Tsunami trap: the Ediz Hook dilemma
By Eric Scigliano, Washington Sea Grant
Dwellers on Washington’s seismically active, highly exposed coasts face a daunting range of hazards, including devastating periodic earthquakes and tsunamis. Offshore lies the Cascadia Subduction Zone, where one continental plate slowly pushes under another. Pressure builds along this fault line until it releases via earthquakes that may top 9 on the moment magnitude scale. Geologic evidence suggests the region is due for another.
The tsunami generated by such a quake could reach communities on Washington’s ocean coast within 20 minutes and larger towns on the Strait of Juan de Fuca in less than an hour. Many of them are unprepared for such a catastrophe.
Washington Sea Grant’s coastal specialists, Jamie Mooney and Ian Miller, are doing everything they can to provide the tools these communities need to anticipate and survive the eventual tsunami. They disseminate the latest tsunami science and safety strategies via both formal and informal forums, from a statewide Coastal Hazards Resilience Network coordinating federal, state, and local planning efforts, which Mooney is working to build, to Miller’s popular blog, Coast Nerd Gazette. Mooney works to connect the tsunami modelers at NOAA’s Pacific Marine Environmental Laboratory with the communities and agencies that can benefit most from their findings. Mooney and Miller both conduct tsunami-preparedness trainings wherever coastal residents are willing to listen.
Two such trainings that Miller gave this year on an especially vulnerable site are already bearing fruit. Midway along the Strait of Juan de Fuca lies Ediz Hook, a three-mile sand spit that curves around Port Angeles, the largest city on Washington’s Olympic Peninsula. It is occupied by a salmon farm, boat launch, and two critical operations dedicated to keeping everyone else on these waters safe: the Puget Sound Pilots, who guide every tanker, freighter, and cruise ship that leaves or enters Puget Sound, and the U.S. Coast Guard’s Air Station/Sector Field Office Port Angeles. On weekends, when visitors stroll the Spit, there may be more than 250 people there.
In January and February, Miller conducted training sessions for the pilots and Coast Guard. He explained how a major quake and tsunami would affect the coast now. The Hook would of course be inundated, but the pilots were particularly alarmed to learn what would likely happen if they tried to escape over the narrow land bridge. br>
“We keep training people, ‘Run to higher ground, run to higher ground,’” says Jamye Wisecup, the emergency management coordinator for Clallam County, where Port Angeles lies. “We just always expected to evacuate by land.
That’s where Ian came into the picture. He said, ‘How about using a water route?’—because we won’t be able to get to higher ground.’”
An 80-year-old paper mill straddles the only road to the mainland, with a steel causeway overhead and large oil tanks nearby. Miller, a geologist by training, told the pilots how a quake’s shaking amplification would jar the loose sand and gravel underneath. “The ground shakes more on unconsolidated sediments than it does on bedrock,” he explains. “The additional shaking increases the odds that either the single road off the hook would be buckled, folded or damaged, or that power lines and poles along the road would be toppled, or that the buildings associated with the mill could fall down and block the road.“
“It was compelling,” says Eric vonBrandenfels, vice president of the Puget Sound Pilots, “and it rattled everybody a lot.” Thus spurred, the pilots are trying to devise a waterborne escape plan. On this score, vonBrandenfels says, they’re in a better position than their Coastie neighbors: the pilots’ two 70-foot boats “ are ready 24-7” to ferry them out to passing ships, whereas the Coast Guard’s larger cutters could take longer to launch.
Even so, vonBrandenfels says, when the pilots conducted a trial, “it took us two hours to get loaded and off. At that point we’d be under 30 feet of water.”
But at least they’re alerted to the danger, and to the urgency of finding a solution. “Ian did a great job,” says vonBrandenfels. “I’m just a pilot. When I talk about this stuff, people look at each other and think, ‘Is this guy crazy?’ But when Ian tells them, they listen. He’s got the science, and the science is irrefutable.”