08/12/2025
Have you wondered why Crescent City has the worst tsunamis on the east pacific coast? It’s not one thing but a combination of factors.
Not My fault in today's Times - Standard (8/10/25)
When it comes to tsunamis, Crescent City is a special place
Lori Dengler for the Times-Standard
Posted August 9, 2025
https://www.times-standard.com/2025/08/09/lori-dengler-when-it-comes-to-tsunamis-crescent-city-is-a-special-place/
The tsunami generated by the July 29 M 8.8 earthquake near Kamchatka demonstrates why Crescent City California has earned the title “tsunami magnet.” By 7 PM PDT on July 30th, the tsunami warning centers in Hawaii and Alaska had cancelled all alert messages, with one exception. An Advisory for the Del Norte County coastline would remain in place for another 12 hours. When the advisory was finally cancelled at 7:17 AM on July 31st, only one place on the planet outside of the coast of Kamchatka and the northern Kuril Islands near the epicenter, had sustained significant damage – Crescent Harbor.
I’ve had a keen interest in Crescent City since I first began studying tsunamis in the 1990s. As part of a study of the likely impacts of a great earthquake in our area, I dug into the literature about past tsunamis. There were numerous publications from the 1960s and 1970s focused on 1964 and why Crescent City had suffered so much damage. Many of those studies were engineering reports and one name kept popping up – Orville Magoon. It’s an unforgettable name and I found reports he had authored from the 1960 tsunami as well. That tsunami came to us from Chile and the 14 hours it took to travel to the North Coast gave Orville enough time to set up some instruments in the Bay Area and Crescent City to record it.
Orville was a coastal engineer working on jetties and coastal protection structures out of the San Francisco Army Corps of Engineers office. He led the design efforts to rebuild the Humboldt jetties in the 1970s and was the first to use steel-reinforced dolosse (massive wave dissipating concrete tetrapods). Jetties and revetment structures may have been Orville’s day job, but tsunamis were his passion. He grew up in Hawaii and at the age of 16 watched the 1946 tsunami atop a tree overhanging the water near his home. Fortunately, he survived the experience and took the opportunity to study them when he could. In 1964, he convinced his bosses to study the tsunami impacts in Crescent City. His carefully constructed map of the damage showed how buildings had been offset and estimated peak inundation heights. It was one of the first post-tsunami field surveys ever conducted.
I attended a conference on coastal hazards in 2002. After my talk, a man approached me and introduced himself as Orville Magoon. My mouth must have dropped, as I blurted out, “Mr. Magoon, I thought you were dead. I’ve read so many of your papers.” My shock must have amused him as we became colleagues, co-authoring several papers over the next decade, and close friends.
Orville gave me a better understanding of the engineering aspects of tsunamis and how every bay and inlet has its own characteristic period of oscillation. Imagine the sound of a bell – a large one will have a deeper and longer lasting tone than a small one. Water bodies are more complicated because there can be smaller and larger features all producing different periods that interfere with one another. He gave me boxes of unpublished reports about the 1964 tsunami. The unique characteristics of Crescent Harbor were addressed. The harbor tends to oscillate with periods on the order of 20 – 25 minutes. But the offshore environment is also important. The continental shelf along Del Norte County is slightly concave and also traps wave energy but those periods are longer. As a result, the waves interfere with each other, causing distinct packets of wave energy that build and decay and can last a long time.
In 2006, a M8.3 earthquake occurred in the Kuril Islands north of Japan. The initial assessment was no damage likely, and no warnings were issued for the West Coast. But the National Tsunami Warning Center was concerned that there could be strong currents at Crescent City and gave us an informal heads up. Strong currents did materialize, and half of the docks and several boats in Citizens Dock, the small boat basin, were badly damaged.
The 2006 tsunami was a big eye opener for me and many colleagues. Why were the currents so strong in the boat basin? I collaborated with Burak Uslu who was then a graduate student doing tsunami modeling at USC. We suspected that the shape of Citizens Dock may have been partly to blame. It had been built after the 1964 tsunami to provide more sheltered anchorage from winter storms, but little consideration of tsunami impacts had been taken into account in the design.
We were able to get water depths in the harbor from before the basin was built and Burak carefully constructed pre- and post-basin grids. He ran 2006 tsunami models for the two different cases. The result confirmed our suspicions – currents in the basin were more than three times higher than they had been in the old harbor before the basin was built. In some areas of the Citizens Dock, they were even stronger.
There’s not just one reason why Crescent Harbor is so vulnerable to tsunamis. The first is straightforward. Crescent City is the only populated spot in Northern California that sits at low elevation and juts into the ocean. The lowest areas in Eureka are protected by the Samoa Peninsula and the shallow Bay. Exposure is always the first factor to consider in tsunami hazards.
The next three reasons are related to factors outside of the Harbor. In last week’s column, I included a model of the modeled Kamchatka tsunami amplitude across the Pacific. Most of the energy is directed perpendicular to the fault rupture, both back towards Kamchatka and outwards into the southeastern Pacific. The shape of the seafloor, seamounts, and the characteristics of fault slip concentrates the tsunami into higher and lower energy zones. One of those zones points straight towards Northern California. This isn’t just a unique feature of the Kamchatka tsunami. Almost every large tsunami coming from the northern, western, or southern Pacific tends to be amplified here by the Pacific seafloor. That amplification affects Humboldt County as well, but our higher elevation and protective Bay makes tsunamis much less of a threat.
Once the tsunami nears the coast, the waves interact with the continental shelf and the coastline. As Orville’s reports showed, tsunamis set up oscillations on the shelf. They are also focused or dissipated by the shape of the coastline. Along the Del Norte coast, the shape swings waves around Battery Point, accelerating them into the Harbor from the south. I was surprised how this boomerang effect caused even the 1964 Alaska tsunami surges to pack their strongest wallop from the south.
It's a complex stew of wave frequencies and amplitudes that make it into the Harbor. They begin to rattle around in the harbor adding a 20-to-25-minute period to the mix. Now there are at least three sets of periods going – the primary signal from the source, oscillations from the shelf and those in the harbor. I’ve greatly simplified the story as there are complexities in the harbor shape and as the currents interact with breakwaters, islands, and other obstructions, eddies form.
Crescent Harbor was vulnerable to tsunamis before Citizens Dock was built. Unfortunately, the design of the basin has exacerbated the threat, turning even modest tsunamis into multimillion dollar losses. The basin entrance is about 200 feet wide, so incoming tsunami surges must accelerate as they squeeze through the narrow or***ce. Once in the basin they rattle around, bouncing off the hard walls and setting up yet another series of sloshes.
After the 2006 and far more damaging 2011 Japan tsunami, Crescent Harbor was repaired and strengthened. Replacing Citizens Dock with a new structures was not an option, but engineers did what they could to create some dampening in the walls and built far more robust docks and pier supports. H dock closest to the entrance was deliberately designed as a sacrificial lamb, to take the brunt of the impact and in doing so, dissipate energy in the rest of the basin. It appears to have worked. H dock suffered significant damage on July 30th, but the rest of the basin is still functioning.
We don’t know the full extent of damage. The currents at Citizens Dock remained too strong for divers to fully investigate the subsurface structures even after the tsunami advisory was cancelled. The good news is that Crescent City and the people who use and work around Citizens Dock and Crescent Harbor are aware of the hazard, conducted a safe evacuation of boasts before the first surges arrived and no one was injured.
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Lori Dengler is an emeritus professor of geology at Cal Poly Humboldt, and an expert in tsunami and earthquake hazards. The opinions expressed are hers and not the Times-Standard’s. All Not My Fault columns are archived online at https://kamome.humboldt.edu/taxonomy/term/5 and may be reused for educational purposes. Leave a message at (707) 826-6019 or email [email protected] for questions and comments about this column or to request copies of the preparedness magazine “Living on Shaky Ground.”
