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Updated 3:10pm - Apr 16, 2014
Updated 3:46pm - Apr 15, 2014

Home arrow News arrow Northcoast Life arrow Why are we tsunami-prone ?

Why are we tsunami-prone ?

'64 just the worst one—so far 

 

The path of the tsunami, below: 1964 devastation (Photo by Maris Ward courtesy of the Maris Ward family.)
It’s well known that Crescent City is tsunami-prone.

Since 1938, 22 tsunamis have been recorded along our shores, and in the past 150 years no other community in the contiguous U.S. has suffered more from them than we have.

This distinction attracts many tsunami experts to our area, in particular Humboldt State University Geology Professor Lori Dengler.

“Crescent City is an exciting place if you’re interested in tsunamis,” Dengler said during a recent visit to town.

 

She is one of the founding members of the Redwood Coast Tsunami Work Group, an interagency association that works to reduce earthquake and tsunami hazards in Northern California. She is considered by her peers to be one of the preeminent authorities on the West Coast when it comes to earthquakes and tsunamis.

Lori Dengler and one of Crescent City’s high-water marks. (The Daily Triplicate/Bryant Anderson)
  Much of Dengler’s research focuses on the North Coast. She has written a number of papers detailing the events of March 27-28, 1964, when an Alaskan earthquake generated a tsunami that raced across the Pacific Ocean and killed 11 people in Del Norte County.

She has studied why Crescent City experienced the impact that it did on that clear, starlit night, and also why we continue to be susceptible.

A lot has been learned about tsunamis over the past 45 years, and increased scrutiny of Crescent City has brought insight into our precarious situation.

For instance, one of the biggest lessons from the Good Friday Tsunami is that the first waves that hit us are not going to be the biggest, and the surges will be spread over a number of hours.

“I can always say it will never be the first, second or third waves in Crescent City,” Dengler said. “It will always be later.”

One of the major reasons for this  is the shape of our coastline and the location of our harbor. Together they trap a tsunami’s energy, creating a perfect environment for waves to build up in height.


MANY PEOPLE THOUGHT THE WORST WAS OVER

Had this been known in 1964, we might not have lost so many lives.

When the first wave hit at 11:52 p.m., the tide gauge at Citizens Dock recorded a height of 14.5 feet above the Mean Lower Low Water (MLLW). This is the average height over a number of years of the lowest of the two low tides that occur each day. It was near the peak of high tide in Crescent City as the tsunami approached, and the ocean was already 6 feet above the MLLW. This means the first surge was 8 feet above high tide.

This wave caused flooding in Crescent City’s low-lying downtown area, essentially depositing enough water to get the floors wet. Many people had already evacuated the waterfront area, leaving behind their homes and businesses.

By the time a second wave arrived about a half-hour later, the water from the first surge had already retreated, completely draining the harbor. The second wave was smaller than the first, only measuring 12 feet above MLLW.

Many people thought the worst was over at this point. Some returned to assess the damage to their property, while others simply wanted to sate their curiosity.

This is the point where Crescent City’s exposure to the tsunami increased. Two more waves, both larger than the first and only about 25 minutes apart, washed through the town, catching those who had returned off-guard. The third wave came around 1:20 a.m. and broke the tide gauge, making its exact height unknown. But based on measurements from high-water marks, the fourth and biggest wave reached a height of 22 feet above MLLW.

“In ’64, you’ve got a community that is far more familiar with tsunamis than the old-timers may let you believe,” Dengler said. “Crescent City was tsunami-savvy in 1964, and that led directly to their downfall.”

Del Norters had a different name for tsunamis back then.

“At our time we called them tidal waves,” longtime Crescent City resident and tsunami survivor Bob Ames said in an interview last year. “The word ‘tsunami’ came as a result of education.”

The distinction can be confusing. Look up “tidal wave in a dictionary  you’ll get nearly the same definition as you get for the word “tsunami.” But according to scientists, there’s a major distinction between the two.

“Technically a tidal wave is not a tsunami, but in the vernacular, ‘tidal wave’ has been the term used in English to describe a tsunami,” Dengler said. “We don’t really like to use that anymore because a tsunami is not caused by the tides.”


WHEN THE LAND SNAPS, HUGE WATER DISPLACEMENT

A tsunami’s cause is geologic, not  lunar. A variety of natural disasters that displace large amounts of water. Culprits include volcanic eruptions, submarine landslides and even asteroids crashing into the earth. But by far the most frequent cause of tsunamis are subduction zone earthquakes that buckle the sea floor and send out massive waves.

According to Dr. Walter Mooney, a research seismologist with the United States Geological Survey, a subduction zone is a place where the earth’s crust, which is made up of numerous moving tectonic plates, is being pulled by gravity back into the planet’s mantle. This process is essentially recycling the Earth’s outer shell.

“It doesn’t do so in a continuous manner,” Mooney said of this conveyor belt-like action. “It undergoes this episodic behavior, which we call earthquakes.”

Subduction zone events are different from the more common “strike-slip” temblors, in which tectonic plates rub back and forth on a fault line, causing the ground to shake.

Instead, as the heavier oceanic plate tries to slide under the other, it sticks. The pressure from the force starts to build up and it slowly bends the top, continental plate upward.

Eventually, this compression becomes too great, Mooney said, and the crust snaps back, rebounding like a spring.

“It can’t take it anymore and it goes, ‘Bang!’” Mooney said. “The result is the sea floor is suddenly uplifted.”

This jolt pushes the water up in a burst of energy. The ocean lifts, and a tsunami is born.

This sequence occurred in 1964 when Alaska’s Prince William Sound  snapped. The 9.2 magnitude earthquake’s rupture zone was 500 miles long and about 150 miles wide. Parts of the ground rose more than 30 feet, while others sank by as much as 7 feet.

The resulting tsunami rippled outward at speeds of up to 500 mph from the epicenter.

Unlike ordinary wind waves, a tsunami’s energy stretches from the sea floor to the surface.

While its breadth reaches to the greatest depths of the ocean, in deep water its appearance on the surface is subtle.

“You wouldn’t notice it at all,” Dengler said. “It’s a very, very gentle bulge.”

Though wave lengths can span hundreds of miles in the open ocean, the height of the waves might only be a couple feet. This has left many fishermen oblivious to the devastation of their homeland, even though a large tsunami has passed under the hull of their boat.

The momentum of a tsunami can carry for thousands of miles, from one end of the ocean to the other. But some places tend to be more susceptible than others, especially Northern California.

‘FICKLE FINGER OF FATE’ MAKES US A MAGNET

There’s what Dengler calls a “Fickle Finger of Fate” that points at the North Coast. This is the Mendocino Fracture Zone, and underwater ridge that extends thousands of miles due west from Cape Mendocino.

This scar is visible in satellite images, and Dengler said the sea floor directly north of the fracture zone is more shallow than it is to the south.

“Fishermen say going south across that boundary is like going into the deep end because the water drops so abruptly,” she said. “We actually get a slightly larger tsunami just north of Cape Mendocino rather then just south of it.”

A tsunami’s speed is a direct function of how deep the ocean is. The greater the depth, the faster the wave. As the tsunami hits shallow water approaching a coastline, friction causes the the wave to slow down. And it doesn’t just tap on the brakes, both feet are down.

“You still can’t outrun it,” Dengler said, “but it’s going a lot slower.”

A tsunami that had been traveling almost as fast as a commercial jetliner in the deep ocean slows 25-30 mph when it reaches shore. This change in speed “causes the water to bunch up because that fast-moving water behind it catches up to it,” Dengler said.

The shallower ocean depth north of the Mendocino Fracture Zone means a tsunami’s amplitude will be larger than in other parts of California.

“That actually acts as a wave guide, it concentrates the wave energy,” Dengler said. “We just basically have a bigger incoming wave from almost any other place in the Pacific along the Northern California Coast.”

Further funneling the impact of a tsunami toward Crescent City, is the shape of our portion of the continental shelf.

California’s northern coastline resembles a backward C-shape from Crescent City down to Cape Mendocino. Inside of this is another curve between Point St. George in Del Norte County and Patrick’s Point in Humboldt County.

“Our shelf seems to be kind of bowl-shaped,” Dengler said. “Energy sort of gets trapped and that’s why the tsunami tends to last a long time.”

Another multiplying factor locally is the position of our harbor the natural bend of our beach that gives Crescent City its name.

“It’s this crescent-shaped bay that again tends to amplify the tsunami energy,” Dengler said. “The natural geometry of the harbor seems to welcome tsunamis from all directions.”


A DEADLY VISITOR ROUNDS THE BEND

In 1964, even though the Good Friday Tsunami came from the north, the waves never broke over the jetty, and instead came into the harbor from the opposite direction.

“The tsunami attack sort of came from the southwest,” Dengler said. “It funnels from the south.”

Deeper water offshore allows a tsunami to travel faster farther away from the coastline. As the tsunami approached Crescent City and its harbor the water started to slow down, but  fast waves farther out at sea actually bent the tsunami inland.

“That causes it to literally swing around into the harbor,” Dengler said.

Once there, the energy from the tsunami got trapped inside and started to bounce around. This rebounding, which also occurred on a larger scale outside the harbor from Point St. George down to Patrick’s Point and even further to Cape Mendocino further increased the size of the tsunami’s waves.

“It actually excites oscillations,” Dengler said. “Crescent City rings like a bell.”

Like dropping a rock into a pond, you get more than just one wave in a tsunami. These waves slosh back and forth along the North Coast and within Crescent City’s harbor. This energy can stick around for hours and even days, building upon itself and increasing the size of waves.

Troy Nicolini of the National Weather Service in Eureka describes this motion as the “bathtub affect,” and he said it’s particularly pronounced inside Crescent City’s harbor.

“You can imagine that when a wave comes in there it bounces off the concrete walls. It just bounces and keeps most of its energy,” Nicolini said. “It stays in there long enough for the next wave to come in and now they’re both bouncing around.”

He said this is like putting two kids in a bathtub together. When they both start splashing around, the water resonate off the sides of the tub becoming more turbulent and eventually winding up on the floor.

This doesn’t happen in Humboldt Bay because it “shallows out” and the wave doesn’t have anything to reflect off of, Nicolini said.

“It’s the verticalness of the walls inside the Crescent City Harbor,” he said. “When those waves come in they bounce around in there before they die.”


THESE DAYS, WE’RE MORE VULNERABLE THAN EVER

The harbor is even more vulnerable to tsunamis today than it was in 1964. Recent research by Dengler has found that the inner small boat basin actually focuses a tsunami’s energy once it’s in the harbor.

“It’s not going to make the tsunami any higher, all it does is funnel it,” Dengler said. “You’re forcing all that water into a narrow opening.”

This makes even small tsunamis potentially devastating. In 2006, an earthquake near Russia’s Kuril Islands sent waves across the Pacific and into Crescent City. Though the surge was small and never breached land, it pushed into the inner boat basin and caused an estimated $22.5 million in damage to the docks.

“It was a real eye-opener,” Dengler said. “I was as surprised as anybody that there was that much damage.”

But perhaps the No. 1 reason Crescent City has the unfortunate stigma of being a tsunami poster-child is its relation to the ocean.

“It’s low,” Dengler said. “It’s really close to the water and it sticks out. It’s what we call exposure.”

Driving along Pebble Beach Drive and it’s easy to notice the dip in elevation as you head downtown. Nearly 30 city blocks were inundated in the 1964 tsunami, and it destroyed almost 300 homes and businesses.

Dengler said what happened that night is almost the worst-case scenario for a far-field tsunami caused by an earthquake that we don’t feel in a place that we can’t see.

“This is the subduction zone story,” she said. It’s one we must remember, not only because there will one day be a similar earthquake in a faraway land that will send a tsunami our way, but because we also sit on our own fault line in the the Cascadia Subduction Zone.

“What happened in Alaska is what we will expect in the future in our own homegrown event,” Dengler said. “Someday we will have a similar earthquake here.”



Debris near Elk Creek. (Courtesy Del Norte Historical Society)
The human cost

Eleven people died in Del Norte County in the tsunami. They include:

• Agatha Winifred Clawson, 52, a native of Daleyville, Ind., and co-operator of the Long Branch Tavern on U.S. Highway 101 near Elk Creek. She died after leaving the tavern in a boat with several other people.

• William Clawson, 54, a native of  Oregon and co-operator of the Long Branch. He was also in the boat and died after it overturned.

• Juanita Pearl Edwards, 42, a native of Crescent City and a Long Branch employee. She was also in the boat and died after it overturned.

• Earl Floyd Edwards, 56, a native of Missouri who was employed by Timber Transport. He was also in the boat and died after it overturned.

• Joan Fields, 25, a native of La Grande, Ore. She was also in the boat and died after it overturned.

• Adolph Arrigoni, 65, a native of Italy, drowned in his home on B Street.

• James Parks, 63, a Crescent City native and shoe repairman. He died when his trailer on Front Street overturned.

• Lavelle Hillsbury, 36, a native of Blackfoot, Idaho. She was found amidst the debris in Elk Creek.

• William Wright, 10 months, a native of Crescent City. He was torn from the arms of his mother as they attempted to flee from their home near South Beach.

• Bonita Wright, 3, a native of Crescent City. She drowned while fleeing with her mother and younger brother from their home near South Beach.

• Oran Gilbert Magruder, 73, a native of Crescent City and former stage coach operator. He died at home of a heart attack.

• Donald McClure, He drowned at the mouth of the Klamath River after being swept off a log that he was clinging to.

 

More stories from the six part series on the '64 Tsunami:

The waves of destruction 

 Part 1 #2   Tsunami: Not fit for surfing   

Part 2  A night of close calls    
 
Part 3  Riding out the wave   

Part 4  Tsunami at the stairs   

Part 5  In their own words  


To learn more about the '64 Tsunami   

 


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