What is a tsunami?
A tsunami is a series of powerful waves with strong currents. They are mostly caused by underwater or coastal earthquakes and sometimes by underwater landslides or volcanic eruptions.
Where do tsunami come from?
Tsunami can come from different sources.
A distant source tsunami, like one generated from Chile, could take 14 hours or more to arrive. A regional source tsunami, like one generated from the Southwest Pacific, could take between one and three hours to arrive. In these cases we will have time to issue official warning messages.
A local source tsunami generated from an earthquake close to New Zealand, can arrive at New Zealand coastal areas within minutes.
In this case, official warnings are unlikely to be issued before damaging waves arrive, so people in coastal areas need to take immediate action – if you feel an earthquake that makes it hard to stand, or lasts more than a minute – move immediately to higher ground or as far inland as possible.
The three types of tsunami
There are three distinct types of tsunami. The type you encounter depends on the distance you are from the place where it is generated.
- Distant tsunami: Are generated from a long way away, such as from across the Pacific in Chile. In this case, we will have more than three hours warning time for New Zealand.
- Regional tsunami: Are generated between one and three hours travel time away from their destination. An eruption from an underwater volcano in the Kermadec Trench to the north of New Zealand, could generate a regional tsunami.
- Local tsunami: Are generated very close to New Zealand. This type of tsunami is very dangerous because we may only have a few minutes warning.
Warning messages and signals about a possible tsunami can come from several sources – natural, official or unofficial.
- Natural warnings: For a local source tsunami which could arrive in minutes, there won’t be time for an official warning. It is important to recognise the natural warning signs and act quickly.
- Official warnings: Official warnings are only possible for distant and regional source tsunami. Official warnings are disseminated by the Ministry of Civil Defence & Emergency Management to the national media, local authorities and other key response agencies. Your local council may also issue warnings through local media, siren and other local arrangements.
- Unofficial or informal warnings: You may receive warnings from friends, other members of the public, international media and from the internet. Verify the warning only if you can do so quickly. If official warnings are available, trust their message over informal warnings.