How likely is a large tsunami & how much warning would I have?

It’s impossible to predict the exact likelihood of a damaging tsunami.  Large tsunamis that flood land are rare, however they can (and do) happen sometimes.

The most likely tsunamis are those that won’t flood land, but can create strong currents in the ocean, river mouths and estuaries. They are expected to occur around once or twice a decade – maybe a handful of times in someone’s lifetime.

A tsunami capable of flooding very low lying coastal areas could be expected to occur perhaps once or twice in someone’s lifetime.

A very large tsunami that could flood areas further inland, such as Kaiapoi, is expected to occur maybe once every 500 years – so that is possible but unlikely in someone’s lifetime.

Distance-Source Tsunami

The most likely source for a tsunami, of any size, is expected from somewhere across the Pacific. All four significant historic tsunamis to affect Pegasus Bay have come from South America (1868, 1877, 1960 and 2010). In these events, we are likely to have 12 hours or more before it reaches us, which is enough time to evacuate people from coastal communities.

Local-Source Tsunami

There are faults in Pegasus Bay but the recurrence intervals are very long (thousands of years) and all known evidence suggests they are too small to create large tsunamis.  They may however flood very low lying areas of coast and could arrive within 30 minutes.

Other-Source Tsunami

A large earthquake on the Hikurangi or Kermadec subduction zone, off the north and east coasts of the North Island, could create a tsunami that could flood land and would reach Pegasus Bay in 1.5 to 3 hours. The recurrence intervals of these faults are not well known but are probably in the order of several hundred years.

Remember, if an earthquake is long or strong, get gone! Don’t wait for an official warning.

For more information about potential tsunami sources, please visit the ECan Website.