The phenomenon we call a "tsunami" is a series of traveling ocean waves of extremely long length and period, generated by disturbances associated primarily with earthquakes occurring below or near the ocean floor. Underwater volcanic eruptions and landslides can also generate tsunamis, although these sources are significantly less frequent.
As the tsunami crosses the deep ocean, its length from crest to crest may be 124 miles or more and its period 15 minutes to an hour, but its height from trough to crest may only be a few inches, even for a very destructive tsunami, it cannot be felt aboard ships in deep water. As the tsunami enters shallow water near coastlines in its path, the velocity of its waves decreases and its wave height increases.
It is in these shallow waters that tsunamis become a threat to life and property because they can crest to heights of more than 30 feet, strike with devastating force, and flood low-lying coastal areas. There are records of tsunamis reaching heights of more than 100 feet.
Tsunamis may strike in a matter of minutes (following an earthquake) or within hours, depending on how far the epicenter is from Hawaii.
Warnings and notifications will be passed promptly by one or more of the following means:
- The 15th Wing command post
- The15th Wing Web page www.15thwing.af.mil
- The 15th Wing Facebook page: https://www.facebook.com/15thWing
- On base siren system: a long steady tone followed by a warning message.
- Off base siren system: a long steady tone followed by a warning message.
To be safe, throughout the event of a tsunami, listen carefully to TV or radio reports. More current tsunami information can be found at the National Weather Service's Pacific Tsunami Warning Center Web site at www.prh.noaa.gov/ptwc.
Don't go back to low-lying areas until the watch or warning expires or is cancelled!
TSUNAMI SAFETY RULES
1. All earthquakes do not cause tsunamis, but many do. When you hear that an earthquake has occurred, tune into a reputable news source for emergency information.
2. An earthquake in your area is a natural tsunami warning. If you are at the beach and feel violent shaking (enough to knock you off-balance) wait for it to stop, and then move quickly to higher ground. If a tsunami is generated, it will arrive in a few minutes. Do not stay in low-lying coastal areas after a strong earthquake has been felt.
3. A tsunami is not a single wave, but a series of waves. Stay out of danger areas until an "all-clear" is issued by a competent authority.
4. Approaching tsunamis are sometimes preceded by a noticeable rise or fall of coastal water. This is nature's tsunami warning and should be heeded.
5. A small tsunami at one point on the shore can be extremely large a few miles away. Don't let the modest size of one make you lose respect for all.
6. All warning to the public must be taken very seriously, even if some are for non-destructive events. The tsunami of May, 1960 killed 61 people in Hilo, Hawaii, because some thought it was just another false alarm.
7. All tsunamis, like typhoons, are potentially dangerous, though they may not damage every coastline they strike.
8. Never go down to the shore to watch for a tsunami. When you can see the wave, you are too close to escape it. Never try to surf a tsunami; most tsunamis are like a flash flood full of debris and they do not curl or break like surging waves.
9. Sooner or later, tsunamis visit every coastline in the Pacific. Warnings apply to you if you live in any Pacific coastal area.
10. During a tsunami emergency, your local police and on-base officials will try to save your life. Give them your fullest cooperation.