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What is a tsunami

A tsunami is a series of long and wide ocean waves, caused by large-scale disturbances of the ocean, such as earthquakes, landslide, volcanic eruptions, explosions and meteorites.

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What is a tsunami

Tsunami are a series of long and wide ocean waves (like a ripple effect), caused by large-scale disturbances of the ocean, such as earthquakes, landslide, volcanic eruptions, explosions, or meteorites.

Tsunami waves travel fast across oceans, generally with little impact. It is when these waves approach shallow and coastal areas they slow down and increase in height. Being wide and long series of waves, there is a large volume of water behind each wave. Unlike normal ocean waves, which roll and break quickly, tsunami waves can roll onto shore and continue inland, for long periods of time. Sometimes it is not the first tsunami wave which is the largest. The ripple effect of tsunami waves impacting coastal areas can often be exaggerated in areas like harbours, where these ripples can bounce around in more closed water areas linked to the ocean.

Tsunamis can be classified as either local, regional, or distant, depending on the distance of generation from the coastline.

NSW SES tsunami warnings

The NSW SES will issue tsunami information through the Australian Warning System, including Advice and Emergency Warnings. 

Advice

An incident has started. Stay up to date in case the situation changes.

  • Stay informed
  • Monitor conditions
  • Reduced threat - Return with caution
Emergency Warning

The highest level of warning. You may be in danger and need to take action immediately.

  • Evacuate now/before
  • Avoid the area

The natural warning signs of tsunami

In Australia you may receive an official Tsunami Warning,  however it is also important to be aware of the natural warning signs.

You may:

  • FEEL the earth shake. If you are near the ocean and you feel the ground shake, a strong earthquake may have occurred and possibly caused a tsunami. However, you may not feel the earth shake if the earthquake occurred long way away.
  • SEE the ocean drop. Before a tsunami arrives, the ocean level may (but not always) drop dramatically before returning as a wall of water. If you notice that the water is disappearing, tell your family and friends and  prepare to move to higher ground.
  • HEAR an unusual roaring sound. If you hear a loud roaring sound from the ocean (a bit like an aeroplane or a  train), tell your family and friends. This sound may be heard before a tsunami arrives.

JATWC tsunami warnings

Official Tsunami Watches, Tsunami Warnings, No Threat Bulletins and Tsunami Cancellations and Tsunami Warning Summaries are issued by the Joint Australian Tsunami Warning Centre.

Tsunami Warnings will indicate a threat level that indicates whether tsunami are likely to:

  • Affect the marine and immediate foreshore
  • Cause land inundation of low lying coastal areas, or
  • Pose no threat to an area

About Tsunami Watches, Warnings, No Threat Bulletins, Cancellations and Warning Summaries

No Threat Bulletin

To advise people that the earthquake has been assessed and that no tsunami threat exists.

In the first stage seismologists determine that there is the potential for an identified undersea earthquake to cause a tsunami threat to Australia. If there is no threat, a National Tsunami No Threat Bulletin will be issued.

Tsunami Watch

To advise people that a tsunami threat may exist and that they should look out for further updates. 

In the first stage seismologists determine that there is the potential for an identified undersea earthquake to cause a tsunami threat to Australia. If there is a threat, the Bureau will issue a National Tsunami Watch.

Tsunami Warning

To advise people that a tsunami threat does exist and to advise them of the level of threat and action they should take.

If sea level observations and further data confirm the tsunami threat, or if any potential first point of impact is less than 90 minutes away, the Bureau, on behalf of the JATWC, will use its severe weather communication infrastructure to issue Tsunami Warnings for the States and Territories under threat.

Tsunami Warning Cancellation

When the main threat has passed or if a tsunami didn't eventuate, the Bureau will issue a Tsunami Watch Cancellation or Tsunami Warning Cancellation. The relevant State or Territory emergency authority will inform the public when it is safe to return to the affected area.

National Tsunami Warning Summary

To provide the public, media and emergency authorities with the status of tsunami warnings nationally.

Official Tsunami Watches, Tsunami Warnings, No Threat Bulletins and Tsunami Cancellations and Tsunami Warning Summaries are issued by the Joint Australian Tsunami Warning Centre.

Tsunami Warnings will indicate a threat level that indicates whether tsunami are likely to:

  • Affect the marine and immediate foreshore
  • Cause land inundation of low lying coastal areas, or
  • Pose no threat to an area

Threat levels

Tsunami Warnings are broken into 3 different threat levels:

No threat

An undersea earthquake has been detected, however it has not generated a tsunami, or the tsunami poses no threat to Australia and its offshore territories.

Marine and immediate foreshore threat

Warning of potentially dangerous rips, waves and strong ocean currents in the marine environment and the possibility of only some localised overflow onto the immediate foreshore.

Land inundation threat

Warning for low-lying coastal areas of major land inundation, and flooding, dangerous rips, waves and strong ocean currents in the marine environment.