While the term “tsunami” often evokes images of massive towering waves, experts remind us that many of these disasters can manifest as much smaller swells. On Tuesday night, the National Weather Service forecasted that the waves reaching San Francisco early Wednesday morning would be less than a foot high. Subsequent measurements confirmed this prediction, with recorded waves at 1.2 feet, but fortunately, no damage has been reported in the Bay Area thus far.
Given this context, how safe would a kayaking trip truly have been during such conditions? Experts emphasize that even modest wave heights can conceal considerable dangers. Lori Dengler, a tsunami expert from Cal Poly Humboldt, asserts that the true risk lies not in the height of the water but in the strength of the currents moving in and out. “It’s not how high the water is, it’s how strong that water is flowing in and out,” she explained.
The National Weather Service echoed this sentiment, with meteorologist Dalton Behringer pointing out that while a 1-foot swell might seem insignificant, adding that height to the natural tide cycle can amplify the risk significantly. He explained that this phenomenon results in rapid fluctuations in water levels, akin to going from a low tide to a high tide within a matter of minutes instead of hours. For instance, following Japan’s devastating 2011 earthquake, even a 1-foot tsunami caused notable damage to boats in Santa Cruz.
Jim Pruett, the general manager of Pillar Point Harbor in Half Moon Bay, cautioned that the first, second, or even third waves from a tsunami should not be underestimated. Unlike typical waves that crash, tsunami waves are more like powerful swells, which means they retain significant force. Pruett elaborated, “It may be only a 12-inch wave, but there is a lot of water behind that wave. It has traveled across the Pacific Ocean, and when the swell hits, it doesn’t stop. All that water continues to come in, so it surprises people.”
While Pillar Point is a relatively secure natural harbor, Pruett advised to heed local authorities’ warnings if they advise staying out of the water, away from beaches, or evacuating the area. He noted that often the later tsunami waves can be even more dangerous than the initial ones, stating, “The highest [swell] that we’ve seen so far has come a few hours after the initial wave. With tsunami waves, we can see the wave energy actually build for several hours after the initial waves and then dissipate.”
In light of the tsunami advisory, Pamalah MacNeily, the owner of Blue Waters Kayaking in Tomales Bay, made the decision to cancel a kayak tour. She acknowledged that this was not the first instance where she chose to cancel after a tsunami warning, even when conditions appeared calm. MacNeily reiterated the importance of safety: “We have to be cautious with people’s lives, and we also obey the advisories.”
What actions should individuals take when confronted with smaller tsunami waves? Dengler strongly advises against trying to observe these waves up close. Instead, she recommends monitoring the situation via the National Oceanic and Atmospheric Administration’s website. “This type of tsunami is actually arriving relatively slowly,” she said. “There is really nothing dramatic to see.”
While a 1-foot swell may not appear threatening from a distance, the current and the presence of potentially hazardous objects, such as boats, can present serious risk. Once a swell reaches the shoreline, all the water must flow back into the ocean, resulting in extremely strong currents that can pull people or structures out to sea. Pruett advises swimmers and individuals in smaller crafts to exit the water, while suggesting that larger vessels are safer when out at sea, where they can better navigate swells without being pushed towards the shore.
Pruett highlighted an incident during a tsunami triggered by a volcano in 2022, where even less than a foot of swell raised the harbor levels by 3 to 5 feet, due to the impact at high tide when water levels were already elevated. This demonstrates that even minor wave heights can lead to substantial risks, particularly in vulnerable environments.
Looking forward, how can individuals prepare for future tsunami threats? Pruett reassured that the San Francisco Bay is notably capable of withstanding tsunami-like waves. However, he emphasized that large amounts of water can still be expected to enter the Bay during a tsunami event. The importance of being prepared cannot be overstated, especially considering the findings from a recent simulation demonstrating the potential impact of a tsunami on the bay.
Residents are urged to sign up for alerts and remain informed about the nuances between tsunami warnings, watches, and advisories. Additionally, having a clear evacuation plan is critical in enhancing safety during such emergencies.
Crescent City in Del Norte County was among the areas that experienced the most significant effects from Wednesday’s tsunami, with observed waves of up to 4 feet. Many residents took precautions in advance, retrieving their boats from the water in anticipation of larger swells. Historically, Crescent City endured one of the deadliest tsunamis in the United States in 1964, resulting in 11 fatalities and extensive destruction.
Cal Poly’s Dengler reported seeing wave heights of up to five feet in Hilo, Hawaii, and 15 feet on the coast of Russia, underscoring that tsunami impacts are not confined to one region. She pointed out the complexity of how a tsunami interacts with the coastal landscape: “A tsunami always generates a long train of waves, but then when it hits the coast, it reacts to the shape of the shoreline, the shape of the continental shelf, and the shape of bays.”
All of these factors contribute to oscillations and vibrations, which can lead to wave amplification, particularly in areas like Crescent City. It is crucial for coastal communities to remain vigilant and informed, ensuring that residents understand the risks and are prepared for future tsunami warnings.
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