Special Report: What we don't know might kill us

December 08, 2006 11:00 pm

By Cornelia de Bruin

Triplicate staff writer

No one knows exactly why Crescent City is a magnet for tsunamis, but one local scientist has a theory.

The ocean floor's topography off the Northern California coast maybe channeling and amplifying tsunami waves so that they hit Crescent City like a brick tossed from a skyscraper – while the rest of the pavement or shoreline isn't struck by another stronger than a feather.

Because Crescent City is the only area suffering major damage on Nov. 15, Humboldt State university Geology Department Chairwoman Lori Dengler's theory may finally be proven. She predicts "a lot of emphasis" from National Oceanic and Atmospheric Administration mappers on getting better data about the ocean floor west of here that curves waves around to point into Crescent City Harbor — a harbor she describes as "excitable."

"The bottom line is that we don't know why, but the big problem is the shape of the shore, the location of Point Saint George Reef and the way waves wrap around," she said. "This is still a research project, but it will probably be tackled this year."

What's needed is better mapping of the ocean floor, called bathymetry, for oceanic administration researchers to use in studies called modeling, Dengler said.

Modeling tries to reproduce what's happened before and use the results as predictors of what will happen — in Crescent City Harbor's case, with tides, called marigrams when they're plotted on graphs.

In determining whether the Nov. 15 Kuril Island quake of magnitude 9.1 warranted a tsunami watch/warning situation, researchers relied on marigram predictions.

"They found incredibly good matches of data everywhere but Crescent City, which was way off," she said.

Once predictions become more accurate, Dengler said efforts to minimize damage can be better thought out.

Although they probably won't result in a solution used by the residents of Okushiri, Japan, they will result in "a better type of warning to residents and visitors here."

Okushiri residents, sick of being hit by tsunamis, built a 30-foot seawall around their harbor. They haven't had tsunami damage since, but the view is boring.

"I expect in two to three years that Allen Winogradov will get a product that shows what the marigram (tide wave graph) will look like," Dengler said. "It will also give us a better way to determine what our Cascadia event hazards are."

Another change coming involves fine-tuning the internal warning system that NOAA's National Weather Service West Coast Alaska Tsunami Warning Center uses.

Part of the reason it did not call a warning here is because it does not have the capability to send a warning to a single area.

"It's a regional system, and this brought up the need to refine the system," Dengler said.

She said the June 14, 2005 evacuation of Crescent City came because of a warning for the entire California coast sent from Alaska.

"There was lots of over-evacuation (in Crescent City)," she said. "You need to know if you're in the evacuation zone or not, if you're not, you don't have to go."

Dengler said that for the most part, downtown Crescent City is not a problem to evacuate. Its one notable exception is the Surf Hotel — home to a large concentration of the medically fragile population: those who need help.

"They will be fine in a 1964-sized distant tsunami, but if it's bigger, they'll have to do a vertical evacuation," Dengler said.

South of town, however, she called "a real problem." The area's evacuation route directs its residents to walk parallel to the beach for one to two miles before it can gain altitude.

"I would like to see wooden walkways across the marshes," Dengler said. Evacuees can't across the marshes, and there's no perpendicular route.

So far, Dengler says we've been lucky.

"We've had two events where no one was hurt, but we can't count on having three," she said Lori Dengler, professor and chair of the Humboldt State University Geology department. "I've never felt more optimistic that something good will come from this, and I've been doing this since about 1980."