Watching out for massive waves (tsunamis)

Many coastal communities around the globe live with the risk of a devastating tsunami. The tragic Boxing Day Tsunami of 2004, with a death toll of over one million, highlights the extreme effects on people, property and the environment that a tsunami can have. In New Zealand we have experienced about 10 tsunamis higher than five metres since 1840, most of them caused by seafloor quakes or collapsing banks of sediment off the edge of the continental shelf.

In May 2008, technicians and scientists from Land Information New Zealand (LINZ) and GNS Science finished installing the fifth sea-level gauge at the Port of Tauranga in a planned network of 20 gauges around New Zealand. It is a big job installing all the gauges and the technicians won’t be finished until 2010. This national network of gauges will be for monitoring tsunamis. Five gauges will be on offshore islands, with the rest at coastal locations.

The gauge in Tauranga is attached to an underwater pile on the tug boat berth. Sensors inside the gauge measure changes in water pressure which relate directly to the wave height above the instruments.

The gauges at coastal locations such as Tauranga will detect first landfall of tsunami waves. They will also enable an ‘all-clear’ to be given if a large undersea earthquake has not produced a tsunami, or if a near-shore earthquake has generated only a small wave.

The instruments on offshore islands such as Raoul, Macquarie and Norfolk will give information about the size and possible arrival times of incoming tsunamis from distant sources.

Instruments in the network send continuous data by radio to GNS Science in Lower Hutt. In the event of a tsunami reaching the coast, information from the network will be provided promptly to New Zealand civil defence agencies so they can focus their response on areas that have been affected most.

A scientist working on the project, Dr Ken Gledhill, said the sea-level measuring network is important to the tsunami monitoring system which uses seismology, sea-level measurements, computer modelling and historical information on seafloor earthquakes.

The information the network records will be shared in real time with tsunami warning centres around the Pacific.