Is there such a thing as Tsunami Season? No. A tsunami can strike anywhere along an ocean coast at any time and can be very dangerous to life and property. While it is important if you live, work or play on the coast, to prepare for a tsunami, it is also important to realize that the effects can reach far inland following waterways and low spots causing extensive inland flooding. Meteotsunamis occur inland as well, especially along the Great Lakes.
What is a tsunami?
A tsunami is not a "Tidal Wave" as movies so often dramatically portray Tsunamis are a series of waves (not just one) caused by a large and sudden disturbance of the sea. Most tsunamis are caused by undersea earthquakes, but not all earthquakes cause tsunamis, and smaller earthquakes at or near water may cause tsunami-like results in large bodies of water other than oceans.
Not all tsunamis act the same. And, an individual tsunami may impact coasts differently. A small tsunami in one place may be very large a few miles away.The speed of a tsunami depends on the depth of the ocean. In the deep ocean, tsunami waves are barely noticeable but can move as fast as a jet plane, over 500 mph. As the waves enter shallow water near land, they slow to approximately 20 or 30 mph. That is still faster than a person can run.
As the waves slow down, they can grow in height and currents intensify. Most tsunami waves are less than 10 feet high, but in extreme cases, can exceed 100 feet. When a tsunami comes ashore, it will not look like a normal wind wave. It may look like a fast-rising flood or a wall of water. Sometimes, before the water rushes on land, it will drain away suddenly, showing the ocean floor, reefs and fish like a very low tide. Tsunamis can travel up rivers and streams that lead to the ocean. A large tsunami can flood low-lying coastal areas more than a mile inland.
The series of waves that flood, drain away and then reflood the land may last for hours. The time between waves ranges from five minutes to an hour. The first wave to reach the shore may not be the largest or the most damaging. It is not possible to predict how long a tsunami will last, how many waves there will be, or how much time there will be between waves.
Tsunamis are among the most powerful and destructive natural forces. Tsunami waves radiate outward in all directions from the causal disturbance and can move across entire ocean basins. Most tsunamis are caused by undersea earthquakes, but can also be caused by landslides, volcanic activity, certain types of weather and meteorites. Weather occurrences, too can cause meteotsunamis, especially along the Gulf of Mexico and large water bodies such as the Great Lakes.
What is a Meteotsunami?
Meteotsunamis have characteristics similar to earthquake-generated tsunamis, but are caused by air pressure disturbances often associated with fast moving weather systems, such as squall lines.
These disturbances can generate waves in the ocean that travel at the same speed as the overhead weather system. Development of a meteotsunami depends on several factors such as the intensity, direction, and speed of the disturbance as it travels over a water body with a depth that enhances wave magnification.
Like an earthquake-generated tsunami, a meteotsunami affects the entire water column and can become dangerous when it hits shallow water, which causes it to slow down and increase in height and intensity. Even greater magnification can occur in semi-enclosed water bodies like harbors, inlets, and bays.
Meteotsunamis are regional in nature. In the United States, conditions for destructive meteotsunamis are most favorable along the East Coast, Gulf of Mexico, and in the Great Lakes, where they may pose a greater threat than earthquake-generated tsunamis.
As Weather Ready Nation Ambassadors, we strongly urge you to learn what to do before, during and after a tsunami that could save your life and the lives of your family and friends.
Most of the things you need to do to prepare for a tsunami are basic disaster survival steps you should follow to prepare for the other hazards that may impact your community. Some actions, however, are unique to tsunamis since response time may be limited.
- Find out if your home, school, workplace or other frequently visited places are in tsunami hazard or evacuation zones and if your community has had tsunamis in the past. Your local emergency management office, your state's geologic or tsunami hazard website and your local National Weather Service Weather Forecast Office are good resources for information about your risk.
- Find out if your community is TsunamiReady. Communities recognized by the National Weather Service as TsunamiReady are better prepared for tsunamis.
There are two ways that you may be warned that a tsunami is coming: an official tsunami warning and a natural tsunami warning. Both are equally important. You may not get both. Be prepared to respond immediately to whatever you hear or see first.
- An official tsunami warning will be broadcast through local radio and television, wireless emergency alerts, NOAA Weather Radio and NOAA websites (like Tsunami.gov). It may also come through outdoor sirens, local officials, text message alerts and telephone notifications.
- There may not always be time to wait for an official tsunami warning. A natural tsunami warning may your first, best or only warning that a tsunami is on its way. Natural tsunami warnings include strong or long earthquakes, a loud roar (like a train or an airplane) from the ocean, and unusual ocean behavior. The ocean could look like a fast-rising flood or a wall of water. Or, it could drain away suddenly, showing the ocean floor, reefs and fish like a very low tide. If you experience any of these warnings, even just one, a tsunami could be coming.
- Get a battery-operated NOAA Weather Radio to receive official alerts and other hazard information 24 hours a day, 7 days a week.
- Sign up for email and text message alerts from your local emergency management office and make sure your mobile devices are set to receive wireless emergency alerts.
- Make an emergency plan and a family communication plan and put together a portable disaster supplies kit that is easily accessible and contains basic items you and your family may need in any emergency. Include your pets in all your preparedness efforts. Since you do not know where you will be when disaster strikes, prepare kits for work and your car, too.
- Meet with your family to discuss the plan and why you need to prepare for a disaster.
- Practice your plan and keep it up to date.
- Be a role model. Share your knowledge and plans with friends and neighbors so they can prepare themselves and their loved ones.
If your home, school, workplace or other frequently visited places are in tsunami hazard or evacuation zones, your emergency plan should include evacuation plans.
- Find out from your local emergency management office if there are evacuation routes and assembly areas identified for your community and if a map is available.
- If assembly areas are not identified, plan to evacuate to a safe place that is on high ground or inland (away from the coast) and outside the tsunami hazard or evacuation zone. You may need to identify more than one safe place, depending on where you may be when you get a tsunami warning (e.g., home, work, etc.). You should plan to be able to reach your safe place on foot if you can because of possible road damage, closed roads and traffic jams. If you are concerned that you will not be able to reach a safe place in time, ask your local emergency management office about vertical evacuation. Some strong (e.g., reinforced concrete) and tall buildings may be able to provide protection if no other options are available.
- Map out evacuation routes to your safe place(s) from your home, workplace or any other place you visit often that is in a tsunami hazard or evacuation zone.
- Practice walking your evacuation routes, including at night and in bad weather. Familiarity with the routes will make evacuation quicker and easier if you ever need to evacuate for real.
- If you have children that go to school in a tsunami hazard or evacuation zone, find out about the school's plans for evacuating and keeping the children safe. Find out where the assembly area is and where you should pick up your children after the danger has passed.
- If you are visiting an area at risk for a tsunami, find out about local tsunami safety. Your hotel or campground may be able to provide you with tsunami warning and evacuation information. It is important to know this information before a warning is issued. You may not have a lot of time after a warning. You do not want to waste it figuring out what to do.
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If you are on a boat and you get a tsunami warning, your response will depend on the size of the tsunami, the currents it produces, where you are, how much time you have before the first wave arrives and the weather at sea. If you are a boat owner or captain:
- Make sure you have a way to receive tsunami warnings when you are on the water. The U.S. Coast Guard will issue urgent marine information broadcasts on your marine VHF radio's channel 16. Additional information will be available from NOAA Weather Radio.
- Find out how to respond to a tsunami warning and what to do if you are at sea when a damaging tsunami strikes your coast. Your harbor master, port captain, the U.S. Coast Guard and local and state emergency management offices are the best sources for tsunami safety information and regulations for boaters in your area.
- Make a plan and put together a disaster supplies kit to keep on board your boat. Be sure this includes a proper marine first aid kit. Be aware that shore facilities may be damaged, so if you are at sea during a tsunami, you may not be able to return to the harbor you left. Be prepared to remain at sea for a day or more.
We are located in coastal San Diego, and see how silly and unprepared people can be - during tsunami warnings, we see many rushing to the water to watch, rather than away from the danger. During a tsunami, dangerous coastal flooding and powerful currents are possible and may continue for several hours or days after initial arrival. The first wave may not be the last or the largest. Follow directions and respond to tsunami warnings when given...
How you respond to a tsunami warning depends on where you are and how you receive the warning. There are two types of tsunami warnings, official and natural. Both are equally important and suggest the potential for a tsunami that may cause widespread flooding. You may not get both types of warnings. Be prepared to respond to whatever you hear or see first. For your safety and others, always follow instructions from local officials.
If you are outside of the tsunami hazard or evacuation zone and you receive an official or natural tsunami warning, a tsunami is possible or likely, but you are in a safe place. Stay where you are unless local officials tell you otherwise.
Official Tsunami Warning
If you are anywhere in a tsunami hazard or evacuation zone or a low-lying coastal area and you receive an official tsunami warning, a tsunami is likely. The warning will estimate the tsunami's arrival time, describe potential impacts and recommend actions to take.
- Stay out of the water and away from beaches and waterways.
- Get more information about the threat and what to do from NOAA Weather Radio, local radio or television or your mobile device (text or data). Limit nonemergency phone calls to keep the lines open for emergency communications.
- If local officials ask you to evacuate, implement your emergency plan and move quickly to your safe place outside the hazard or evacuation zone unless officials tell you to go somewhere else. If you do not have a safe place or cannot reach it, follow evacuation signs to safety or go as high or as far inland (away from the water) as possible.
Natural Tsunami Warning
If you are in a tsunami hazard or evacuation zone or a low-lying coastal area and you feel a strong or long earthquake, the ocean acts strange (e.g., it looks like a fast-rising flood or a wall of water or it drains away suddenly, showing the ocean floor like a very low tide) OR there is a loud roar coming from the ocean, a tsunami is possible and could arrive within minutes.
- In case of an earthquake, protect yourself. Drop, cover and hold on. Be prepared for aftershocks, which happen frequently after earthquakes. Each time the earth shakes, drop, cover and hold on.
- Do not wait for an official tsunami warning or for instructions from local officials.
- As soon as you can move safely, implement your emergency plan and move quickly to your safe place outside the hazard or evacuation zone. If you do not have a safe place or cannot reach it, follow evacuation signs to safety or go as high or as far inland (away from the water) as possible.
- When you are in a safe place, get more information about the threat and what to do from NOAA Weather Radio, local radio or television or your mobile device (text or data). Limit nonemergency phone calls to keep the lines open for emergency communications.
- If there is earthquake damage, avoid fallen power lines and stay away from buildings, bridges and piers because heavy objects may fall from them during an aftershock.
- Follow instructions from local officials. It is their job to keep you safe.
- Stay out of the tsunami hazard or evacuation zone until local officials tell you it is safe. The first wave may not be the last or the largest and the danger may last for hours or days.
Note: If you are on the beach or near the water and feel an earthquake—no matter how big or how long it lasts—move quickly off the beach to high ground or inland (away from the water) as soon as you can do so safely.
