Data Shows Coastline at Risk of Tsunamis

California’s coastline may be at a higher risk of danger to flooding from a major tsunami, according to data published by the California Geological Survey (CGS).

According to the CGS’s most recent risk assessment, which illustrates the devastation that could result from scenarios considered to be extreme but realistic, a large tsunami could flood large parts of Long Beach, along with Marina del Rey and the nearby dual port complex to an elevation of up to 15 feet above sea level.

In the event of a tsunami, areas of notable concern in Los Angeles County include Marina del Rey, the ports of Long Beach and Los Angeles and around Alamitos Bay due to there being only a few roads for evacuation. According to scenarios used by CGS back in 2021, the first surges of a worst-case tsunami would reportedly reach Los Angeles’ coastline in about six hours.

“That may seem like a lot of time, but it will take an hour or so for the National Tsunami Warning Center to issue a warning to California and then additional time for local authorities to determine whether an evacuation is necessary,” Rick Wilson, then a senior engineering geologist with the California Geological Survey tsunami unit, in a 2021 statement. “The bottom line is, if you’re near the coast and feel strong shaking from a local earthquake or get an official notification to evacuate, move inland as soon as possible.”

Outside of Southern California, areas of the state’s northern coastline are also at risk of danger should a tsunami occur. According to official city documents, a worst-case scenario for the northern coastline would be for a magnitude 9 earthquake to occur on the Cascadia subduction zone, a 600-mile undersea boundary of two colliding tectonic plates.

Should a massive earthquake occur in this area, it would likely bring a tsunami to San Francisco within an hour, as well as send surges of water up to 50 feet high toward Crescent City and 30 feet high along the outer coast of Humboldt Bay and the Eureka area. In this event, some people on the northern coastline might have only 10 minutes to get to an evacuation area after a huge earthquake just offshore.

However, for the residents of California, especially those living alone its coastline, the CGS states that the risk of a tsunami happening in a hazard zone is exceeded by the dangers of knowing the hazard zones exist at all.

“While damaging tsunamis are infrequent in California, they have and do happen. If you live on or visit the coast, you need to be aware of this potential hazard,” said Steve Bohlen, the former head of the CGS, when the last updated tsunami hazard area maps were officially released.

More than 150 tsunamis have hit California’s shore since 1800. Most were barely noticeable, but a few have caused fatalities or significant damage. The most destructive tsunami to hit California was on March 28, 1964, which saw waves 21-feet above sea level sweep into Crescent City, hours after a magnitude 9.2 earthquake occurred in Alaska.

California’s large active offshore faults and unstable submarine slopes can cause tsunami activity along the coast, according to the CGS’s official website, with strong ground shaking from an earthquake being the natural warning that a tsunami might be coming.

The CGS states that if you are on the beach or in a harbor and feel an earthquake, immediately move inland or go to high ground. If strong shaking lasts for 20 seconds or more, everyone within the tsunami evacuation area should evacuate as soon as it is safe to do so.

It is also important to know whether you are in a potential tsunami zone by observing street signs in your area or looking online to see if you are in a tsunami hazard zone, as well as knowing the evacuation routes for your area.

The CGS last updated their tsunami hazard zone maps from 2020-2022. For more information about California’s Tsunami Hazard Zones, you can visit conservation.ca.gov/cgs/tsunami/maps.