Hawke's Bay's position on the Pacific Ocean means that the area occasionally experiences tsunami from both local, regional and distance sources. Tsunami (pronounced tsu - nam - ee) is a Japanese word meaning 'harbour wave'. It describes a series of fast travelling waves caused by large disturbances on the ocean floor, such as earthquakes, landslides or volcanic eruptions. In the deep ocean tsunami pass almost unnoticed, but as they approach land and therefore shallower coastal waters, they change dramatically - a 1-2 metres at sea grows into waves that can be over 30 metres in height.
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Tsunami Display at National Aquarium of NZ
The tsunami display is located at the National Aquarium, Marine Parade, Napier. This interactive learning centre highlights the risks of tsunami, particularly on the east coast. Animations show how tsunami are caused, the history of New Zealand tsunami events (with some real life experiences) and safety information on what to do when a tsunami warning is issued. It was developed by NIWA (National Institute of Water and Atmospheric Research), GNS (Institute of Geological and Nuclear Science) and Hawke's Bay Regional Council. There is a large display screen which makes viewing easier for large groups of people, especially for school groups. The National Aquarium is open 7 days 9am - 5pm (7pm in summer holidays). For school visit bookings phone 834 1404 or email info@nationalaquarium.co.nz.
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| Turihara - Debris left by local tsunami north of Gisborne 26 March 1947 |
Previous impacts on Hawke's Bay
Although there are few historical records of tsunami striking the Hawke's Bay coastline, the records show that the area could be impacted by tsunami generated by both local and distant sources. Damage has been fairly minimal in the past, partially because large parts of the coastal region remained sparsely settled until recent times. However, with the development of housing areas to take coastal residential areas, tsunami from local sources are a greater threat.
Localised Tsunami
Details of past tsunami in Hawke's Bay are scarce and based solely upon written European records of the events. Although most historical events have not posed major hazards, localised damage has occurred. These result from earthquakes or undersea landslides. The subduction zone between the Pacific and Australian plates lies off the coast of Hawke's Bay and at least one huge, ancient landslide underwater has been mapped that lies near the fault.
In early February 1931, there were a number of reports of events related to the Hawke's Bay Earthquake:
- A large wave was reported in Waikare Estuary, which appeared to have been caused by an earthquake-generated landslip on the other side of the estuary. The wave destroyed a wool shed and strew fish on grass about 15 m above high tide level.
- In Waikokopu Beach, at the base of Mahia Peninsula, three 'tidal waves' were reported, bringing fish and shellfish on the beach. A large rock was also thrown on a train, but the driver miraculously escaped without injury.
- A 3 m surge or wave was also reported racing up the Wairoa River shortly following the earthquake.
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| Miss Higgins of Napier stands on the front foundation of her parents boat shed which was moved back and wedged between other buildings in 1960 |
Distant tsunami
Distantly-generated tsunami have also been reported in Hawke's Bay and three which had a great impact in Hawke's Bay were generated by large earthquakes off the coast of Chile in 1868, 1877 and 1960. Records of the 1868 and 1877 tsunami are not extensive as many of the reports were destroyed by fire during the 1931 earthquake.
In 1868, there was a variation of 1.8 m in tide level in Napier and the water receded far enough to expose the wreck of the Montmorency. In 1877, the tide was ebbing and flowing every alternate hour, and Watt's Wharf was completely flooded due to the high water level.
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In May 1960, more serious damage was reported in Napier. The gas main was broken and 40 m of a footbridge in Ahuriri Estuary was destroyed. A number of pleasure boats were damaged or swept out to sea. Buildings were flooded and moved, endangering the lives of the Napier Sailing Club's caretaker and his family, and 1700 m3 of sand was scoured from the boat harbour.
The exact heights of the waves were not recorded, because the mechanical gauge malfunctioned, but they are thought to have reached up to 3 m.
More recently, oscillations of less than 0.10 m were recorded as a result of an earthquake in the Kuril Islands in October 1994.
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What to do?
Natural warnings
If you are at the coast and you experience any of the following:
- you feel a strong earthquake (it's hard to stand up or walk steadily, there is significant household contents damage and building damage [classified as Modified Mercalli MM6-MM7]),
- you feel a weak earthquake that lasts for a minute or more
- you see strange sea behaviour, such as the sea level suddenly rising or falling
- you hear the sea making loud and unusual noises or roaring like a jet engine
Then get to high ground or go inland.
Do not wait for an official warning. Instead, let the natural signs be your warning. First protect yourself from falling objects then immediately get to high ground or go inland. Wait for official all clear. The first wave may arrive within minutes, or take more than an hour to arrive.
Official warnings
Official warnings are expected to come for sources that are more than three hours of tsunami travel time away from Hawke's Bay.
- An official warning from Civil Defence Emergency Management may be issued through radio or television broadcasts.
- Warnings may also be through siren, telephone, loud hailer or other local arrangements.
- You may receive warnings from one, or several sources. Respond to the first warning, do not wait for more messages before you act.
- Listen to your radio and follow any official instructions.
- Evacuate from the areas or zone(s) stated in the warning.
- Take your `Getaway Kit' with you.
- Stay out until the official 'all-clear' is given.
Informal warnings
- Warnings from friends, other members of the public, international media, internet, etc. may be correct. Informal communication may be your only warning especially for tsunami from less than three hours tsunami travel time away from you.
- If you feel the threat is imminent, quickly get to high ground or, if the surrounding area is flat, go as far inland as possible.
- Verify the warning only if you can do so quickly (via NZ TV/Radio broadcasts, internet, Civil Defence Emergency Management, Police, Fire).
- The first or largest wave may not arrive for 6 hours after the forecast arrival time.
If New Zealand Civil Defence Emergency Management warnings are available, trust their message over informal warnings.
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