New Zealand has a tsunami gauge network that consists of water level recorders on open coasts, as well as at Raoul and Chatham Island. They transmit data continuously to GeoNet, and unusual changes in water level may indicate that a tsunami has arrived at the gauge location.
Warnings of distant tsunamis
For warnings of tsunamis from distant sources, New Zealand relies on the Pacific Tsunami Warning Center, based in Hawaii. If a large submarine or coastal earthquake greater than magnitude 6.5 occurs, they issue a tsunami information bulletin. They then monitor data from a network of coastal tide stations and deep ocean sensors, and if a tsunami is detected, they issue tsunami watches and warnings for areas that may be affected.
Tsunami Watch bulletins from the Pacific Tsunami Warning Center are received by New Zealand’s Ministry of Civil Defence and Emergency Management, which convenes a panel of tsunami experts to determine the hazard. They then 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, internet apps, social media or websites, phone text alerts and electronic highway notice boards. Some areas also use sirens.
Tsunamis from major earthquakes off South America may take 12 hours or more to reach the New Zealand mainland, giving authorities time to prepare and if necessary evacuate coastal settlements.
If an earthquake is LONG or STRONG, GET GONE!
If you are on the coast during an earthquake that is strong or lasts longer than a minute, hear unusual noises from the sea or see water rising or receding from the shore, move immediately to the nearest high ground or as far inland as possible. If you do not have time to move to higher ground or inland, go to an upper storey of a sturdy building. Stay away from coastal rivers and streams, and never go to the coast to look for a tsunami.
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 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. It is important for the public to be aware of natural warning signs, and act quickly.
Following major tsunamis in the Indian Ocean and Japan, New Zealand regional councils [and local authorities] developed tsunami zone maps and evacuation plans for population centres. Some areas have introduced signs showing evacuation routes, and safety zones marked by blue painted lines on streets and footpaths.
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, Chile tsunami 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 a major tsunami evacuation. Warned by nationwide radio broadcasts (‘A wave is reported approaching at 400 miles an hour’) 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. 1
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 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.
Other tsunami warnings
Between 2005 and 2016, Civil Defence warnings were issued for a number of tsunamis – from earthquakes in southern Fiordland and the Pacific Ocean near Samoa in 2009, from Chile in 2010, from the Japanese Tohoku tsunami in 2011 and more Chile earthquakes in 2014 and 2015. None caused any substantial damage in New Zealand.
The Magnitude 7.8 Kaikōura earthquake sequence on 14 November 2016 triggered tsunami along the east coast of New Zealand. Hundreds of people were evacuated from their homes to higher ground in Kaikoura and from low-lying suburbs of cities such as Wellington and Christchurch. However, conflicting reports meant that warning sirens in some areas, such as Wellington, did not sound until after the waves had arrived. There was also confusion among the public over how to respond to the sirens.