Hawaii is vulnerable to tsunamis, which are powerful ocean waves caused by the displacement of a large volume of water. The state’s central position in the vast Pacific Ocean basin exposes it to wave energy originating from almost any direction. These long waves, often incorrectly called tidal waves, travel across the deep ocean at speeds comparable to a jetliner, carrying immense energy toward the islands.
Why Hawaii Is Vulnerable to Tsunamis
Hawaii’s geographical location makes it a frequent recipient of trans-Pacific tsunamis, a risk stemming from the surrounding “Pacific Ring of Fire.” This belt of high seismic and volcanic activity encircles the Pacific Ocean, where tectonic plate boundaries frequently cause large undersea earthquakes. Tsunamis generated along this ring, from locations like Alaska, Chile, or Japan, have a direct path to the Hawaiian Islands. These distant-source tsunamis (teletsunamis) are the most common type to impact Hawaii, offering several hours of warning time before the first wave arrives.
A different, though far rarer, threat comes from local-source tsunamis, generated by earthquakes or large-scale landslides much closer to the islands. The Big Island is particularly susceptible to these, often from seismic activity along the south flank of the Kīlauea volcano. When a local event occurs, the tsunami can reach nearby shores in mere minutes, meaning the ground shaking itself becomes the only natural warning. Areas at the greatest risk are generally those less than 25 feet above sea level and within a mile of the shoreline.
Major Historical Tsunami Events
The destructive potential of distant-source events was demonstrated by the 1946 Aleutian Islands tsunami. An earthquake of magnitude 8.6 near Alaska generated waves that reached Hawaii approximately four and a half hours later, causing surges up to 55 feet high in some areas. This event resulted in 159 fatalities and extensive destruction, particularly in Hilo on the Big Island, and directly led to the establishment of the Pacific Tsunami Warning Center.
Another significant event was the 1960 tsunami, triggered by a magnitude 9.5 earthquake off the coast of Chile, the largest ever recorded. The waves took about 15 hours to travel across the Pacific. Despite warnings, 61 people died in Hilo, where waves reached heights of up to 35 feet. The destruction in Hilo was so extensive that the residential area of Shinmachi was destroyed and not rebuilt. A more recent example is the 2011 tsunami from the magnitude 9.1 Japan earthquake. Effective warnings gave residents over eight hours to evacuate, resulting in no fatalities in Hawaii, though the state sustained about $30 million in damages.
The Hawaii Tsunami Warning System
The state relies on a sophisticated system centered around the Pacific Tsunami Warning Center (PTWC), located on Oʻahu. The PTWC monitors seismic and sea-level data across the Pacific basin using a network of seismic stations and deep-ocean sensors to analyze the potential for a tsunami and calculate its estimated arrival time. This monitoring allows for the issuance of alerts that fall into three main categories: Watch, Advisory, and Warning.
A Tsunami Watch is the lowest alert level, indicating a distant earthquake has occurred that may generate a tsunami, prompting close monitoring. A Tsunami Advisory is issued when a tsunami is expected to cause strong currents or waves dangerous to people near the water, but widespread coastal flooding is not anticipated. The most serious alert is a Tsunami Warning, which signifies that a dangerous, widespread tsunami is imminent or already occurring, requiring immediate evacuation of designated zones. These alerts are relayed to the public through the Emergency Alert System (EAS), wireless emergency alerts, and a network of outdoor warning sirens.
Personal Safety and Evacuation Protocols
Immediate action is necessary when an official Tsunami Warning is issued or when a natural warning sign is observed. The primary goal is to move inland and uphill as quickly as possible, away from designated evacuation zones. When a severe earthquake occurs—one strong enough to make standing difficult—the ground shaking serves as the only warning for a local-source tsunami. This requires immediate self-evacuation without waiting for official alerts.
If moving to high ground is not immediately feasible, “vertical evacuation” may be a life-saving option. This involves moving to the fourth floor or higher in a reinforced concrete or steel structure that has at least four stories. Other natural signs include an unusual and rapid recession of the ocean water, exposing the sea floor, or hearing a loud roar similar to a jet or train. Since a tsunami is a series of waves, the danger can persist for many hours, and individuals must remain outside the evacuation zone until county officials issue an official “all clear” message.