A tsunami is a series of sea waves generated by an earthquake, a large underwater landslide or volcanic activity.

All of New Zealand is at risk of earthquakes and all of our coastline is at risk of tsunami. We can't predict when one will happen, but we can protect ourselves and our families.

The most tsunami-prone areas in New Zealand are between the East Cape and Napier, the Cook Strait area, the area around Banks Peninsula and the East Coast of the South Island.

An international warning system, based in Hawaii, attempts to predict any activity that could lead to a tsunami in the Pacific Ocean by combining information from earthquake sensors with ocean buoys. The buoys used to identify and track tsunami are positioned hundreds of kilometres offshore. Tsunami can be generated from inshore of these buoys and this is a particular risk along the Hikurangi Trench subduction zone off the lower East Coast of the North Island.

Know the signs

Official warnings

If there is time, you will receive official warnings from Whanganui District Civil Defence and Emergency, Horizons Regional Council or through the Ministry of Civil Defence and Emergency Management. These warnings may come to you via social media, radio broadcasts or the emergency services (such as Police, Fire, or Ambulance).

You may receive warnings from one or several sources. In an official warning there will be instructions to evacuate from the zone(s) stated in the warning message. You may also receive a warning through the Emergency Mobile Alert.

Unofficial warnings

Warnings from friends, the public, or international media, may be correct. Evacuate from all zones if you are concerned. Verify the warning once you are in the safe zone.

Remember: Long or Strong, Get Gone.

Tsunami – natural signs

In the case of:

  • a large earthquake (one that is hard to stand up in)
  • a weak rolling earthquake shaking of unusually long duration (a minute or more)
  • out of the ordinary sea behaviour, such as sudden sea level rise or fall and/or unusual noise...

You should evacuate all zones – a wave may arrive within minutes, wait in the safe zone for the official all clear. For a local source tsunami which could arrive in minutes, there won't be time for an official warning.

Find out where the tsunami evacuation areas are in Whanganui and check your address to see whether your home is within the zone.

Tsunami sirens

Civil Defence sirens have been installed at Balgownie Avenue, Castlecliff and Mowhanau to help warn people of tsunamis. These are briefly tested at around 0830 on the first Wednesday morning of each month excluding January.

Sirens will only be activated continuously if Civil Defence is aware of an earthquake from a local or distant source and there is likely to be some time for people to evacuate to higher ground. Distant source tsunamis may take up to 14 hours to impact on our coastal areas.

The continuous sounding of sirens sited along the coast and the lower Whanganui River estuary up to Pūtiki will give warning that an emergency is taking place.

The tsunami warning sound at Mowhanau comes from a large, mechanical siren, which has an air raid-like sound.

If you hear a tsunami siren, please listen to your radio and visit the Whanganui District Council Facebook page to find out what to do next.

What to do before, during or after a tsunami

Tsunami information boards

Tsunami information boards are situated around Whanganui's coastal areas. The boards include information on natural tsunami signs and what to do if a tsunami is generated near our coastline.

Signs indicating the evacuation routes and safe location zones are also displayed along coastal areas.