A tsunami is a series of sea waves or surges caused by a sudden event (such as earthquakes) beneath, or near the ocean causing the water column to move and a tsunami ‘wave’ to form.
Tsunami waves travel rapidly through oceans, but as they reach shallower coastal waters the waves slow and grow in height. Onshore they may break, but more commonly cause a rapid rise in fast flowing water that can cause widespread damage, injuries and loss of life.
Tsunami form a series of waves that can be spread over a 12 hour time period, with waves arriving up to an hour apart. Tsunami travel much further inland than ordinary coastal waves and may also cause strong currents and fast rising tides.
What to do if there is a long or strong earthquake?
The only warning you will get for a tsunami caused by a local earthquake is the earthquake itself.
For more information see Tsunami - What to do
Historic tsunami in the Wellington region
The 1855 earthquake on the Wairarapa fault triggered a tsunami covering the low lying land between Miramar and Kilbirnie by approximately 1 metre. Within Wellington harbour there was flooding along Lambton Quay (which was the shoreline at the time) and the ‘tide’ was reported as rising and falling every 20 minutes for at least 8 hours. Along the Wairarapa coast, sheds 8 metres above sea level were reported as having been being destroyed by waves.
Risk of tsunami
In the Wellington region we are at risk of
- local tsunami, from earthquakes or landslides in the Cook Strait
- regional tsunami generated from the Kermedec Trench;
- distance source tsunamis from around the Pacific Ocean, but particularly those generated from South America.
In the case of a local sourced tsunami the only warning could be the earthquake itself, though unusual noises or unusual sea activity may provide possible warnings. For regional and distance source tsunami there may be time for formal warnings and evacuations.
The risk to the region depends on the source of the tsunami. A local source tsunami, while more unlikely to occur, presents a high risk because of the major consequences of such an event. A distant source tsunami (e.g. from around the Pacific) is more likely but the consequences are likely to be less, reducing the overall risk to moderate.
Tsunami zone evacuation maps
For the coastal areas of the Wellington region check out our evacuation zone map