They’re a regular and slightly unsettling feature of living in Wellington – those tremors that indicate the earth is on the move again.

They come without warning now that I’m no longer living with Frankie, the little Jack Russell, who used to start growling before the rest of us could feel the earthquake hit the city. Frankie was my early warning system.

Earthquakes occur on such a scale and so quickly that forewarning people of them is incredibly difficult even with the best technology. Tidal waves are easier – sensors at sea can detect the seismic shifts that cause them and send the alert to land, often minutes or hours before the waves roll ashore.

Any day now we may see one of New Zealand’s most sophisticated early warning systems in action. The Eastern Ruapehu Lahar Alarm Warning System on Mt. Ruapehu is designed to prevent anything like the disaster of Christmas Eve, 1953 when thousands of tonnes of water surged down the Whangaehu River taking out the Tangiwai railway bridge just before the Wellington to Auckland night express train arrived. Of the 285 people on board, 151 were killed when the train crashed into the swollen river.

How the multimillion dollar alert system works is laid out in the diagram opposite but it basically rests on an automated chain of communication designed to let the world know when the side of Mt. Ruapehu’s Crater Lake is about to give way.

Vibration and lake level sensors in the Crater Lake and a “trip wire” sensor maintained by the Department of Conservation and Genesis Power are constantly sending information via radio links to Genesis computers at the Tokanuu Power Station. If the data coming in meet certain thresholds suggesting the Crater Lake is about to give way, alerts are simultaneously sent to the Police Communications Centre, Tranzrail and DOC scientists.

The public can get the alert at exactly the same time if they sign up to an innovative text message service being offered by the Ruapehu District Council and technology partner OPTN. Mobile users just need to text OPTNLAHAR to 2678. The service has a one-off cost of 50c to join up and 50c again to deregister by texting OPTXLAHAR to the same number.

As well as the big alert of the “dam break”, the service will also send out updates in its aftermath. The system is based on the same text-message Tsunami alert service operated in Tauranga Western Bay, Manawatu, Wiamate and South Waikato.

As the public are alerted, the police will be coordinating emergency services and Tranzrail will activate the road barriers on State Highway 1 and State Highway 49 as well as on the railway line stopping all traffic into the path of the torrent of mud and water pouring into the Whangaehu River.

The scientists expect the probability of the Crater Lake giving way again is around 50 – 60 per cent and rising, so there’s a good chance we’ll get to see the early alert system in action. Let’s hope it works in practice.

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