Potential Tsunami Sources

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.

Distance Source Tsunami

A distant source tsunami is a tsunami that takes more than three hours to reach the coast from its source.

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).

A distant source earthquake would not be felt along the Pegasus Bay coast, but there would be enough time to issue an official warning and, if the tsunami was coming from across the Pacific Ocean with a 12+ hour travel time, undertake a managed evacuation.

Regional Source Tsunami

A regional source tsunami is a tsunami that takes between one and three hours to reach the coast from its source.

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.

There would likely be time to issue an official warning before the first tsunami waves arrive, but the long earthquake should be people’s cue to evacuate because the official warning may not effectively reach everyone in time.

Local Source Tsunami

A local source tsunami is generated close to shore, usually by an underwater earthquake or

landslide, which takes less than one hour to reach the coast.

The likelihood of a damaging local source tsunami being generated off the Pegasus Bay coast is thought to be relatively low and the most likely effect if it did occur would be strong and unpredictable currents and surges in the water, and inundation of very low-lying land, depending on the tide stage.

There would not be time to issue an official warning before the first tsunami waves would be due to arrive.

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.