What is a tsunami?
A tsunami is a series of fast moving waves produced during large scale ocean disturbances. A tsunami can occur with very little warning; caused by a variety of natural or technological events, such as earthquakes, volcanic eruptions, explosions, landslides, and meteorite impacts.
A tsunami is different from regular ocean waves in several ways:
- A tsunami is a series of sea waves that are extremely long. As a tsunami crosses a deep ocean the length from crest to crest may be as much as 150 kilometres and these waves can travel at speeds of 1,000 km/h.
- As a tsunami leaves the deep water of the ocean and travels to the shallower water near the coast, the tsunami slows and the wave height increases. This process is called shoaling.
- A tsunami that is unnoticeable at sea, because of its long wave lengths, may reach several metres or more in height by the time that it reaches the coast.
- Regular ocean waves move in the water from the surface down to around 150m deep, but a tsunami moves in the water all the way to the seafloor. Therefore the volume of water that is moved by a tsunami is significantly more than the amount moved by regular ocean waves.
- As many tsunamis are a series of waves, there is often more than one wave and the first wave may not be the largest.
- Depending on whether the first part of a tsunami to reach the shore is a crest or a trough, it may appear as a rapidly rising or falling tide.
- Even a small tsunami can be very dangerous to swimmers and mariners.
Because of the limited warning time for a tsunami, it is very important for you to plan and prepare your family or household for a tsunami in advance.
What can you do to prepare for a tsunami?
- Contact your local council to find out about the risk of tsunami in your community.
- Familiarise yourself with information about tsunami and the natural warnings signs, such as earthquakes, rumbling/roaring sounds or sudden changes in the behaviour of coastal seas (the sea level may recede dramatically).
- Visit the Bureau of Meteorology website for more information. The Bureau of Meteorology has the overall responsibility for issuing Tsunami Warnings in Australia.
- If you visit coastal areas regularly, familiarise yourself with the tsunami history of these areas and identify the areas that may be prone to flooding.
- Develop an Evacuation Plan with your family or household. Identify the nearest high ground and the safest routes to it. Practise your Evacuation Plan with your household.
- Ensure that your Emergency Kit is up to date and that you and your family or household know where it is.
- Ensure your home has an electrical safety switch installed.
- Check your home and contents insurance policy – does it cover you for storm surge, cyclone and flooding? Does it include clean-up and debris removal?
- Develop an Emergency Plan for your vessel that includes information on where to moor your boat quickly and safely, should a Tsunami Warning be issued.
- If it is safer to move to the deep ocean, you should also be familiar with the boating requirements of the area you are operating in, local dangers, special rules and regulations.
- Know where and how to safely move out to deep ocean, how long it takes and how to get back safely to the harbour or port.
How you will be advised of a Tsunami Warning?
In Australia, the Joint Australian Tsunami Warning Centre (JATWC) is jointly operated by the Bureau of Meteorology and Geoscience Australia. The JATWC detects and verifies any tsunami threat to the coastline of Australia and its offshore territories.
Warnings will be relayed through Emergency Authorities via official channels (eg Emergency Alert, radio, television, sign boards and the internet), Lifeguards, Surf Lifesavers and/or unofficial channels (eg face to face or verbal announcement).
Depending on the level of threat determined by the JATWC, the Bureau of Meteorology may issue a Tsunami Warning restricted to the marine environment and immediate foreshore area for parts of the Australian coastline. Tune into warnings via Emergency Alert, the radio, television, ‘1300 TSUNAMI’ (1300 878 6264) or the Bureau of Meteorology’s website.
What is the different between marine and land Tsunami Warnings?
- A warning of potentially dangerous waves, strong ocean currents in the marine environment and the possibility of only some localised overflow on to the immediate foreshore.
- A warning for low-lying coastal areas of major land inundation, flooding dangerous waves and strong ocean currents.
- Local emergency authorities may order evacuations of high risk areas.
What should you do when a Tsunami Warning is issued?
- Listen to your local radio station for information and instructions.
- Listen carefully to the warning and act immediately on the advice provided. Check that your neighbours have also received the advice.
- To help minimise the risk to your safety; it is important to follow the advice contained in these warnings.
Land inundation threat
- If you are on land and instructed to evacuate; immediately move inland or to higher ground at least 10 metres above sea level or, if possible, move at least 1km away from all beaches, harbours and coastal estuaries/riverbank areas.
- It will be in your own interests to walk to safety if possible to avoid traffic jams.
- If you are unable to leave the area, take shelter in the upper level of a sturdy brick or concrete multi‑storey building and stay there until advised that it is safe to leave (homes and small buildings are not designed to withstand tsunami forces).
- Make the following preparations if you are advised to evacuate:
- Lock your home and follow recommended evacuation routes for your area.
- Take your emergency kit with you, as well as important papers, medical needs, pets and photographs.
Marine and immediate foreshore threat
- Get out of the water and move away from the immediate water’s edge of harbours, coastal estuaries, rock platforms and beaches.
- If you are on a boat or ship in a harbour or estuary or shallow water close to shore and there is sufficient time, return to land, secure your vessel and move to higher ground. (Refer also to land inundation threat information, above).
- If you are on a ship or boat at sea, move to deep water (open ocean) well off‑shore and remain there until further advised.
- Do not go to the coast or headlands to watch the tsunami.
- Check that your neighbours have received this advice.
- Keep listening to your local radio station and media for further information and follow the advice from emergency services.
- Wait for the all-clear before returning to your home or to port.
What NOT to do when a Tsunami Warning is issued?
- DO NOT go towards the water and or to a headland to watch a tsunami.
- Tsunamis move significantly faster than normal wind-driven waves and can move faster than people can run.
- Once you see the tsunami it is too late to escape.
- The backwash of a tsunami is extremely dangerous. As the large volume of water recedes back towards the ocean, it may carry debris and people back to sea with it.
- DO NOT enter the water:
- Even a small tsunami causes strong turbulence and very dangerous currents.
- DO NOT drive through water of unknown depth and current.
- DO NOT return to coastal areas/low lying areas until an all-clear is given by emergency services or public officials.
- DO NOT return to port if you are on a ship or boat until advised that it is safe to do so:
- Damaging wave activity and unpredictable currents can affect harbours for some time after the initial tsunami impact.
How will I know that the tsunami threat is over?
- Tsunami Warnings will be cancelled by the Joint Australian Tsunami Warning Centre when the main threat is deemed to have passed.
- Emergency authorities will inform the public when it is safe to return to the affected area. This advice will be related through emergency authorities via official channels, such as radio, television, signboards or via the internet, ‘1300 TSUNAMI’ (1300 878 6264) or the Bureau of Meteorology’s website www.bom.gov.au/tsunami.
- Caution should continue to be exercised. Strong waves, current and abnormal sea levels may still affect some beaches, harbours and coastal waterways for hours, or even days after, depending on the location.
What NOT to do after a tsunami?
- DO NOT go near flooded and damaged areas until the emergency services or public officials advise that it is safe to return.
- DO NOT drink unboiled tap water until water supplies have been declared safe.
- DO NOT eat food which has been immersed in flood waters.
- DO NOT use gas or electrical appliances which have been immersed in flood waters until they have been checked and declared safe.
What can you DO after a tsunami?
- When you are advised that you may return to areas impacted by tsunami, enter buildings with caution. Check for damage to gas fittings, electrical fittings, sewerage and water systems.
- Help injured or trapped persons where possible and remember to keep yourself safe from injury when providing assistance.
- Call Triple Zero for Ambulance, Fire and Rescue and Police in an emergency.
- Remember to check on your neighbours who may require special assistance.