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Published: 2004-11-23 00:00:00

The threat of tsunami in the eastern Coromandel and Bay of Plenty is much higher than previously thought, a study has found.

The eastern coastline can expect a one metre tsunami every 80 years and a 2.5 metre wave every 320 years, this week’s Environment Waikato Environment Committee meeting heard. A joint investigation into tsunami hazard by Environment Waikato and Environment Bay of Plenty has found that the risk is high enough to rank it the highest regional risk for a locally generated tsunami and sixth for one generated elsewhere in the world.

Tsunami are a series of ocean waves generated by the sudden displacement of large volumes of water and caused by earthquakes or landslides, submarine volcanic eruptions or meteor impacts. The massive waves caused major damage and loss of life in Papua New Guinea in recent years.

Hazards Analyst Lamorna Cooper said the research identified tsunami activity in the previous 5000 years along the eastern coastline and pinpointed sites for additional research and field investigations. Core samples catalogued tsunami events, identified hot spots and the final stage would develop appropriate response, planning and management actions.

A hazard profile indicates there have been seven tsunami recorded in the past 85 years that have generated a wave height of up to a metre with five events since 1700, generating wave heights of one to three metres. There have been six events as far back as 3000 years with a wave height higher than five metres.

Local and regional sources include earthquakes and undersea volcanoes, landslides, regional fault activity in the Taupo volcanic zone, offshore volcanoes such as Mayor and White Island and pressure waves generated onshore by volcanic eruptions at Taupo or Mt Taranaki.

Areas most at risk include the open coast from Otama Beach to Port Charles and out to Great Mercury Island and Mercury Bay especially Whitianga.

Rob Bell from NIWA said a one to three metre wave would cause damage and inundate houses and was different from storm waves. They were very long waves which appeared to have the whole sea behind them, coming in over several minutes at 50-60km an hour.

Local and regionally-generated tsunami were more destructive than those from further away with a shorter response time – 30 to 60 minutes for a local event and up to three hours for a regional event.

Previously the risk had been considered relatively low and recurrence long but the research showed that the risk was similar to a one in 100 year flood in the Waikato.

Stage three of the study would consult with key local authorities, lifeline agencies and the CDEM Group to develop planning responses at Regional and local level, ensure relevant response and recovery agencies are updated on the risks and that emergency management and response mechanisms are strengthened. It would also produce management plans and implementation strategies for coastal communities most at risk and educate the public.