Study of tsunami threat to Bay of Plenty
9 February 2005
Study of tsunami threat to Bay of Plenty For immediate release: Wednesday 9 February 2005
Tsunamis pose more of a threat to the Bay of Plenty than previously thought.
A geological study of the region’s coastline has found traces of six major tsunami events over the past 4000 years, each five metres in height or more. Another 11 smaller tsunami have been officially recorded since 1840 alone.
Environment Bay of Plenty, in partnership with Environment Waikato, initiated research into the tsunami hazard just over two years ago. The councils wanted to understand more about the potential threat of tsunamis to help them with civil defence planning.
The first stage of the project, which involved studying sediment cores for signs of early tsunami activity, was made public last year. Environment Bay of Plenty senior resource planner, Stephen Lamb, presented the results of the project’s second stage to the strategic policy committee today (Tuesday 8 February).
Mr Lamb told the committee the second stage analysed the general nature of the threat to the Bay of Plenty and Coromandel. It linked the findings of geological work with more recent historical records. It also studied the origins of local tsunamis, their causes, and the types likely to have the most impact. The final stage, to be commissioned soon, will define the areas of the coastline most at risk and consider options for managing that risk.
Mr Lamb said the geophysical survey had found traces of four localised tsunami events and two others that had a wider than regional impact over the past 4000 years. The survey could only pick up tsunamis greater than five metres, “so these were obviously quite significant events”. Another 11, smaller tsunamis (less than three metres) are recorded in New Zealand’s official historical records, started in 1840.
“The results show we have no automatic exemption from the impact of tsunamis. They have occurred in the past and are likely to occur again,” Mr Lamb said. A review currently being carried out of tsunami return periods will help assess the level of future risk.
The report suggests the greatest risk to the Bay of Plenty is from tsunamis originating close to shore, such as from an eruption of Mayor Island or a fault movement in the offshore Taupo Volcanic Zone.
A tsunami of this type could reach the coast in 30 to 60 minutes. “It seems that local or near-shore events are the likely cause of the significant events found by the geological research. They are likely to be more destructive than those generated at a distance.”
Tsunamis originating from further afield for example, from a landslide in the underwater Hikurangi Trough 250 to 300 kilometres away, would take two to three hours to reach the coast. Events of distant origin, say from a South American earthquake, could take 12 hours.
Strategic policy chairman Bryan Riesterer said tsunamis were “at the forefront of people’s minds” because of the devastating Boxing Day event. The regional council was already working to address the issue through this project, he added. The final stage will give constructive data on how to mitigate such threats.