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SMC|Student Services|Emergency Preparedness|Tsunami

Tsunami

What is a tsunami?
A tsunami is a series of waves most commonly caused by an earthquake beneath the sea floor. As tsunamis enter shallow water near land, they increase in height and can cause great loss of life and property damage where they come ashore.
 
Recent research suggests that tsunamis have struck the Washington coast on a regular basis. They can occur at any time of the day or night, under any and all weather conditions, and in all seasons. Beaches open to the ocean, bay entrances, tidal flats, and coastal rivers are especially vulnerable to tsunamis.

What is the difference between a 'distant' tsunami and a 'local' tsunami?
When a tsunami has been generated by a distant earthquake, it will not reach the coast for several hours, and there is time to issue a warning. When a tsunami is generated by a strong offshore earthquake, its first waves would reach the outer coast minutes after the ground stops shaking. Feeling an earthquake could be your only warning!

How do I know when to evacuate?

If you feel the ground shake, evacuate inland or to high ground immediately! A wave as high as 20 feet could reach many coastal areas within 30 minutes of the quake. Remember - the first wave is often not the largest; successive waves may be spaced many minutes apart and continue to arrive for several hours. Return only after emergency officials say it is safe.
 
If you notice a sudden drop or rise in sea level, move to high ground or inland immediately.
If you are inside and hear a broadcast or NOAA Weather Radio alert; or if you are outside and hear an AHAB alert signal follow the instructions provided.


What do the alerts mean?

Tsunami Warning - A tsunami warning is issued when a potential tsunami with significant widespread inundation is imminent or expected. Warnings alert the public that widespread, dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after arrival of the initial wave. Warnings also alert emergency management officials to take action for the entire tsunami hazard zone.
 
Tsunami Watch - A tsunami advisory is issued due to the threat of a potential tsunami that may produce strong currents or waves dangerous to those in or near the water. Coastal regions historically prone to damage due to strong currents induced by tsunamis are at the greatest risk. The threat may continue for several hours after the arrival of the initial wave, but significant widespread inundation is not expected for areas under an advisory.
 
Tsunami Advisory - A tsunami watch is issued to alert emergency management officials and the public of an event that may later impact the watch area. The watch area may be upgraded to a warning or advisory — or canceled — based on updated information and analysis. The public should prepare to take action.
 
Tsunami Information Statement - A tsunami information statement is issued to inform emergency management officials and the public that an earthquake has occurred, or that a tsunami warning, watch or advisory has been issued for another section of the ocean. In most cases, information statements are issued to indicate there is no threat of a destructive tsunami and to prevent unnecessary evacuations as the earthquake may have been felt in coastal areas.