A tsunami can strike a coastline within minutes of an earthquake or arrive hours later from across the ocean. Knowing exactly what to do in each phase, before, during, and after, is the difference between a close call and a catastrophe. Tsunamis travel up to 600 mph in deep water and rush ashore not as a single breaking wave but as a fast-rising flood that can last for hours or even days.
Before: Know the Warning Signs
Official alerts aren’t always the first signal. Nature often gives you a head start if you know what to look for. A strong earthquake that lasts 20 seconds or more, or one violent enough to knock you off your feet, is a natural tsunami warning on its own. A rapid, unusual drop or rise in sea level along the shore is another major red flag. If the ocean suddenly pulls back and exposes the seafloor, do not go look. That receding water is being drawn into the incoming wave. A loud, sustained roar from the ocean is also a sign to move immediately.
If you live in or are visiting a coastal area, learn the evacuation routes before you ever need them. Most tsunami-prone communities post blue-and-white evacuation route signs. Walk or drive the route at least once so it’s familiar under stress. Identify the nearest high ground or a reinforced concrete building of at least four stories. Keep a go-bag with water, medications, a flashlight, a battery-powered radio, copies of important documents, and a whistle for signaling rescuers.
Before: Understand the Alert Levels
The U.S. tsunami alert system uses four levels, and each calls for a different response:
- Warning: Dangerous coastal flooding and powerful currents are imminent or already happening. Move to high ground or inland immediately.
- Advisory: Strong currents and waves dangerous to anyone in or near the water. Stay off beaches and away from harbors and marinas. Significant inland flooding is not expected.
- Watch: A tsunami may impact the area later. The threat level hasn’t been confirmed yet. Stay tuned to emergency broadcasts and be ready to act quickly if the watch is upgraded.
- Information Statement: An earthquake has occurred but no threat has been identified. No action needed.
A warning can be issued with very little lead time, so treat any strong coastal earthquake as your personal warning. Don’t wait for an official alert to start moving.
During: Get to High Ground Fast
If you feel a long or violent earthquake near the coast, or you see the ocean behaving strangely, head inland or uphill right away. Move on foot if traffic is likely to jam. You need to get above the expected inundation zone, and every minute counts. Don’t stop to gather belongings. Don’t return for pets if it means losing critical evacuation time.
If high ground isn’t reachable, vertical evacuation is your backup plan. Look for a reinforced concrete or steel-reinforced concrete building and get to the fourth floor or higher. The structure should be earthquake-resistant, and ideally it won’t face directly toward the ocean. Buildings designated as vertical evacuation sites are engineered for short-term protection of 12 to 24 hours and built to withstand both earthquake shaking and tsunami forces. In places like Honolulu, official policy directs people to the fourth floor or above in steel or reinforced concrete buildings, or to buildings 10 stories or taller.
If you’re on a boat in deep water or very close to it, put on life jackets immediately and head straight out to sea. Washington state guidance recommends reaching at least 100 fathoms (600 feet) of depth or the deepest water you can find directly offshore. Steer into the waves and stay well clear of other vessels. If you’re on a boat near shore, you’ll need to judge quickly whether you have time to reach deep water or whether abandoning the boat and heading to high ground on foot is safer. Factor in the time before waves arrive, current weather, and road or ramp congestion.
During: Stay Put Until the Danger Passes
This is the part that catches people off guard. A tsunami is not one wave. It’s a series of waves called a wave train, and the time between crests ranges from about five minutes to two hours. The first wave is often not the largest. The peak flooding typically arrives a couple of hours after the initial wave, and dangerous currents and flooding can persist for days in some locations.
Do not return to low-lying areas after the first wave recedes. Stay on high ground or in your evacuation shelter until local officials issue an all-clear. Listen to a battery-powered or hand-crank radio for updates. Near the coast, the wave slows from its deep-ocean speed to roughly 20 to 30 mph, but that’s still faster than you can run, and the water carries heavy debris that turns into battering rams.
After: Don’t Rush Back
Even after waves stop arriving, the danger isn’t over. Floodwaters left behind are contaminated. Tsunami water submerges drinking wells and mixes in bacteria, viruses, and parasites that can cause cholera, chronic diarrhea, and serious infections. Chemical contaminants are common too: fuel from overturned tanks, pesticides swept from storage areas, and industrial runoff. Even using this water to clean a small cut can lead to a dangerous infection. Brackish water, the saltwater-freshwater mix that saturates coastal areas after a tsunami, is also unsafe for drinking or cooking because of its high salt content.
Wait for official clearance before returning to any affected area. When you do go back, approach your home carefully. Look for sagging roofs, walls that lean or bow, foundation cracks, doors that won’t open, and missing support beams. Any of these signs mean the structure could collapse. Don’t go inside. Check for downed power lines from a distance and never touch them. Look for gas leaks (smell or hissing sounds) and water line damage. Shut off gas and water valves if you can do so safely, and contact the utility company to report problems.
If your home appears structurally sound, have a licensed contractor or structural engineer confirm it before you move back in. Floodwater inside the home will have left behind the same biological and chemical contamination found outdoors. Anything porous that was submerged, including drywall, insulation, carpet, and upholstered furniture, will likely need to be removed. Do not assume tap water is safe until your local water authority confirms it. Use only bottled or properly treated water for drinking, cooking, brushing teeth, and cleaning wounds.
After: Protect Yourself During Cleanup
Post-tsunami debris fields contain shattered glass, nails, splintered wood, displaced appliances, and potentially hazardous chemicals. Wear thick-soled shoes, heavy gloves, and long sleeves when sorting through wreckage. Avoid wading through standing water whenever possible. If you must, cover any open wounds with waterproof bandages first. Wash your hands thoroughly with clean water and soap after any contact with floodwater or debris.
Photograph damage to your property before moving or discarding anything. This documentation is essential for insurance claims and disaster assistance applications. If you were displaced, register with local emergency services or FEMA to access recovery resources. Emotional recovery takes time too. Communities that have been through a tsunami often experience prolonged stress, sleep disruption, and anxiety about future events, especially among children. Local disaster relief organizations typically offer counseling services in the weeks and months following a major event.