Long Waves at New Zealand Ports 

To retrieve details of long waves at a particular port, click on the name in the map below:

Long Waves

The long waves that can be extracted from 1-minute tide gauge data come in three categories:

• Far Infra Gravity (FIG) Waves are linked with groups of swell waves. Typically, they have periods of 5 to 15 minutes
• Rissaga Waves (also known as meteorological tsunami) are generated by low-pressure systems propagating rapidly over complex bathymetry. Typically, they have periods of 10 to 20 minutes.
• Tsunami are generated by earthquakes, submarine avalanches, or caldera (volcano). Their period can be anything from a few minutes to an hour.

Long waves of any type can also cause basins, embayments or harbours to oscillate at their natural frequency. This is called "seiche". For example, the main seiche period of Lyttelton Harbour is 11 minutes, so incoming long waves with this period are amplified within the harbour. Pegasus Bay has a seiche period of 3.4 hours and these waves can be seen in Lyttelton Harbour also, though this seiche is mainly driven by tides and storm surge.

Enquiries: Derek Goring
Mulgor Consulting Ltd
24 Brockworth Place
Riccarton, Christchurch
New Zealand
Phone: 64 3 343 5400
Fax: 64 3 343 5403
Email: d.goring[at]mulgor.co.nz