Tsunami warnings are not an unfamiliar sight along the West coast. In many areas, warning sirens and signs serve as a terrifying alert for coastal residents, indicating that a wall of water might be approaching. However, it's important to note that tsunamis can strike anywhere along the U.S. coastline, whether it be in the West or the East.

Thursdays Tsunami Alerts in California

On Thursday, people in the northern part of California received tsunami alerts shortly after a 7.0 earthquake hit just off the coast of Humboldt county at 10:44 a.m. The notices advised residents that a tsunami could arrive along the coast starting near Fort Bragg at 11:10 a.m. local time and move along the northern California and southern Oregon coasts, reaching San Francisco at 12:10. Residents within the affected zone were urged to move off the water and beach and evacuate inland beyond tsunami hazard zones. Roadways closest to the epicenter were filled with people driving away from the coast.Tsunamis occur when an underwater earthquake rapidly displaces a large amount of water, creating a large, long wave that gains intensity as it crosses the ocean. When it reaches land, it can cause extremely high waves that can travel far inland and cause significant damage.The word "tsunami" comes from the Japanese for "harbor wave." They are particularly dangerous in harbors where the water can become trapped and compressed, resulting in higher waves. In 1964, a massive 9.2 magnitude earthquake in Alaska led to a tsunami in Crescent City, California five hours later. The quake's epicenter was 1,600 miles from the town, and the resulting wave reached nearly 21 feet, killing 11 people and destroying 29 city blocks.

Previous Tsunami Warnings in the San Francisco Bay Area

The last tsunami warning in the San Francisco Bay Area followed a 9.1 earthquake in Tohoku, Japan in March 2011, which sparked a major nuclear accident at the Fukushima-Daiichi nuclear power plant. In January 2022, a tsunami advisory occurred in the Bay Area region after the Hunga Tonga volcano erupted, causing a tsunami and deadly waves that killed four people and injured others on the island of Tonga.Prior to Thursday's quake in Northern California, the last comparable 7.0 magnitude quake occurred in June 2005 just off the coast northwest of Eureka, prompting a tsunami warning. Researcher Amy Williamson from the University of California, Berkeley's Seismology Lab said that such events can happen. She added that those who experienced Thursday's earthquake were "very fortunate" as it occurred so far offshore.Between 1850 and 2004, 51 credible tsunamis were recorded in San Francisco Bay. Only two of these generated damage - the 1960 Chile earthquake and the 1964 Alaska earthquake, which generated waves of almost 4 feet at the San Francisco Presidio.

The Entire West Coast is at Risk

California is not the only part of the United States at risk for tsunamis. The entire West coast, from California to Oregon, Washington state, and Alaska, faces significant hazards from dangerous waves. All four West coastal states are located on significant offshore or nearshore earthquake fault lines, any of which could trigger an underwater earthquake and tsunami.

Small Tsunami Risk on the East Coast

The East and Gulf coasts generally are not at risk for earthquake-caused tsunamis as they do not have major fault lines running under their coastal areas. However, if there is a huge earthquake across the Atlantic, tsunamis can occur. In 1755, a tsunamis recorded along the eastern coast of North America may have been linked to a massive earthquake that struck the Portuguese capital city. The quake likely registered between a magnitude 8.5 and 9.0 and leveled Lisbon. The wave it generated might have reached the Newfoundland town of Bonavista, with a wave height of up to six feet. The same earthquake must have caused at least some waves in Colonial America, although none were recorded. A model shows the wave reaching the East coast about eight hours after the earthquake.Small tsunamis can also be caused by intense coastal storms, known as meteotsunami. These are not caused by underwater earthquakes or landslides but by metrological conditions. In 2018, a large-scale squall line of severe thunderstorms from Western Pennsylvania to southern New England to Maryland created weather-induced wave activity that generated a small meteotsunami along the coastline. However, the danger was minimal as the wave heights were only between 4.3 and 2.3 inches.