Washington’s coast needs up to 80 tsunami escape towers. It has two now
When a tsunami is headed your way, the only escape might be to go up.
Washington’s coast is woefully unprepared for that option. High ground is scarce and every second counts, according to a new state assessment. What’s more, Washington becomes more due for a major earthquake with every passing year.
“We’re certainly in that window. It can happen at any time,” said Maximilian Dixon, the geologic hazards supervisor for the Washington Emergency Management Division. “And it’s definitely something that keeps you up at night.”
The agency wanted to know how many people who live in tsunami inundation areas in Cascadia Subduction Zone could benefit from an evacuation tower or other form of vertical refuge.
According to the assessment, Pacific County needs between 25 and 40 structures, Grays Harbor could use 30-42 structures and Clallam County needs up to three.
As of now, only two evacuation structures exist in Washington. One is part of an elementary school near Westport, and the other is a tower under construction by the Shoalwater Bay Tribe near Tokeland and should be completed in early 2022.
The structures are needed because people might have only a few minutes to walk to safety to avoid a tsunami caused by an offshore 9.0 magnitude earthquake. In some vulnerable areas, it can take up to an hour to walk to safety.
So, why not drive?
“You’re going to have severe damage to bridges, to roadways, fires, liquefaction, trees and telephone poles falling down,” Dixon said. “You’re going to have folks that are potentially panicking, getting into accidents. So the likelihood of someone being able to find their car keys, get into their car and have a clear path to drive to safety is very, very low.”
The last so-called megathrust earthquake and tsunami happened in 1700. Geologic evidence shows they’ve occurred on the Cascadia fault every 400-600 years going back thousands of years. The fault, between two of Earth’s plates, is just offshore. The shift in the seabed causes the resulting tsunami.
The January 1700 tsunami was recorded by historians in Japan. Oral histories of coastal tribes on the North American coast tell of a great earthquake and tsunami that struck on a winter evening that wiped out low-lying villages.
The 50-foot-high tower that will soon rise near Tokeland will have two refuge platforms above the predicted tsunami height. The useable area of 3,400 square feet will accommodate 386 people.
Waves of 60-feet-high are projected to strike Ocean Shores in a major tsunami. Any structure used as a tsunami refuge has to be the height of the tallest predicted wave plus another 30 percent, Dixon said.
Because many refuge structures will be built on sandy soils, it’s important they sit on below-ground piers, Dixon said. A series of waves could wash away soil around the tower’s legs. Another feature that provides stability, he said, is an open leg design which allows water to pass through the structure without destabilizing it.
Designs vary, but most are a combination of concrete, metal and wood.
Evacuation towers were already in place in March 2011 when coastal Japan, a country that has invested billions in earthquake preparedness, was hit by a major tsunami following a 9.0 earthquake off its coast. The towers saved lives, according to UNESCO.
Towers have also been constructed in New Zealand.
The first waves of a tsunami could arrive in 10 to 15 minutes after the ground stops shaking on the Washington coast, Dixon said.
Puget Sound wasn’t part of the study because the kind of mega quake caused by the offshore Cascadia Subduction Zone would give residents at least an hour or more to get to high ground before the first wave hits.
The towers aren’t cheap, often carrying million dollar-plus price tag. But, governments can apply for grants — something now made easier by the study, Dixon said.
“These structures are absolutely essential for saving lives,” Dixon said. “The buildings out there on the coast are, first of all, not high enough, but also they’re not built to withstand the entire force of the ocean, hitting them over and over with multiple waves.”
The study assessed the best location on the highest ground but still within a walkable distance of vulnerable populations, Dixon said. Areas that were deemed both high risk and highly populated included Long Beach in Pacific County, Aberdeen in Grays Harbor County and Neah Bay in Clallam County.
The study also accounted for rising ocean levels from climate change as well as projected subduction, or lowering of the ground, in a major quake.
The assessment was conducted by the University of Washington’s Institute for Hazards Mitigation Planning and Research. It was funded by a NOAA Tsunami Activities grant.
