Prepare by understanding the tsunami hazard

What is a tsunami?

Tsunami are waves caused by sudden movement of the ocean surface due to earthquakes, landslides on the sea floor, land slumping into the ocean, large volcanic eruptions or meteorite impact in the ocean. Tsunami hazard is more commonly associated with large earthquakes that primarily occur in under-sea subduction zones or faults (see: https://youtu.be/ILlyfwDwJVs ).

A tsunami is often a series of waves and the first may not necessarily have the greatest amplitude. In the open ocean, even the largest tsunami are relatively small, with wave heights typically tens of centimetres or less away from the initial tsunami generation zone.

For more information on tsunami hazard go to: https://www.ga.gov.au/scientific-topics/community-safety/tsunami

Tsunami Hazard in Tasmania?

Whilst Tasmania has not been significantly impacted by a tsunami in its recent history, its proximity to under-sea subduction zones that stretch from Papua New Guinea to New Zealand and into the Southern Ocean (south of New Zealand), give rise to the potential for tsunami activity, particularly along the southeast and east coasts of Tasmania.

There are three broad types of tsunami threat that may have different consequences within Tasmania:

No Threat Tsunami: These tsunami cause tidal variations, local currents and unusual tidal flows, but are not expected to provide a significant threat to either the marine environment or the land environment.  In Tasmania, these tsunami are relatively common.  Recent examples of these tsunami and their impact on Tasmania are:

2004 – Indonesia magnitude 9.0 quake caused 0.6m tsunami on east coast.
2007 – Puysegur Trench magnitude 7.4 quake caused 0.35m tsunami on east coast
2009 – Puysegur magnitude 7.9 quake caused 0.55m tsunami at Southport
2010 – Chile magnitude 8.8 quake caused 0.28m tsunami at Southport
2011 – Japan magnitude 9.0 quake caused 0.23m tsunami at Spring Bay

Marine Threat Tsunami: These tsunami potentially cause dangerous rips, strong currents and waves within the marine environment and the possibility of only some localised overflow into the immediate foreshore.  These could be quite hazardous to vessels in shallow water, particularly at marinas, or swimmers in beach environments.  Marine Threat tsunami could occur in Tasmania every 10 to 20 years.

Land Threat Tsunami:  These tsunami are expected to inundate low lying coastal areas of Tasmania to a depth ranging from 0.1m to 3m, with a run-up to 10m elevation from sea level for a worst case tsunami.  They will also cause dangerous rips, waves, turbulence and strong ocean currents.  Palaeo-tsunami research indicates that Tasmania has experienced significant land threat tsunami 2-4,000 years ago.  While very rare, the consequences could be catastrophic.

To support tsunami emergency planning, worst case tsunami inundation modelling, based on a 1:13,000 recurrence interval tsunami event at Highest Astronomical Tide, has been conducted by Mineral Resources Tasmania (MRT) to inform the areas that may need evacuation and to inform measures for shipping safety in Hobart Port during a Land Threat Tsunami warning.  For more information on this research see the Technical Report on Tsunami Modelling in South East Tasmania February 2018. To learn more about this research, contact MRT, Claire Kain (Natural Hazards Geologist) on 03 6165 4742.

This research confirms that areas at risk from a Land Threat Tsunami will extend inland up to an elevation of 10m above sea level, or, for low lying coastal land below 10m elevation, up to one kilometer inland.  These areas will be considered to be at risk during a land threat tsunami and may require evacuation to higher ground.

Other Preparations

You can also take these steps to be prepared:

• If you live on or regularly visit the coast, learn as much as you can about hazards that may affect you.
• Know the nearest high ground (more than 10 metres above sea level for land threat tsunami) and the safest way to get there. High ground may include the second story of a sturdy building.
• Keep your family emergency kit up to date and know where it is.
• Take notice of natural warnings of an impending land threat tsunami – earthquake, rumbling or sudden changes in sea behaviour.
• Maintain a Home Emergency Plan

Tsunami Warning

The Joint Australian Tsunami Warning Centre (JATWC) is the tsunami warning authority for Australia.  Should there be a known tsunami threat to Tasmania, the JATWC will issue a Marine Threat Warning or a Land Threat Warning through the Bureau of Meteorology.

These warnings are made publicly to media and broadcasters, and also to Tasmania Police and the State Emergency Service who will take action according to the State Tsunami Emergency Response Plan.  For further details on the tsunami warning system go to: http://www.bom.gov.au/tsunami/about/tsunami_warnings.shtml

What to do if a tsunami warning affects you?

No Threat Tsunami: No action should be necessary

Marine Threat Tsunami:

• Monitor local TV or radio to assess the potential hazard within your immediate marine environment. Circumstances with tsunami hazard can easily change based on the state of tide, storm surge and other factors.
• If you are in the water, or on the water front on a beach or rocks, move off the beach/rocks and away from estuaries.
• If in a vessel, secure it to a berth and move away from the waterfront. Stay clear of marinas. If at sea, remain in deep water until the hazard has passed (remember, tsunami arrive on the coast as a series of waves, the first may not be the largest)

Land Threat Tsunami: 

• Monitor local TV and radio closely.
• Follow the instructions of emergency services and local officials.
• If you are within 10 metres elevation from sea level, move immediately to higher ground until authorities give the all clear to return. Remember, a tsunami is a series of waves – there will be more than one wave and the first may not be the largest.
• If you cannot reach high ground, shelter in the upper floor of the closest sturdy building and stay there until advised that it is safe to leave.
• NEVER go onto the beach, a breakwater, estuary or harbour to watch a tsunami. Stay away from the water’s edge. A tsunami can move faster than people run.
• If you’re on a ship or boat at sea, move to deep water (at least 25 metres). Do not return to port until advised it is safe to do so. Damaging wave activity and unpredictable currents can affect harbours for a period of time after the initial tsunami impact.
• If you are on a ship or boat in shallow water close to shore and there is sufficient time, return to land and secure your boat before seeking high ground.
• NEVER return to low lying areas unless you have been told it is safe to do so by emergency services or public officials