A tsunami (pronounced sue-nahm-ee) is a series of travelling ocean waves caused by a sudden disturbance of the ocean floor – such as an underwater earthquake (when the sea floor quickly moves up or down), a rock slide, a volcanic eruption, or another high-energy event – that sets in motion a large mass of water that spreads outward in all directions.Tsunamis have an extremely long wavelength – the distance between the crest (top) of one wave and the crest of the next wave – of up to several hundred miles long and can travel across entire ocean basins away from the disturbance or source area. The time between two successive waves can also be very long, about an hour in deep water. Tsunamis are sometimes incorrectly called "tidal waves" but tsunamis are not caused by the tides. Tides are caused by the gravitational interactions between the Sun, Moon and Earth.
Preparing for a Tsunami
It’s important to be ready for a tsunami and to know the natural tsunami warning signs so you’re not caught unprepared. A tsunami can travel at more than 970 km/h (600 mph) in the open ocean. It can travel a long distance in only a few hours or less, sometimes surprising areas that are affected by the tsunami, so it’s important to know the Tsunami Safety Rules.
Be Tsunami Smart and know the natural signs
If you are on the coast and you:
FEEL a strong and long earthquake
SEE an unusual disappearance of water, or oncoming wall of water?
- Tsunami may be preceded by a rapid fall in sea level as the ocean recedes, exposing reefs, rocks, and fishes on the sea bottom.
- Tsunami often come ashore as a wall of water
HEAR the roar?
- Abnormal ocean activity, a wall of water, and
approaching tsunami create a loud “roaring”
sound similar to that of a train or jet aircraft.
- Don’t wait for official evacuation orders.
- Immediately leave low-lying coastal areas
- Move inland to higher ground
- RUN if you see a tsunami coming to higher ground or as far inland as possible
Some of the most important things you can do to prepare are:
- Know if your property is at risk – with the help of local authorities identify potentially vulnerable areas (especially low-lying coastal locations) and consider what could be affected including your home, businesses, work place and other critical facilities.
- Make plans – if you live or work in a low-lying coastal area make yourself familiar with the quickest way to retreat to high ground and have a well-prepared personal evacuation plan.Make sure all family members know the evacuation plan and take part in the local community processes for planning, preparedness, hazard mapping, evacuation planning and search and rescue. Agree on a close friend or relative that should be contacted if children cannot reach their parents and vice-versa.
- Be aware of your surroundings – identify concrete steel reinforced multi-storey buildings, at least three (3) storeys that can be used for vertical evacuation if necessary. If you’re close to or on the coast and the water recedes quickly and unexpectedly from a beach (this is called drawback), or there is an earthquake, move to high ground at once. Do not stay to see what happens. Some beaches have tsunami warning sirens, so do not ignore them. The first wave in a tsunami is often not the largest. If you experience one abnormally-huge wave, get to higher ground quickly as even larger waves could be coming soon.
- Stay connected – by listening to the radio for official updates and instructions. And have the telephone number for your Disaster Response Agency handy.
- Gather key supplies – including items such as flashlights, extra batteries, a portable, battery-operated radio, first aid kit and manual, emergency food and water, cash and credit cards
During a Tsunami
If a tsunami is occurring, you need to know the hazards you face and how to minimize those dangers. Some of the most important things you can do are:
- Make sure you’re in a safe place – if you are in a coastal low-lying location during a tsunami, it’s likely an unsafe area, so it’s important that you move to higher ground or as far inland as possible. Recommended safe areas are 30m (100ft) or higher above sea level or 3km (2miles) or more inland. Don’t wait for an official warning before evacuating; authorities may not have enough time to issue a tsunami warning.
- Be aware of your surroundings and know the natural signs – sometimes tsunami may occur without the initial pulling pack of the sea. In this case, a massive wall of water may be seen approaching land. If you are unable to move to higher ground, go to an upper floor (at least the 3rd storey) or roof of a concrete and reinforced building. As a last resort, climb a strong tree if trapped on low ground.
- React to your conditions – if you’re swept up by a tsunami, look for something to use as a raft and remember that a tsunami is not a single wave, but a series of waves that can come ashore for hours, with the first wave often not being the largest. If a tsunami Warning is issued NEVER go down to the beach to watch the waves come in
After a Tsunami
- Pay close attention – listen to local radio stations and obey advisories and official instructions given by local authorities.
- Stay safe – Do not enter into declared danger zones identified by local authorities and stay clear from collateral activity and await further instructions. Stay out of damaged buildings and return home only when the ALL CLEAR is given by the authorities.
- Get help if needed – seek necessary medical care at health centres or hospital and boil all drinking water until the Health Authorities have declared the water supply safe.
- Help out – assist your neighbours and search and rescue personnel. Share information and eyewitness accounts of your area where possible.