First tsunami warning sirens for Hurunui

The first tsunami warning sirens for the Hurunui district have now been installed.

The sirens have been erected on poles outside the community centres at both Amberley Beach and Leithfield Beach.

These sirens will be triggered manually, though technology is available to allow them to be remotely triggered via radio or phone in the future.

Emergency Management Officer, Allan Grigg says while, as the recent Christchurch earthquake showed,  people are likely to head away from coastal areas on their own account, the sirens are designed to provide extra ‘peace of mind’ for residents that they will have as much warning as possible to evacuate if necessary.

The sirens don’t sound like the traditional “air raid” sound, relying instead on Morse code, to distribute audible warnings.

Dash – dash – dot – dot - tells people to leave beaches, tune into the radio for information, and be prepared to evacuate. This is the ‘alert’ signal.

Dot – dot – dot – requires people to evacuate immediately to nearest safe high ground. This is the ‘warning’ signal. 

A continuous uninterrupted tone signals the all clear. People can then return to their homes.

These are the first tsunami warning sirens for Hurunui, and Allan Grigg says the installation is certainly timely given the recent 7.1 shake that rocked Christchurch and Kaiapoi and rattled many in our district.

“They should provide a degree of reassurance to the residents of these two coastal areas a solid warning system is in place should a large wave head our way in the future.”

The Hurunui coastline is open to two potential tsunami threats: an underwater landslide into the Kaikoura Canyon, or a large scale earthquake in South America, either of which could send a wave of up to four metres in height towards our shoreline.

“While a tsunami causing earthquake off the coast of South America is our most likely tsunami threat, at the same time it also provides us with the most amount of time to react – anywhere up to 14 hours – compared to 30 minutes or less if a tsunami was generated from a shift in the continental shelf.”

In February 2010 a series of tsunami surges generated by a large earthquake in Chile did strike the Canterbury coast, the first raising the sea level in Lyttelton Harbour by 2.2 metres in less than an hour.

The surges breached the shores of the harbour and bays on Banks Peninsula, flooding paddocks, submerging jetties, washing across roads and damaging boats. Fortunately the largest surges arrived around low tide, which saved coastal Christchurch from damage.

Amberley and Leithfield Beaches were chosen as the initial siren locations because they are the most densely populated coastal settlements. If the system proves successful the Council will consider them for the other beach townships and settlements in the district.

The sirens will have their first real test in the early evening of Wednesday October 20th.

All three signals – alert, warning, and all clear – will be sounded.

The test will confirm the true range of the sirens in the two beach settlements.

Allan Grigg says it is likely not all parts of the settlements will hear the sirens and residents will need to ensure their neighbours are aware of their sounding.

The sirens will in future be tested twice yearly, at daylight savings time

 For further information contact:                

Allan Grigg

Emergency Management Officer

Hurunui District Council

03 314 8816

www.hurunui.govt.nz

 

Background information:

A tsunami is most commonly caused by an upthrust of the ocean floor and massive release of energy following a large offshore earthquake, coastal landslip or island volcanic eruption.

Most tsunamis are small and go unnoticed. However, occasionally large tsunamis are generated and can be hugely destructive.

The first sign of a tsunami is often a rapid change in sea level or activity, which is then followed by the arrival of the first tsunami surge.

Local tsunami threats are those generated close to the New Zealand coast. For Hurunui these include large earthquakes off the Kaikoura/Marlborough/eastern North Island coast, or an underwater landslide into the Kaikoura canyon.

The threat from these sources is higher along the northern Hurunui coast than in Pegasus Bay.