A tsunami is a series of water waves caused by displacement of a large volume of water typically caused by earthquakes, volcanic activity, or landslides. Tsunamis have been called “tidal waves” because the surge and withdrawal may resemble rapidly rising or falling tides, but tsunamis are in no way caused by the tides. There is no tsunami season. It is important to note that a tsunami event can last for several hours and the first wave is often not the largest of the series.
All tsunami’s are potentially dangerous and can strike anywhere along the Hawaii coastline. Areas are at risk if they are less than 25 feet above sea level and within a mile of the shoreline. Drowning is the most common cause of death associated with a tsunami. The Tsunami waves and receding water are very destructive to structures in the run-up zone. Other hazards include flooding, contamination of drinking water, and fires from gas lines or ruptured tanks.
Hawaii is lucky enough to have a Civil Defense Siren. When you hear the siren, turn on your radio or television to any station and listen for emergency information and instructions.
Because a tsunami can happen at any time, it is important to be prepared. Basic emergency supplies should be kept on hand as response time may be limited if a tsunami is imminent. More information on tsunami safety and preparedness can be found here.
Tsunami Warning – A tsunami warning is issued when a tsunami with the potential to generate widespread inundation is imminent, expected, or occurring. Warnings alert the public that dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after initial arrival. Warnings alert emergency management officials to take action for the entire tsunami hazard zone. Appropriate actions to be taken by local officials may include the evacuation of low-lying coastal areas, and the repositioning of ships to deep waters when there is time to safely do so. Warnings may be updated, adjusted geographically, downgraded, or canceled based on updated information and analysis.
Tsunami Advisory – A tsunami advisory is issued when a tsunami with the potential to generate strong currents or waves dangerous to those in or very near the water is imminent, expected, or occurring. The threat may continue for several hours after initial arrival, but significant inundation is not expected for areas under an advisory. Appropriate actions to be taken by local officials may include closing beaches, evacuating harbors and marinas, and the repositioning of ships to deep waters when there is time to safely do so. Advisories may be updated, adjusted geographically, upgraded to a warning, or cancelled based on updated information and analysis.
Tsunami Watch – A tsunami watch is issued when a tsunami may later impact the watch area. The watch may be upgraded to a warning or advisory or canceled based on updated information and analysis. Emergency management officials and the public should prepare to take action.
Tsunami Information Statement – A tsunami information statement is issued when an earthquake or tsunami has occurred of interest to the message recipients. In most cases, information statements are issued to indicate there is no threat of a destructive basin-wide tsunami and to prevent unnecessary evacuations. Information statements for distant events requiring evaluation may be upgraded to a warning, advisory, or watch based on updated information and analysis.
A cancellation is issued after an evaluation of water-level data confirms that a destructive tsunami will not impact an area under a warning, advisory, watch, or that a tsunami has diminished to a level where additional damage is not expected.