Tsunami warning system along Christchurch's coastal area
Key things you should know if you live along the Pegasus Bay or Banks Peninsula coast:
If tsunami warning sirens sound, or you receive an official warning to evacuate, evacuate the coastal evacuation zones for your district. You will have several hours to evacuate.
If you feel a moderate long (more than one minute) earthquake, evacuate the coastal evacuation zones for your district. Do not wait for the sirens, or for an official warning - the earthquake is your tsunami warning. You will have at least one hour, possibly two or three, to evacuate.
If you feel very strong ground shaking, in which it is hard to stand up (at least a magnitude 6 earthquake), there is a very small chance that a small tsunami has been generated. Move immediately away from the coast, estuaries or river mouths at least two blocks inland. If you cannot quickly move at least two blocks inland (e.g. if you live in Southshore) consider going to the upper storey of a two storey building, or up onto a high sand dune - the highest sand dunes along the Pegasus Bay coast are higher than the expected worst case local source tsunami. DO NOT WAIT FOR SIRENS, or for an official warning - the earthquake is your tsunami warning. You may only have 5-30 minutes to evacuate.
If you are at all able, evacuate on foot or by bicycle to avoid traffic jams. You are much more likely to get out if you are on foot or on a bicycle and you will leave more room on the road for those people who must use a car.
What is a tsunami?
Pacific Ocean tsunami travel time map
A tsunami is a series of waves which occur when a large volume of water is rapidly displaced. Tsunamis are categorised into three groups – local, regional and distant source.
Local source tsunami are generated less than one hour’s travel time from the coast.
Regional source tsunami are generated one to three hours travel time from the coast.
Distant source tsunami are generated more than three hours travel time from the coast.
A tsunami may occur when a large volume of water is rapidly displaced. This may occur due to:
- A large underwater or coastal earthquake;
Underwater volcanic eruptions;
Underwater landslides (which may be triggered by an earthquake or volcanic activity);
Large coastal cliff or lakeside landslides.
Local Source Tsunami – Information for coastal Christchurch and Banks Peninsula
The chances of a local source tsunami being generated by an earthquake in Pegasus Bay are low. This risk has not changed as a result of the recent earthquakes.
However, it is still important to know what to do if one does happen as there will be no time to issue an official warning for a local source tsunami.
Warning signs
Natural signs may be your only warning. Be ready to act if you are at the coast or within two blocks of the coast and experience any of the following:
Feel strong ground shaking that makes it hard to stand up;
See a sudden rise or fall in sea level;
Hear loud and unusual noises from the sea.
What to do
If you are on the beach or within two blocks of the coast, estuary or a river mouth and feel strong ground shaking that makes it hard to stand up:
Move quickly inland or at least two blocks away from the coast, estuary or river mouth or to higher ground (at least four metres high). Use the safest route that you can. Within those first two blocks every step that you move inland or up hill, the safer you will be.
If you can't quickly and safely get away from the coast, estuary or river mouth within five minutes (e.g. if you are in Southshore) then consider moving to the upper storey of a multi-storey building, or to the nearest high dune. You should aim to be at least four metres above sea level if you are still within two blocks of the coast. It is unlikely the water from a tsunami in Pegasus Bay would go higher than this.
Only use your car if you have to.
You will need to use commonsense to work out the best route to use from where you are located.
Be aware that if the ground shaking is strong, there may be unstable cliffs and rockfall in hillside suburbs. Think about weather conditions.
It is YOUR responsibility to determine the best place for you and those with you to move to.
Regional Source Tsunami – Information for coastal Christchurch and Banks Peninsula
A regional source tsunami may come from the east and north of the North Island or from off the Fiordland coast.
The most likely regional tsunami source is the Hikurangi subduction zone off the Wairarapa/Hawke’s Bay coastline. Earthquakes are thought to occur here every few thousand years but the timing of the last earthquake in this area is not known. A tsunami from this fault would take between one to two hours to reach the Christchurch and Banks Peninsula coast. It is unlikely to be large, but it may flood low-lying areas.
Sea heights above normal tide height at the coast would probably be between one to two metres, but could be higher than this in some localised areas because of the way tsunamis slosh around in Pegasus Bay.
Warnings
It is likely that there will be time to sound the tsunami warning sirens (when installed) for a tsunami generated in the Hikurangi subduction zone. However, the most important warning will be the natural warning signs.
Be ready to act if you are at the coast or within two blocks of the coast and experience any of the following:
Feel a moderate, rolling earthquake that lasts for a minute or more;
See a sudden rise or fall in sea level;
Hear loud and unusual noises from the sea.
If you have concerns, do not wait for an official warning or for the sirens to sound. Evacuate if you feel it is the safest thing to do.
What to do
If you are on the beach or within two blocks of the coast, estuary or a river mouth and feel a moderate rolling earthquake that lasts a minute or more:
Move quickly inland or at least two blocks away from the coast, estuary or river mouth or to higher ground (at least four metres high). Use the safest route that you can. Within those first two blocks every step that you move inland or up hill, the safer you will be.
You should aim to be at least four metres above sea level if you are still within two blocks of the coast. It is unlikely the water from a tsunami in Pegasus Bay would go higher than this.
Only use your car if you have to.
You will need to use commonsense to work out the best route to use from where you are located.
Be aware that if the ground shaking is strong, there may be unstable cliffs and rockfall in hillside suburbs. Think about weather conditions.
It is YOUR responsibility to determine the best place for you and those with you to move to.
Distant Source Tsunami – Information for coastal Christchurch and Banks Peninsula
Christchurch Coastal Evacuation Zones: Cordons and traffic flow Evacuation procedures (based on info available at April 2010)
[ larger view ]
The most likely tsunami to impact on coastal Christchurch and Banks Peninsula is one generated off the coast of South America or Alaska. Historically, all damaging tsunamis to affect coastal Christchurch and Banks Peninsula have been generated by earthquakes off the coast of South America – in 1868, 1877, 1960, and most recently in February 2010.
A tsunami generated off the coast of South America will take between 12 to 15 hours to reach the Christchurch and Banks Peninsula coastline.
The areas most at risk from distant source tsunamis are coastal areas from Brooklands/Kainga to Sumner, and low-lying areas of Banks Peninsula. Tsunami wave heights are likely to be higher in the bays and harbours of Banks Peninsula than on the Pegasus Bay coastline due to the funnelling affect of the narrow inlets. Distant source tsunamis are unlikely to be greater than five metres above normal sea level on arrival at the coast.
In the event of a distant source tsunami being generated, there will be time to issue an official warning, and when installed, the tsunami warning sirens will be activated.
Warnings
Official warnings will be issued on radio and television. It is important you listen for local information in these messages, as the forecast tsunami effects will vary along different parts of the New Zealand coastline.
The NZ Police and Christchurch City Council have identified 19 “at-risk” sectors within the Christchurch coastal zone which will be the focus of any evacuation activity (see map right). About 23,000 people in 8570 households will be involved in a total evacuation of the zone.
Arrangements are in place that all available NZ Police, Fire Service (NZFS), Christchurch City Council Park Rangers and Response Team personnel, and Canterbury Civil Defence Emergency Management Group Response Team personnel would start to evacuate residents from identified risk sectors.
A standard message will be delivered to residents at each property within the sector by members of the evacuation team. Evacuation personnel will take the details of special needs required by evacuees or those refusing to evacuate.
When installed, the tsunami warning sirens will be sounded if scientific and technical experts, emergency services and Christchurch City Council officials are of the opinion that public safety is threatened.
You may also receive a tsunami warning through an unofficial source, such as from friends, family, social media sites or international media reports.
What to do
If you receive an unofficial warning - verify this information if possible.
Listen to the radio for official warning information. Local radio stations to listen to are:
Confirmation of official warnings will also be available from a range of websites including:
If you are requested to evacuate, follow the instructions of emergency services and/or civil defence personnel. Leave the area and do not return until you are told it is safe to do so.
- Move to a safe area outside the Coastal Evacuation area – to friends or family or to the alternative location identified in your own emergency plan.
- You can evacuate to higher ground (e.g. Mt. Pleasant Road, Evans Pass Road, Summit Road) – at least 15m above sea level is recommended.
Evacuation routes
The coastal evacuation map (see map above) identifies preferred routes leading out of evacuation sectors. If you are required to evacuate, take the route closest to your home or workplace (follow the direction of emergency services personnel).
Harbour Road -> Kainga Road -> Marshlands Road (Kainga)
Spencerville Road -> Marshlands Road (Spencerville)
Lower Styx Road -> Marshlands Road (Styx)
Beach Road -> Mairehau Road (Northshore)
Bowhill Road -> Travis Road (North New Brighton)
Lonsdale -> Keyes -> Rookwood -> Travis (North New Brighton)
Seaview Terrace -> Pages Road (New Brighton)
Bridge Street -> Breezes Road (South New Brighton)
Bridge Street -> Dyers Pass Road -> Linwood Avenue (Southshore)
Rocking Horse Road -> Estuary Road -> Bridge St (Southshore)
Main Road -> Ferry Road (Redcliffs, Sumner)
Wakefield Avenue -> Evans Pass Road -> Summit Road (Sumner)
Ferry Road or Hargreaves Road (Ferrymead)
Bridle Path Road -> Tunnel Road (Heathcote Valley)
Cordons will be set-up by the Police and the Council’s roading contractors at key points to:
Cordons will be maintained until it is safe for people to re-enter the evacuation area.
Preparedness
Arrangements for schools
Schools and Early Childcare Centres are required to have plans detailing their response to emergency events. Ask at your School or Early Childcare Centre what arrangements they have in place and the steps you are expected to make to collect your child(ren) following an evacuation.
Arrangements for rest homes and retirement villages
Rest Homes will be evacuated by their staff to pre-arranged safe assembly areas outside the evacuation zone or transported to an evacuation centre. The ‘pre-arranged’ self assembly areas will be identified in the Rest Homes Emergency Plan – it is likely to be a Rest Home outside the evacuation zone with the capability to temporarily provide evacuated residents with a similar level of care.
Find out about the arrangements you are expected to make to contact with your family members following an evacuation at a Rest Home/Retirement Village.
Self evacuation
Residents in the Coastal Evacuation Zone may evacuate the area before an official evacuation order. If you feel it is unsafe for you and/or your family to remain in the area – leave.
Readynet alerting system
The Christchurch City Council encourages education centres, residential care centres, medical facilities, businesses, community groups, and residents associations to register their emergency planning arrangements on the Readynet© web-based emergency planning system. The Council and Emergency Services are able to issue alerts to those registered on Readynet© via txt message or email. These alerts will be forwarded to nominated contacts with information regarding a current or predicted emergency event. More information on this system can be found here.
Other useful links
Further information on local source tsunami risk and other tsunami information for Christchurch following recent earthquake events can be found on the Environment Canterbury site.
For more details about the risk to Canterbury you can view the Q-files. These are available from: www.ecan.govt.nz/hazards
GNS Science also provides links to frequently asked questions about tsunami.
