Tsunamis: What You Need to Know
Huge earthquakes in Japan recently have shown us the power and devastation of tsunamis.
But what is a tsunami? What do you need to know about it? Triggering Events Tsunamis, also known as seismic waves, start when a large disturbance occurs in or near a body of water.
A trigger can be an earthquake, landslide, volcanic eruption, or even a meteorite.
Waves of water radiate away from the disturbance in all directions.
Depending on the power of the triggering event, these waves can travel at hundreds of miles per hour.
Wall of Water When tsunamis hit land, they can form huge walls of water as much as 100 feet high.
Their height of the walls comes from the power of the original wave combined with the land formation it encounters.
A wave that hits a long, low beach will be much lower in height, although it may travel far inland, leaving destruction in its path.
The same wave, hitting a harbor surrounded by hills, can tower to frightening heights, completely filling the harbor and leaving devastation in its wake.
Risks and Dangers Land within a mile of a shoreline and 25 or fewer feet above sea level is most at risk during a tsunami.
Drowning is the biggest cause of death.
There are two danger points for this.
The first is when water first hits land.
The second is when the water recedes, often quickly and unexpectedly, pulling people out to sea.
Destruction to property can also be devastating.
A powerful tsunami can destroy buildings, carry boats, cars, and other vehicles along as if they were small toys, and disrupt gas lines and other utilities.
Flooding, fires, and contaminated drinking water are some of the hazards often left in the wake of a tsunami.
If a tsunami is coming If you experience a triggering event, such as an earthquake, and are in a coastal area:
Drop everything and get to high ground, away from the coast, immediately.
You won't have time to do anything else.
For those further away, the National Oceanic and Atmospheric Administration (NOAA), a federal agency, issues warning that will help you assess the threat of a tsunami.
Alerts are made available via radio broadcast, cell phone messages, and the internet.
You may also hear them via TV broadcasts.
The NOAA has four classifications for alerts: Advisory Conditions that may lead to a tsunami currently exist and could affect your area.
There is not a significant threat as this time, but local officials may elect to close beaches, evacuate harbors or marinas, and reposition ships to deeper water.
Advisories can persist for several hours, even after an initial wave has hit.
Information Statement This lets you know that an earthquake has occurred or a tsunami alert has been issued for another part of the ocean.
No specific threat to your area is anticipated.
Warning A potentially significant tsunami is imminent or expected.
Local officials may evacuate coastal areas and, time-permitting, reposition ships to deeper water.
Listen to local officials.
Get someplace safe.
Watch Seismic information shows that a tsunami may have been generated.
It is at least two hours away.
Get ready to evacuate if needed.
Keep a watch on the situation to see if the status changes or further information is made available.
But what is a tsunami? What do you need to know about it? Triggering Events Tsunamis, also known as seismic waves, start when a large disturbance occurs in or near a body of water.
A trigger can be an earthquake, landslide, volcanic eruption, or even a meteorite.
Waves of water radiate away from the disturbance in all directions.
Depending on the power of the triggering event, these waves can travel at hundreds of miles per hour.
Wall of Water When tsunamis hit land, they can form huge walls of water as much as 100 feet high.
Their height of the walls comes from the power of the original wave combined with the land formation it encounters.
A wave that hits a long, low beach will be much lower in height, although it may travel far inland, leaving destruction in its path.
The same wave, hitting a harbor surrounded by hills, can tower to frightening heights, completely filling the harbor and leaving devastation in its wake.
Risks and Dangers Land within a mile of a shoreline and 25 or fewer feet above sea level is most at risk during a tsunami.
Drowning is the biggest cause of death.
There are two danger points for this.
The first is when water first hits land.
The second is when the water recedes, often quickly and unexpectedly, pulling people out to sea.
Destruction to property can also be devastating.
A powerful tsunami can destroy buildings, carry boats, cars, and other vehicles along as if they were small toys, and disrupt gas lines and other utilities.
Flooding, fires, and contaminated drinking water are some of the hazards often left in the wake of a tsunami.
If a tsunami is coming If you experience a triggering event, such as an earthquake, and are in a coastal area:
- Turn on your radio to see if there are any tsunami warnings.
- Move inland to higher ground.
Do this right away.
Don't risk your life trying to save possessions if a tsunami may be imminent.
Get to a safe place and stay there. - Stay away from the beach.
Never think you are safe watching a tsunami approach.
If you can see the wave, you are too close to escape it. - If you see water moving noticeably away from the shoreline, get someplace safe immediately.
Water is often sucked away from shore moments before a huge wave hits.
This is nature's warning.
Heed it.
- Stay away from flooded areas until officials say it is safe to return.
What looks safe to you could contain live wires that can cause electrocution, gas leaks, or underwater hazards. - Stay away from debris in the water.
This can pose a danger to boats or pedestrians. - Assume water from faucets is contaminated until officials tell you it is safe to drink.
Along with other problems, severe flooding can make sewage systems overflow.
Drinking water canbe polluted. - Use your radio to get information about where to find aid and shelter.
Local announcements will generally let you know when it is safe to return to home or workplace, and where you should gather for temporary aid.
Drop everything and get to high ground, away from the coast, immediately.
You won't have time to do anything else.
For those further away, the National Oceanic and Atmospheric Administration (NOAA), a federal agency, issues warning that will help you assess the threat of a tsunami.
Alerts are made available via radio broadcast, cell phone messages, and the internet.
You may also hear them via TV broadcasts.
The NOAA has four classifications for alerts: Advisory Conditions that may lead to a tsunami currently exist and could affect your area.
There is not a significant threat as this time, but local officials may elect to close beaches, evacuate harbors or marinas, and reposition ships to deeper water.
Advisories can persist for several hours, even after an initial wave has hit.
Information Statement This lets you know that an earthquake has occurred or a tsunami alert has been issued for another part of the ocean.
No specific threat to your area is anticipated.
Warning A potentially significant tsunami is imminent or expected.
Local officials may evacuate coastal areas and, time-permitting, reposition ships to deeper water.
Listen to local officials.
Get someplace safe.
Watch Seismic information shows that a tsunami may have been generated.
It is at least two hours away.
Get ready to evacuate if needed.
Keep a watch on the situation to see if the status changes or further information is made available.
