Natural hazards and emergencies

Tsunami

A tsunami is a series of waves created by the sudden movement of the ocean floor caused by earthquakes or underwater landslides or volcanic eruptions. In deep water a tsunami therefore can travel at more than 500km/h at great distances in just hours. 

In the ocean, tsunami are generally small. When they enter shallow water, they increase in height and travel more slowly. Tsunami have been known to reach 10m and more in height. Typically, they have wave periods of 15 to 60 minutes, much longer than wind waves or swell.

 


Tsunami sources

Local, regional or distant sources can generate a tsunami. Sources that could create a tsunami in Auckland include:

  • Local - Offshore faults, underwater volcanic eruption, large underwater landslides.
  • Regional - Tonga-Kermadec Trench, Southern New Hebrides Trench, large earthquakes near the southwest Pacific islands.
  • Distant - Any location around the Pacific Rim including, South America, Alaska, the Aluetian Islands, Kamchatka, Japan.

The size and nature of any tsunami affecting Auckland will vary on the source location and how it was created. 

Here are examples of tsunami observed here:

Year

Located Observed

Wave height (m)

Source

Cause

1868

Great Barrier Island
Tamaki Estuary
Orewa
Port Charles

2.90
1.50
1.80
1.80 

Chile

Earthquake

1877

Auckland
Thames
Port Charles

0.20
0.90
3.60 

Chile

Earthquake

1883

Auckland
Thames
Coromandel

1.80
1.50
0.90 

Krakatau Volcano

Volcanic eruption 

1952

Auckland

0.10

Kamchatka, Russia

Earthquake

1960

Great Barrier Island
Auckland 

1.50
0.60

Chile

Earthquake

1964

Auckland

0.45

Alaska, USA

Earthquake

1976

Auckland

0.10

Kermadec Islands

Earthquake

1977

Auckland

0.10 

Kermadec Ridge

Earthquake

1982

Auckland

0.10

Kermadec Islands

Earthquake

1986

Auckland

0.10

Kermadec Islands

Earthquake

1993

Auckland

0.10

Kermadec Islands

Earthquake

1994

Auckland

0.10

Kuril Islands

Earthquake

2007

Aniwhata

0.12

New Georgia Islands

Earthquake

2009

Auckland

<0.5m

Samoa

Earthquake

2010

Auckland

<1.0m

Chile

Earthquake

2011

Auckland

<0.5m

Japan

Earthquake

 


Local source tsunami in Auckland

There is a low likelihood of a local source tsunami affecting Auckland, If one did, the effects would be significant due to the limited warning time - less than one hour. 

Auckland is one of the lowest seismically active parts of New Zealand. While large earthquakes aren’t common, the chance of a large tsunami-generating earthquake is possible. The Kerepehi Fault, in the Firth of the Thames, is possibly active offshore and could generate earthquakes up to magnitude 7.1.  Research suggests this fault does not represent a major tsunami threat to Auckland. 

An underwater volcanic eruption in the Hauraki Gulf or harbours surrounding Auckland could create a local source tsunami. If magma from a volcano suddenly comes into contact with water it can generate an explosive eruption called a phreatomagmatic eruption which can send large waves towards shore.

 


Regional source tsunami in Auckland

Regional source tsunami are created in locations where the wave will come ashore one to three hours after generated. The most common source is subduction zones, where tectonic plates collide. The most common source concerns those in the southwest Pacific.
 
The Tonga-Kermadec trench to the east and northeast of Auckland could generate earthquakes greater than magnitude 9.0. Auckland Council has modelled the effects. The most susceptible to tsunami are coastal communities in the north. Coast wave heights for other parts of Auckland vary considerably.

This modelling shows maximum coast wave heights for selected Auckland communities for 100 large earthquakes on the Tonga Kermadec Trench.

Location

Maximum modelled at coast wave height (metres)

Omaha

6.2

Orewa

2.8

Whangaparaoa

1.5

Takapuna

2.1

Northcote

0.9

Point Chevalier

0.5

CBD

0.9

Tamaki River

1.0

Howick

0.8

Beachlands

0.7

Oneroa

2.3

Onetangi

2.7


The South New Hebrides Trench, Vanuatu and Samoa are among areas in the southwest Pacific that could generate tsunami to New Zealand. Travel time to Auckland would be 2 to 3 hours.

 


 

Distant source tsunami in Auckland

Distant source tsunami generally have travel times between three and 15 hours. Large earthquakes occurring anywhere around the Pacific Rim have the potential to generate tsunami that can affect Auckland. Distant source tsunami from Alaska, Russia and most commonly South America have all been observed in Auckland.

The most frequent distant source of tsunamis affecting Auckland is the west coast of South America. Tsunami generated here generally take around 12 to 15 hours to arrive and can affect both coasts, depending on the size and location of the earthquake. In August 1868, a large earthquake generated a tsunami that took 15 hours to reach Auckland and reached up to 2.9m on Great Barrier Island’s east coast. In May 1960, the largest earthquake ever recorded, magnitude 9.5, occurred in Chile and created a tsunami that reached 1.5m on Great Barrier Island.

The Krakatau volcanic eruption of May 1883 in Indonesia generated a tsunami of about 1.8m in Auckland. This event was rare as it is one of only a few tsunami to occur in Auckland not created by earthquakes.

 


 

More information

The GNS Science website, through the GeoNet Project, monitors the arrival of tsunami in New Zealand. 

The United States National Oceanic and Atmospheric Administration (NOAA) website maintains and operates deep ocean buoys that provide some warning of a tsunami being generated. 

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