Tsunami

What are tsunami?
What are the risks from tsunami?
Have tsunami impacted Northland in the past?
What is at risk in Northland?
What are we doing about it?
What have we done so far?
What else is planned?
Northland Regional Council commissioned reports
Other useful resources

What are tsunami?

Tsunami are long period waves, most often generated by displacement of the sea floor associated with earthquakes, volcanic eruptions or landslides.

Tsunami can cause devastation to coastal communities with potential for destruction of coastal infrastructure, property and loss of life from the powerful waves and their inundation of land.

Damage from a tsunami to a store at Ahipara. Damage from tsunami of unknown source to Berghan Family Store at Ahipara circa 1916 (Image: Far North Regional Museum).

What are the risks from tsunami?

Risk from tsunami in New Zealand is significant due to our exposure to significant tsunami-generating sources from the Pacific ‘Ring of Fire’ and our increasing amount of coastal development.

The amount of damage from tsunami is estimated to be about twice of what is expected from an earthquake event with a similar return period, with deaths and injuries likely to be many time more.

Have tsunami impacted Northland in the past?

A number of moderate-to-large tsunami have impacted Northland's coast, both historically and prehistorically, as recorded in oral traditions, written accounts and geological evidence.

In last 150 years, four moderate-to-large tsunami events have impacted Northland’s east coast.

Pre-historically, one large event, or a series of large, closely-spaced events, occurred around 600 years ago, along with other events around 3000 and 6500 years ago.

There are also likely to be other past tsunami events that have not been recorded or detected from geological evidence.

Aerial view of Taipa. One of several historic accounts (from F.Keene's book ‘To The Northward’ (1977), of how Taipa, located in Doubtless Bay, was named is “...many years ago a great tidal wave washed right over the pa on the seashore, temporarily submerging it. After the excitement of this catastrophe had died down, the survivors called the place Taipa (tai, sea-water; pa, village)”.

What is at risk in Northland?

Moderate-to-large historical tsunami events that impacted Northland occurred when development on the coast was modest, in comparison to today.

Significant coastal development since the last moderate historic event means there is now increased exposure to risk from tsunami hazard.

Any coastal-sited development or infrastructure, or coastal property is potentially at risk from tsunami, including in Northland, which has:

over 30 coastal settlements;
infrastructure such as water supply, sewage, power, telecoms, road and rail;
over 1600 coastal structures, 3000 moorings, 130 marine farms and 7 marinas; and
coastal-sited industry and port infrastructure.

Above: Rapidly developing coast. Both images are of the same area of Ahipara, north of Wairoa Stream, showing the extent of development from 1950 (left) to 2004 (right).

What are we doing about it?

The Northland Regional Council has been working with scientists, planners and stakeholders to better understand the risk from tsunami to Northland, to enable us to better prepare for and manage the risk from tsunami hazard.

What have we done so far?

Review of prehistoric and historic tsunami record

Marine cobbles located on the dune up to 30m above MSL at Tom Bowling Bay, Far North, deposited from prehistoric tsunami of unknown origin.

Northland's tsunami record was assessed by reviewing the literature, geological data - including sediment coring for assessment of prehistoric tsunami deposits - and a field reconnaissance of the Northland coast.

REPORTS:

Pearce, S. (2006) Sedimentary record of palaeotsunami from two backbarrier wetlands, east coast Northland. Unpublished MSc thesis, University of Auckland, SGES, 115pp.

Chagué-Goff, C.; Goff, J. R. (2006). Tsunami hazard assessment for the Northland region. NIWA Client Report CHC2006-069.

Newspaper article following the 1960 tsunami generated from the Chile (C/- Northern Advocate).

Newspaper article following the 1960 tsunami generated from the Chile (Source: Northern Advocate).

Identification of tsunami generating sources

The most significant tsunami-generating sources were identified and risk assessed through a review of the literature and numerical modelling.

REPORT

Goff, J.; Walters, R.A.; Callaghan, F. (2006). Tsunami source study. NIWA Client Report CHC2006-082. Report for Environment Waikato (on behalf of Environment Waikato, Auckland Regional Council, Environment Bay of Plenty, Northland Regional Council). 55 p.

Maximum water surface elevations for an L: eastern distant source tsunami (Chile)

Eastern regional/local source (Tonga- Kermadec Mw9.0).

Numerical modeling of tsunami wave height at coast.

Several tsunami event scenarios were modelled for the Northland coast. The outputs from this work included wave height at coast, onshore current speed and wave arrival times. Tsunami inundation modelling was also completed for Ahipara and Taipa for several tsunami event scenarios.

REPORT

Lane, E.; Walters, R. A.; Arnold, J.; Roulston, H. (2007). Northland Regional Council Tsunami Modelling Study 1. NIWA Client Report: CHC2007-109. Report for Norhtland Regional Council. 88 p.

Obtaining Accurate Land Surface Information

To be able to model the way tsunami waves inundate land it is necessary to have accurate information on the surface of the land. To do this we obtained high resolution LiDAR topographic data for approximately 30 coastal communities in Northland for land that was generally below 20 metres elevation.

This data is used to create a land surface model which is used in the numerical model to represent that land surface.

Langs Beach L: Aerial image R: LiDAR composite image demonstrating elevations and high resolution of data.

What else is planned?

Numerical modelling of tsunami inundation at coastal settlements.

We are currently working with scientists to assess risk to approximately 30 coastal settlements through tsunami inundation modelling.

To achieve this we are applying our knowledge from previous work to a numerical model and accurate land surface data (LiDAR) for several tsunami event scenarios to assess:

landward extent and water depth of tsunami inundation over land;
maximum current speeds from inundation over land;
wave arrival times; and
animations of inundation for some areas.

This work is planned in two phases, which are due for completion in June 2008 and June 2009.

Inundation model results for Taipa for an eastern regional/local source scenario (Tonga- Kermadec Mw9.0) Left: Inundation extent and depths Right: Maximum current speed.

How will we use the information?

The information will primarily be used to increase preparedness for tsunami hazard through such mechanisms as:

landuse planning (i.e. development plans, hazard identification maps);
evacuation route planning and mapping;
notice boards; and
education and awareness.

What can I do to help prepare?

Consult with your local authorities and civil defence representatives to understand and better prepare for tsunami hazard - and get involved with your local community.