A tsunami is a series of fast travelling waves caused by a large disturbance in the sea or on the ocean floor, such as an earthquake, landslide, volcanic eruption or meteorite. The waves can be an hour apart, and can travel many thousands of kilometres across the oceans at great speeds of up to 800 kilometres per hour.
A tsunami may go unnoticed as it crosses deep oceans, but it loses speed and gains height when it reaches shallow water. Large waves up to 15 metres or more in height can come crashing onto the land.
Even small tsunami waves can be dangerous, causing unusually strong currents and unpredictable water flows near the shore. This means a threat to beach, harbour, estuary and small boat activities.
In the last 200 years, there have been at least 3 tsunami that were more than 10 metres high at the New Zealand coast. Māori mythology also speaks of large tsunami. Some were caused by distant earthquakes, some by underwater quakes not far off the coast.
Know the warning signs
There are three ‘types’ of tsunami – local, regional and distant. For a local source tsunami which could arrive in minutes, there won’t be time for an official warning. It is important to recognise the natural warning signs and act quickly.
Move immediately to the nearest high ground, or as far inland as you can if you are at the coast and experience any of the following:
Feel a strong earthquake that makes it hard to stand up, or a weak rolling earthquake that lasts a minute or more,
See a sudden rise or fall in sea level,
Hear loud and unusual noises from the sea.
With regional and distant tsunami, we will have more time and you will likely receive official and unofficial warnings. If you get a warning from friends and family, or from civil defence and emergency management services by text, sirens, radio, website, or other means, follow their instructions, and move to higher ground or as far inland as you can.