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 kilometers and these waves can travel at speeds of 1000 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 meters 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 150 m 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 tsunami 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.
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.
- Familiarize yourself with information about tsunami and the natural warnings signs, such as earthquakes, rumbling/ roaring sounds or sudden changes in the behavior 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. (http://www.bom.gov.au/info/tsunami/tsunami_info.shtml)
- If you visit coastal areas regularly, familiarize 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. Practice your Evacuation Plan with your household.
- Ensure that your Emergency Kit is up to date and that you and your family / household know where it is.
- Ensure that you have a battery-powered radio and spare batteries.
- If you live near the sea, ensure that your home has an electrical safety switch installed.
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 neighbors have received the advice also.
- If you are on land and instructed to evacuate, immediately move inland or to higher ground at least 10 meters above sea level, or, if possible, move at least 1km away from all beaches, harbors 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 multistory 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, photographs and pets.
- Keep listening to your local radio station for further information and instructions.
- Wait for the all-clear before returning to your home.
- If you are on a ship or boat at sea, move to deep water (open ocean).
- If you are on a boat or ship in a harbor or estuary or shallow water close to shore and there is sufficient time, return to land, secure your vessel and move to higher ground.
What should you NOT do when a Tsunami Warning is issued:
- DO NOT go towards the water to watch a tsunami:
- Tsunami 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.
What can you DO after a tsunami?
- 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.
- 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 neighbors who may require special assistance.
What should you NOT 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:
Queensland Health recommends that, where possible, water should be brought to a rolling boil for approximately one minute before being used for drinking, food preparation or making ice. This simple precautionary measure should ensure that any risk to public health attributable to a contaminated water supply is minimized.
- 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.