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 he ocean rose up over the Papua New Guinea village in a mighty, 40-foot wave. It crashed across the beach where people lived in stilt-perched huts. The water ripped dwellings and trees from the sand, dragged villagers across the beach, pummelled them into the debris, and drowned them in the lagoon beyond. The wave continued to the far shore of the lagoon, smashing more huts, killing more people, even scooping corpses out of graves. The death toll was 3,000, with 2,000 more missing.
When USC tsunami expert Costas Synolakis and graduate student José Borrero interviewed survivors, the islanders said they had been punished for their impiety and that more waves would surely follow.
More tsunamis will be coming, but they are just as likely to strike Santa Monica as Sisson Lagoon, says Synolakis, a USC civil and environmental engineer and a leading authority on tsunamis.
Synolakis (left) and Borrero
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The modern era of tsunami research began in 1946, when a big one killed 100 people in Hilo, Hawaii. For years, tsunamis were viewed as waves that could traverse thousands of miles of ocean and threaten hundreds of miles of coastlines. And they were thought to be rare, triggered by a quake of at least 7.5 magnitude. Most of this is now known to be wrong.
• Contrary to previous assumptions, tsunamis are often very localized. The tsunami that
annihilated Sisson Lagoon went unnoticed 20 miles up the coast.
• Tsunamis aren’t so rare. Many probably have been mistaken for rogue waves from distant storms.
• And they aren’t necessarily caused by earthquakes. “Tsu-namis triggered by landslides are much more common that we thought,” Synolakis says.
In 1994, a landslide in Skagway, Alaska, triggered a tsunami that caused $24 million of damage and one death. The same year, a tsunami hit the remote French Polynesian island of Fatu Hiva. There, too, a landslide was the catalyst. Recognizing the warning signs, a teacher evacuated the village’s beachfront school, and no one was hurt.
On a nearby island, Borrero saw decades-old coastal damage that villagers couldn’t explain. “These people had had a tsunami, and no one knew about it,” Synolakis says. “There have probably been many, many others.”
Perhaps in our own backyard. “We took some core samples from the Ballona wetlands and the preliminary results suggest that there have been two large tsunamis in Playa Del Rey in the last 400 years,” Synolakis says.
He and Borrero believe the tsunami threat to Southern California is very real. The shoreline’s geology, they note, is similar to that of the north coast of New Guinea. In both areas, a relatively shallow shelf leads to a sudden cliff-like drop-off several miles offshore. This steep submarine slope is unstable and prone to underwater landslides.
Synolakis and Borrero are now evaluating the Southern Califor-nia coast for the state and FEMA. They’re meeting with local emergency services agencies and briefing lifeguards.
“There are already tsunami warning signs going up on beaches in Oregon, which is also threatened,” Synolakis says, “and we will be getting them in Southern California this year.”
In the meantime, if the Finger of God should point at a beach near you, Synolakis has these tips for tsunami-readiness:
• The first clue of a tsunami is a sudden withdrawal of water from the shore. It could recede as much as a half mile or as little as 100 feet. If you notice this happening, don’t just stand there gaping. Run away from the water!
• Don’t seek shelter in your car. Water is about 1,000 times denser than air, Synolakis explains, making a 20-mile-per-hour wave equivalent in destructive force to a 20,000-mile-per-hour wind. A big tsunami can tumble cars like bowling pins, making a parking lot extremely harzardous.
• Climb to higher ground. A 40-foot wave will stop when it hits a 45-foot bluff. Many Southland beaches are protected by natural bluffs. If the ground is flat, keep moving inland as far as you can go. “With even a 3-minute warning from a lifeguard, a lot of people would be saved if they moved immediately to higher ground,” Synolakis says.
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