Anyone living near any coast may be subject to tsunami concerns; those people should become familiar with basic tsunami safety tips.
Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel towards land, they build up to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves.
How to Prepare:
- When in coastal areas, stay alert for tsunami warnings.
- Learn details of the local warning systems.
- Plan an evacuation route that leads to higher ground.
- Know the warning signs of a tsunami’s arrival: rapid rising or falling water along the coast could be a sign. Rumblings well-off shore can sometimes be heard, especially if a quake triggering a tsunami is close.
- Know the difference between a Tsunami Warning and a Tsunami Advisory:
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 re-positioning of ships to deep waters when there is time to safely do so. Warnings may be updated, adjusted geographically, downgraded, or canceled. To provide the earliest possible alert, initial warnings are normally based only on seismic information.
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 are normally updated to continue the advisory, expand/contract affected areas, upgrade to a warning, or cancel the advisory.
Once It Hits:
- Never stay near the shore to watch a tsunami come in.
- Don’t return to a Tsunami Warning area until local authorities give the all-clear.
For more information on the U.S. Tsunami Warning system, visit www.tsunami.gov.
For more information on the NTHMP, see nthmp.tsunami.gov.