Earthquake-generated tsunamis not uncommon in US. How bad can they get and where do they hit?

Tsunami warnings are not uncommon along the West coast, where warning sirens and signs in many areas provide a terrifying warning for coastal residents: A wall of water could potentially be coming towards them.

But the reality is that tsunamis could hit anywhere on the U.S. coastline - whether it be in the West or the East.

The warnings were put to use on Thursday when people in the northern portion of California were sent tsunami alerts moments after a 7.0 earthquake struck just off the coast of Humboldt county at 10:44 a.m.

The notices advised residents a tsunami could arrive along the coast starting near Fort Bragg at 11:10 a.m. local time and move along the coast in northern California and southern Oregon, arriving in San Francisco at 12:10. Residents within the zone – stretching from Davenport, California, northwest of Santa Cruz, to the Douglas Lane county line in Oregon – were urged to move off the water and beach and evacuate inland beyond tsunami hazard zones.

Roadways closest to the epicenter were full of people driving away from the coast.

Tsunamis can occur when an underwater earthquake rapidly displaces massive amounts of water, leading to a large, long wave that builds in intensity as it crosses the ocean. When it reaches land it can result in extremely high waves that can move far inland and cause significant damage.

The word tsunami comes from the Japanese for "harbor wave." They are especially dangerous in harbors where the water can become trapped and compressed, causing higher waves.

In 1964, a massive 9.2 magnitude earthquake in Alaska resulted in a tsunami in Crescent City, California five hours later. The quake's epicenter was 1,600 miles from the town. The resulting wave crested at nearly 21 feet, killed 11 people and destroyed 29 city blocks, according to the city.

The last tsunami warning in the San Francisco Bay Area followed a 9.1 earthquake in Tohoku, Japan that sparked a major nuclear accident at the Fukushima-Daiichi nuclear power plant in March 2011, said Amy Williamson, a research scientist at the University of California, Berkeley’s Seismology Lab.

A tsunami advisory in the Bay Area region occurred after the Hunga Tonga volcano erupted causing a tsunami and deadly waves that killed four people and injured others on the island of Tonga in January 2022, Williamson said.

Williamson said 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. “They can happen,” Williamson said.

She added that those who experienced Thursday’s earthquake were “very fortunate” it happened so far offshore.

Between 1850 and 2004, 51 credible tsunamis were recorded in San Francisco Bay, according to 2004 research led by Lori Dengler, a professor emeritus at Cal Poly Humboldt. Only two of those generated damage, the 1960 Chile earthquake and the 1964 Alaska earthquake, which generated waves of almost 4 feet at the San Francisco Presidio, the authors reported.

The entire West coast is at risk for tsunamis

California is by no means 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 the dangerous waves.

All four West coastal states sit on significant offshore or nearshore earthquake fault lines, each of which could trigger an underwater earthquake and tsunami.

Small tsunami risk on the East coast

The East and Gulf coasts aren’t generally at risk for earthquake-caused tsunamis because they do not have major fault lines that run under their coastal areas, according to the United States Geological Service.

That doesn't mean they can't happen if there is a huge earthquake across the Atlantic.

A tsunamis recorded along the eastern coast of North America in 1755 may have been linked to the massive earthquake struck the Portuguese capital city. That 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 in Canada, according to research conducted by the Geological Survey of Canada and others. The resulting wave may have been as high as six feet.

That same earthquake must have caused at least some waves in Colonial America, according to the Pacific Tsunami Warning Center, though none were recorded. A model of the quake and subsequent tsunami shows the wave reaching the East coast about eight hours after the earthquake.

Small tsunamis can also be caused by intense coastal storms, according to the U.S. Tsunami Warning System. These are known as meteotsunami because they are caused not by underwater earthquakes or landslides but by metrological conditions.

On May 15, 2018, a large-scale squall line of severe thunderstorms that stretched from Western Pennsylvania to southern New England to Maryland. This in turn created weather-induced wave activity that generated a small meteotsunami along the coastline.

The danger was minimal, however, because the wave heights were only between 4.3 and 2.3 inches.

Contributing: Terry Collins

This article originally appeared on USA TODAY: tsunamis-earthquakes-destruction-coasts