Tsunami

A  tsunami is a series of water waves (called a tsunami wave train ) that is caused when a large volume of a body of water, such as an ocean, is rapidly displaced. The Japanese term is literally translated into "harbor wave."

Earthquakes, volcanic eruptions and other underwater explosions (detonations of nuclear devices at sea), landslides and other mass movements, bolide impacts, and other disturbances above or below water all have the potential to generate a tsunami. Due to the immense volumes of water and energy involved, the effects of tsunamis can be devastating.

Know your tsunami evacaution zone.

Tsunami hazards

Tsunami result from the displacement of water caused by earthquakes, underwater landslides, volcanic eruptions or even meteorites.

A series of waves spreads out across the ocean like ripples when a stone is thrown into a pond.

The waves can be tens of metres high when they break onshore. However, smaller tsunami (less than one metre in height) are more common. These come onshore as non-breaking waves, rather like a rapidly rising tide.

In the Wellington region, tsunami may be caused by distant earthquakes near South or North America. Local tsunami can be caused by undersea landslides in the Hikurangi Trough or Cook Strait or by earthquakes on an offshore fault.

A local tsunami, caused by the 1855 Wairarapa earthquake, washed over Lyall and Evans Bays and flooded shops along Lambton Quay.

Do we get any warning?

A tsunami that starts overseas can take hours to reach New Zealand. Emergency management agencies will make sure that local communities are warned. Warnings will be broadcast over the radio and television.

If a nearby earthquake or landslide causes a tsunami, there may only be a few minutes warning - or no warning at all!

If you feel a strong earthquake or hear a tsunami warning, move inland or to higher ground. Listen to a radio for further advice. Never go down to the beach to see a tsunami arrive.

More information:

Tonkin & Taylor Consultants 2002. Options for Managing Risks from Tsunami in the Wellington Region, Wellington, Tonkin & Taylor

GeoEnvironmental Consultants, 2002. Wellington Regional Tsunami Hazard Scoping Project. Lyttelton: GeoEnvironmental Consultants

Gilmour, A. and Stanton, B. 1990. Regional Natural Disaster Reduction Plan - Seismic Hazard: Tsunami Hazards in the Wellington Region. Lower Hutt: Department of Scientific and Industrial Research

Saunders, W. 2000. Tsunami hazard in the Wairarapa. Masterton: Greater Wellington Regional Council