Tsunami

Know Your Tsunami Terms

Familiarize yourself with these terms to help identify a tsunami hazard:

Advisory

An earthquake has occurred in the Pacific basin, which might generate a tsunami.

Warning

A tsunami was, or may have been generated, which could cause damage; therefore, people in the warned area are strongly advised to evacuate.

Watch

A tsunami was or may have been generated, but is at least two hours travel time to the area in Watch status.

What are Tsunami?

A tsunami (pronounced soo-NAH-mee) is actually a series of traveling ocean waves of extremely long length generated primarily by earthquakes that disrupt the ocean floor, or earthquakes that trigger large underwater landslides. Oceanic volcanoes and even meteorite impact can also cause tsunamis, although these are rarer but equally dangerous.

Contrary to common perceptions, tsunamis are not simply large waves of the sort generated by normal oceanographic and weather conditions. Tsunamis are very different from wind-generated waves because of their ability to sweep ashore for great distances. While it is true that tsunamis may be quite large in height, the true danger is related to the mass of energy that propels them through the ocean at great speeds, and what happens when the tsunami waves reach the shore.

Tsunami waves are also distinguished from ordinary ocean waves by their great length between wave crests, often exceeding 60 miles in the deep ocean, and by the time between these crests (ranging from 10 minutes to one hour). As the waves reach the shallow water of the coastline, the waves slow down and the energy causes the water to pile up into walls of water that can tower 30 to 100 feet in height.

The first tsunamis wave is often followed by a series of additional waves, which complicates efforts to locate and rescue people who may not have escaped in time. For the fire department, lifeguards, law enforcement, and others with responsibility to conduct rescue and other emergency operations, the additional waves represent a constant danger to First Responders. Sometimes the secondary tsunami waves are much larger than the first. Responders cannot use the first tsunami “run up” line as the safety boundary because additional waves may run further inland than the first.

Once a tsunami impacts the shoreline, it behaves very much like a flash flood, tearing through large buildings, carrying other buildings away, sweeping automobiles and people away, and battering them with all the debris that the flood has picked up. Being in front of a tsunami is not much different than being in the path of a dam that has broken: You will be struck by a wall of water carrying trees, rocks, automobiles, boats, and construction debris.

Survivability for victims caught in a tsunami is quite low. Many victims of are beaten and battered by the debris, and then drown. The fortunate ones manage to climb high enough to avoid the main thrust of the current, or are deposited on high ground, or manage to grab branches and buildings and pull themselves from the water. Some are rescued by bystanders, but this is a rare instance because of the forces involved and the suddenness of the event.
Tsunamis have caused some of the most devastating catastrophes in history, including the 2004 Sumatra event that killed more than 200,000 people in 13 nations in Asia and Africa; the eruption of Krakatoa, which killed more than 30,000 people in Indonesia; the destruction of the Minoan civilization in what is now Greece; the series of tsunamis that destroyed much of Lisbon (Portugal), a massive earthquake and tsunami that killed untold numbers of coastal Pacific Northwest Indian tribes 300 years ago, the 1964 Good Friday Earthquake that devastated much of Anchorage (Alaska) and sent a tsunami that killed dozens of people in Crescent City, California, and others.

Tele-tsunamis (those originating far away but traveling through the deep ocean at more than 500 miles per hour) may strike in as little as one to three hours, or perhaps up to twelve hours after the triggering event, depending on the distance from the source. Although tele-tsunamis can potentially be very large, their delayed arrival allows more time to evacuation people from threatened areas and move emergency equipment and personnel into strategic positions for rapid response to an actual tsunami impact.

Near-source tsunamis can be more dangerous in some cases, because they can strike within minutes of an earthquake or underwater landslide, and they can potentially be larger when they strike our coast because their energy has not had time to dissipate. Naturally, near-source tsunamis are a great concern because there is less time to evacuate, less time to position emergency units, and may even impact first responders attempting to warn and evacuate people on the coast, or responding to fires, building collapses, and other emergencies caused by the same large quakes that can cause tsunamis to be generated.

There may be no time to issue official warnings for near-source tsunamis, so it’s very important for the public to understand the critical actions to be taken in potential tsunami inundation zones in the event of a major local earthquake. In the most basic terms, if you feel strong, sustained ground shaking that makes things and people fall down, breaks windows, or causes other damage, IMMEDIATELY MOVE INLAND AND/ OR TO HIGHER GROUND, and let others know to do the same.

Remember, THE BEST WAY TO SURVIVE A TUSNAMI IS TO EVACUATE TO A SAFE LOCATION BEFORE IT STRIKES.

What to do Before and During a Tsunami:

The following are guidelines for what you should do if a tsunami is likely in your area:

Turn on your radio to learn if there is a tsunami warning if an earthquake occurs and you are in a coastal area.

Move inland to higher ground immediately and stay there.

Stay away from the beach. Never go down to the beach to watch a tsunami come in. If you can see the wave you are too close to escape it.

CAUTION

– If there is noticeable recession in water away from the shoreline this is nature’s tsunami warning and it should be heeded. You should move away immediately.

What to do Before and During a Tsunami:
The following are guidelines for what you should do if a tsunami is likely in your area:

Turn on your radio to learn if there is a tsunami warning if an earthquake occurs and you are in a coastal area.

Move inland to higher ground immediately and stay there.

Stay away from the beach. Never go down to the beach to watch a tsunami come in. If you can see the wave you are too close to escape it.

CAUTION

– If there is noticeable recession in water away from the shoreline this is nature’s tsunami warning and it should be heeded. You should move away immediately.

What to Do After a Tsunami:
The following are guidelines for the period following a tsunami:

Stay away from flooded and damaged areas until officials say it is safe to return.

Stay away from debris in the water; it may pose a safety hazard to boats and people.

Save yourself – not your possessions

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