive, keep going until you're well out of the evacuation zone, to make room for others behind you. If you decide to leave your car and walk, park it off the road.
As you run out the door, grab your getaway kit.
3. If you can't get to higher ground, go to an upper storey or climb onto a roof or tree.
During a tsunami
1. Most tsunamis have a number of surges ('waves') – not just one – and the first is often not the largest. Therefore, you must stay in your safe place for many hours after the first wave.
Wait until you get an official 'all clear' before returning to lower ground or the coast.
2. If you get caught in the tsunami, try to get out of the water and onto a floating object.
After a tsunami
1. Keep informed by listening to the radio.
2. When re-entering your home, check for damage and if you can, take photos for insurance purposes.
- Get Thru tells you more about how to prepare for and respond to a tsunami.
- GeoNet uses seismic sensors to identify potential tsunami-generating earthquakes occurring off the New Zealand coast. It also operates tsunami gauges across the greater New Zealand region.
- The US Geological Survey website has scientific simulations and animations of recent tsunamis.
- The Pacific Tsunami Warning Center issues tsunami warnings and advisories for the region.
- Within New Zealand, the Ministry of Civil Defence and Emergency Management is responsible for tsunami warnings.
EQC sponsors Te Papa's Awesome Forces exhibition, which shows how plate tectonics, earthquakes, volcanic eruptions and erosion have shaped our landscape – and the lives of the people who live here.
Te Ara tells the story of tsunamis in New Zealand’s history – from archaeological findings and Māori oral tradition, to those produced by the Wairarapa earthquake of 1855 and the large waves that hit the east coast of New Zealand following the Chilean earthquake of 1960.