A tsunami is a series of powerful ocean waves caused by the sudden, large-scale displacement of a body of water, most commonly triggered by underwater earthquakes, specifically those involving vertical movement of the seafloor. Tsunamis can travel across entire ocean basins at speeds comparable to a jet airliner, only slowing down and growing in height as they approach the coast. Because a locally generated tsunami can strike a coastline within minutes, preparedness is the most important factor in survival. Understanding the required actions before, during, and after a tsunami event can provide the necessary margin of safety.
Preparing Your Family and Home
Proactive planning is the foundation of tsunami safety, ensuring your family knows how to respond when a warning is issued. Begin by determining if your home, workplace, or school is in a designated tsunami hazard zone, which is typically a low-lying coastal area. If you live near the coast, identify the fastest evacuation route to a safe zone, which should be at least 100 feet (30 meters) above sea level or one mile (1.6 km) inland.
Practicing your evacuation route is important because roads may become impassable due to traffic or damage, meaning you may need to evacuate on foot. Every household should prepare a portable emergency supply kit for several days. The kit should contain:
- Non-perishable food and bottled water.
- A first-aid kit and essential medications.
- A battery-powered or hand-crank radio to receive official updates.
- Flashlights and extra batteries.
Develop a family communication plan that outlines how you will contact one another if separated, including designating an out-of-state contact person who can relay messages. Securing or moving heavy furniture and appliances is also a practical step, as these items can become dangerous projectiles during a severe earthquake that may precede a tsunami.
Recognizing Natural and Official Warnings
The immediate, life-saving action required during a tsunami threat depends on quickly recognizing both official alerts and natural signs of danger. Official warnings are broadcast through a variety of systems, including sirens, Wireless Emergency Alerts (WEA) on mobile devices, NOAA Weather Radio, and local television and radio stations. These alerts—categorized as a Watch, Advisory, or Warning—provide time-sensitive information about the threat level and necessary actions, with a Tsunami Warning indicating the greatest danger and the need for immediate evacuation.
However, a locally generated tsunami can reach the coast in minutes, leaving insufficient time for an official warning to be issued. In these cases, recognizing natural warning signs becomes a personal first line of defense. A strong earthquake that makes it difficult to stand, or prolonged shaking that lasts for a minute or more, is a primary natural signal that a tsunami may be imminent.
Another significant natural sign is a sudden and unusual receding of ocean water, exposing the seafloor, rocks, and fish. You may also hear a loud, unusual roar from the ocean, sometimes described as sounding like an approaching train or jet aircraft. If you observe any of these natural signs, you must immediately move inland and toward higher ground without waiting for official confirmation, as the wave could arrive within minutes.
Evacuation should be done by foot if possible, as roads may be damaged or congested. Avoid river valleys and low-lying areas, which can funnel the water inland. If you are unable to reach high ground, a vertical evacuation to the third floor or higher of a sturdy, reinforced concrete building is a last-resort option.
Staying Safe After the Tsunami
Remaining safe after the initial event involves understanding that a tsunami is not a single wave but a series of waves that can impact the coast for hours. The first wave to reach the shore is often not the largest or most destructive, and subsequent waves may be even more powerful. Therefore, you must remain in a safe, high-ground location until officials announce that the threat has completely passed and it is safe to return.
Upon returning, exercise extreme caution, as the environment will be filled with hidden hazards. Floodwaters may contain sewage, chemicals, and bacteria, and the water level can be deeper than it appears. Avoid wading through floodwaters and assume that all downed power lines are live, as electrocution is a serious risk when electrical equipment or wiring is wet.
Inspect your home for structural damage before entering, especially checking for foundation cracks or shifted walls. Stay away from any damaged buildings, roads, or bridges. Continue to rely on a battery-powered radio for official updates, as emergency communication systems may be compromised. Do not use tap water until local health authorities confirm it is safe to drink, as tsunami events can contaminate public water supplies.