Over The Horizon

Tsunami in the Hauraki Gulf

The Coastal Marine Group at the University of Waikato is currently underway with a research project investigating tsunami behaviour in the Hauraki Gulf, looking to model the impacts of different kinds of tsunami on the Auckland coastline.

The project involves the numerical simulation of tsunamis in the Gulf produced by three mechanisms:

a teletsunami generated off the west coast of South America

Teletsunami are tsunami that are capable of causing damage after crossing ocean basins. Predicted tsunami characteristics are available at the edge of the New Zealand continental shelf for a series of scenarios modeled by the US Department of Commerce. These will be input into the Coastal Marine Group tsunami model.

a local tsunami generated by an earthqauke along the Kerepehi Fault in the Firth of Thames

Probable characteristics of such an earthquake will be provided by the Auckland Regional Council from their recent seismic hazard assessment.

a local tsunami generated by a phreatomagmatic eruption in the Auckland Volcanic Field

Phreatomagnetic eruptions occur where hot magma meets water, such as the Hauraki Gulf. The characteristics of the volcanic event will be provided by the Auckland Regional Council from a volcanic hazard assessment due to be completed in December.

The first stage of this project has been to transfer the tsunami numerical model from the university's mainframe computer to personal computers. A typical simulation now takes about five minutes to run on a PC, compared to the five days the original model took in 1982.

The main restriction on modeling is the generation of a suitable model grid. A commercial product, TRIGRID, was purchased which has greatly accelerated and improved this aspect of the tsunami modeling. This is being used to generate three grids: the Hauraki Gulf; the Sunda Straits in Indonesia; and Poverty Bay.

The interest in Indonesia stems from the student undertaking the project, Gegar Pratseya from the Tsunami Research Center, Coastal Engineering Laboratory, in Jakarta.

At present, the development of the Hauraki Gulf model grid is progressing well, but has been put on hold while Gegar is back in Indonesia. The main purpoise of his return to Indonesia is to obtain data for the Sunda Straits grid, and to participate in a physical model study of the 1883 Krakatau (Krakatoa) tsunami. The largest of these tsunami was over 35 metres high and killed thousands of people around the Straits of Sunda.

The data collected from the physical model will be used to calibrate the volcanic module of the tsunami model. This will give a greater degree of confidence to the Hauraki Gulf modeling.

The final product of this project is hoped to be a tsunami response assessment for every 500 metres of the Hauraki Gulf coastline. This can be improved to every 250 metres in areas of particular concern once they are identified.

Dr Willem de Lange, Waikato University