A tsunami is a powerful series of ocean waves typically caused by large-scale disturbances, most commonly significant earthquakes beneath or near the ocean floor. Unlike regular wind-driven waves, tsunamis involve the entire water column from the seafloor to the surface. They can travel across entire ocean basins at speeds comparable to a jet plane, slowing down but increasing in height as they approach shallower coastal areas. Recognizing these signs is important for personal safety in coastal regions.
Official Warning Systems
Official tsunami warning systems detect and forecast these powerful waves. International and national centers, such as the Pacific Tsunami Warning Center (PTWC) in Hawaii and the National Tsunami Warning Center (NTWC) in Alaska, continuously monitor seismic activity and sea levels. These centers utilize seismic sensors to rapidly detect earthquakes and deep-ocean assessment and reporting of tsunamis (DART) buoys and coastal tide gauges to confirm a tsunami’s presence and measure its characteristics.
Upon detection, these warning centers issue various levels of alerts: Tsunami Watches, Advisories, and Warnings. A Tsunami Watch indicates a distant earthquake has occurred and a tsunami is possible, prompting readiness. A Tsunami Advisory signals strong currents or waves are expected, dangerous to those near the water, requiring people to stay out of the water and away from beaches. A Tsunami Warning means a dangerous tsunami is expected or already occurring, necessitating immediate action and evacuation. These alerts are disseminated through multiple channels, including emergency broadcasts, sirens, text messages, weather radios, and social media.
Natural Warning Signs
Observing natural signs can provide the earliest indication of a tsunami, especially for those located close to the source. One of the most significant signs is feeling a strong earthquake, particularly one that makes standing difficult or lasts for an extended period. If such shaking occurs in a coastal area, a tsunami could arrive within minutes, even before any official warning.
Another natural sign is a sudden and unusual recession of ocean water from the shoreline. The ocean may pull back much farther than a typical low tide, exposing the seabed, reefs, or fish. This phenomenon, often called “drawback,” indicates that the trough of the tsunami wave is reaching the coast before the crest, and the subsequent crest could arrive rapidly.
A loud, unusual sound emanating from the ocean can also signal an approaching tsunami. This sound is frequently described as a roar, similar to a freight train or jet aircraft. Additionally, observing a large, unusual wave or an approaching wall of water distinctly different from normal ocean swells indicates immediate danger.
Immediate Actions When a Tsunami is Imminent
When official alerts are issued or natural warning signs are observed, immediate action is required. The most important step is to evacuate coastal areas and move to higher ground as quickly as possible. This means moving inland, away from the water, to an elevation of at least 100 feet (about 30 meters) above sea level.
If natural warning signs are present, such as strong ground shaking or a sudden ocean recession, do not wait for official instructions. A tsunami generated by a nearby earthquake can arrive within minutes, leaving insufficient time for formal alerts. Walk, run, or cycle to higher ground, as roads may become impassable due to damage or congestion.
Stay away from the coast, beaches, and harbors during a tsunami warning, as the danger can persist for hours with multiple waves arriving. If designated tsunami evacuation routes are available, follow them to guide individuals to safer locations efficiently. After evacuating, remain in the safe area until authorities issue an “all clear” message. Returning too soon could expose individuals to subsequent, potentially larger, tsunami waves or hazardous debris.