Page 4 – Living with tsunami hazards
Warnings of distant tsunamis
For warnings of tsunamis from distant sources, New Zealand relies on the Pacific Tsunami Warning Center, based in Hawaii and established in 1949. The Centre receives seismic data from over 150 stations around the Pacific basin. If a large submarine or coastal earthquake greater than magnitude 7.5 occurs, they issue a regional tsunami warning to areas where a tsunami could arrive within three hours, and a tsunami watch for areas where it could arrive within six hours. They then monitor data from a network of tide stations and sea-floor pressure gauges, and if a tsunami is detected, they issue a tsunami warning for the entire Pacific basin.
Warnings from the Pacific Tsunami Warning Center are received by New Zealand’s Ministry of Civil Defence and Emergency Management, who in turn notify regional authorities, the police and New Zealand Defence Force, and local emergency organisations. The public can be alerted via nationwide radio and television broadcasts.
Tsunamis from major earthquakes off South America may take 12 hours or more to reach the New Zealand mainland, giving authorities a number of hours to prepare and if necessary evacuate coastal settlements.
Warnings of local tsunamis
Tsunamis produced by local sources such as offshore earthquakes may arrive at the coast in just a few minutes. This is not enough time for New Zealand’s national earthquake monitoring system, GeoNet, to locate the earthquake, determine if it could produce a tsunami, and notify the Ministry of Civil Defence and Emergency Management, who would then issue a warning. It is important for the public to be aware of natural warning signs, and take basic safety precautions.
If you are at the coast and feel an earthquake or see water receding from the shore, as soon as possible move at least 35 metres uphill or more than a kilometre inland. Stay away from coastal rivers and streams.
Museum of New Zealand Te Papa Tongarewa is on Wellington Harbour, which has been hit by tsunamis in the past and is at risk from major earthquakes and tsunamis. The building was designed so that no art or artefacts are displayed or stored on the ground floor. In an earthquake that might result in a local tsunami, museum staff will move visitors to the upper floors.
Evacuating the coast, 1960
On 23 May 1960, a tsunami from a magnitude 9.5 earthquake in Chile caused damage in New Zealand coastal areas. Two days later, just before noon on 25 May, a radio message from Hawaii said that a tsunami from a major aftershock of the Chile earthquake might hit New Zealand within about an hour and a half. It sparked the only major tsunami evacuation ever to be carried out in New Zealand. Warned by nationwide radio broadcasts (‘A wave is reported approaching at 400 miles an hour’) 1 and telephone messages, port facilities along the east coast were cleared, schools in low-lying coastal areas were closed and the children taken to safe areas.
Almost the entire populations of Whitianga, Mercury Bay, Waihī Beach, Whakatāne, Ōhope, Ōpōtiki and Kaikōura headed for high ground. It was the largest evacuation in New Zealand’s history. The warnings, however, had an unintended side-effect – many people went to the coast to watch the tsunami arrive. It proved to be very minor, and hard to separate from the fluctuations still continuing from the main tsunami. Had it been larger, however, many onlookers could have drowned, as tsunami waves travel much faster than people can run.