A tsunami is a series of powerful ocean waves caused by a sudden displacement of water, most often resulting from an underwater earthquake, landslides, or volcanic activity. These waves travel across the ocean at high speeds, slowing down and growing dramatically in height as they approach shallow coastal waters. The destructive potential lies not in a single breaking wave, but in a rapidly rising wall of turbulent water that floods the land, carrying massive debris. While the outcome is often devastating, survival is possible and depends on rapid recognition of warning signs and immediate, decisive action.
Recognizing the Warning Signs
The first indication of danger comes from an official alert system, which is the most reliable prompt for immediate action. Warnings are issued by centers like the National Oceanic and Atmospheric Administration (NOAA) through emergency broadcasts, local sirens, and Wireless Emergency Alerts. Official alerts range from a Tsunami Watch (indicating a distant threat) to a Tsunami Warning (meaning widespread flooding is expected or occurring). Following the instructions of local emergency management officials is necessary once an alert is received.
A tsunami generated by a nearby earthquake may strike before any official warning, making the recognition of natural indicators important. The most immediate natural sign is severe ground shaking, particularly if it lasts for 20 seconds or more near the coast. If an earthquake is felt, people should immediately drop, cover, and hold on until the shaking stops, and then move to safety without waiting for an official “all clear.”
Another unmistakable sign is the sudden and dramatic recession of ocean water, often exposing the seabed and reefs. This phenomenon, known as “drawdown,” happens as the ocean pulls back before the wave trough arrives. If the water retreats unusually far, it is a definitive signal that a large wave is approaching and immediate evacuation is necessary.
A third natural warning is a loud, unusual sound approaching from the ocean, often described as resembling a freight train or a jet aircraft. This roaring noise is created by the turbulent motion of the incoming wave as it nears the shore. Any one of these natural signs—a long earthquake, receding water, or a loud roar—should be treated as an urgent warning to evacuate.
Immediate Actions During the Event
Upon receiving a warning or recognizing a natural sign, the goal is to achieve both vertical and horizontal evacuation. Horizontal evacuation involves moving inland and uphill, away from the coastal hazard zone, aiming for an elevation of at least 100 feet (30 meters) above sea level or one mile (1.6 kilometers) inland. Traveling on foot is generally the fastest and safest method, as roads and bridges may be damaged or quickly become congested.
For people in low-lying coastal areas where moving far inland is impossible, the strategy shifts to vertical evacuation. This involves seeking refuge on the upper floors of a structurally sound, reinforced concrete building, ideally above the third story. These Tsunami Vertical Evacuation Structures (TVES) are sometimes engineered to withstand the lateral forces of tsunami waves, providing a short-term refuge.
A tsunami is not a single wave, but a series of waves, sometimes arriving minutes or hours apart. The first wave is often not the largest, and subsequent waves can be equally or more destructive. Evacuees must remain at their safe location until official authorities issue an “all clear” signal, which may take many hours.
If a person is caught in the turbulent water, the best chance of survival is to grab onto something that floats, such as debris, and attempt to protect the head and airway. This should only be considered a last resort, as the water is filled with crushing debris and the chances of being battered or drowned are extremely high. The focus must be on a rapid and complete evacuation from the inundation zone.
Navigating Post-Tsunami Hazards
Once the immediate wave threat has passed, the environment remains dangerous, and new hazards emerge. The landscape is littered with unstable infrastructure, including collapsed buildings, damaged bridges, and fallen power lines that can electrify standing water. People must avoid entering damaged buildings until they are inspected for structural integrity and should assume all downed wires are live and hazardous.
Floodwaters pose a health risk due to contamination from sewage, industrial chemicals, and bacteria. People should avoid wading through the water and must not consume local water sources until health officials confirm they are safe, as tsunami action can compromise water supplies. All food that has come into contact with floodwaters should be discarded immediately to prevent illness.
Communication and rescue efforts require focus in the aftermath. Individuals should monitor reliable sources, such as NOAA Weather Radio or local television, for updates and instructions from emergency responders. Non-emergency phone calls should be limited to keep cellular and landlines open for ongoing rescue and coordination efforts.
The post-disaster environment can be physically taxing, and health concerns must be addressed promptly. Injuries sustained during the event, as well as the risk of hypothermia from prolonged exposure to cold water, require immediate attention. People should wait for official rescue teams and avoid driving, as roads may be unsafe or needed for emergency vehicles.