A tsunami warning sign is prominently placed near the Bremerton ferry dock in Washington State.

By Gordon Williams 

Fortunately, the mid-January tsunami triggered by an undersea volcanic eruption near the Pacific nation of Tonga caused only minor flooding along the Washington seacoast. Ocean waves never topped three feet and never swept inland to threaten coastal communities.  

The Washington Department of Natural Resources (DNR) warns that next time we might not be so lucky. A report just out from the agency thinks about the unthinkable — a magnitude 9.0 earthquake along the Cascadia subduction zone. That is the 600-mile long fault line that stretches along the Pacific Coast from California to British Columbia.   

The DNR warning is based on new computer models from the Washington Geological Survey. The damage projected by these new models is stunning. Think of a wall of water — as tall as a six-story building — racing in from the coast at great speed. Shock waves from the Tonga event crossed the Pacific at an estimated 820 miles per hour. 

The Washington Emergency Management Division (EMD) pulls no punches in warning of what could happen if you are overtaken by a tsunami. ”Persons caught in the path of a tsunami often have little chance to survive,” EMD warns. “Debris may crush them or they may drown.”  

DNR concedes there is no reason to assume such a quake is likely any time soon. It notes that “The last Cascadia rupture was 321 years ago and experts estimate a 10 to 17 percent chance that Washington experiences another in the next 50 years.” 

If the odds against such a catastrophe are that much in our favor, why did DNR publish this new report anyway? The answer comes from Hilary Franz, Washington Commissioner of Public Lands and director of the Department of Natural Resources. 

Speaking after the Tonga event, Franz said, “While we were lucky to avoid catastrophe from this weekend’s minor tsunami on our coast, the danger should be front of mind and this report shows what we have long known. There won’t be time for our coastal communities to react after a major earthquake, so it’s vital we provide these detailed models and keep our communities safe when — not if — the next Cascadia mega-quake hits.” 

The new DNR modeling tracks the potential impact of a tsunami along the Washington coast from Grays Harbor to Port Townsend. ”The first tsunami waves,” says the report, “would reach LaPush within 10 minutes from the start of the earthquake, with the crest reaching many locations along the Pacific Coast within 30 minutes. The first rising waves of the tsunami also travel into the Strait of Juan de Fuca, reaching Port Angeles about one hour after the quake.” 

We aren’t talking about minor wavelets, either. “Flooding depths on land are expected to reach or exceed 60 feet along most Pacific Coast beaches,” says the DNR report. It warns that flooding could reach about 100 feet at Yellow Banks Beach in Olympic National Park. 

You can expect some advance warning of a tsunami. The National Weather Service maintains two Tsunami Warning Centers that would send out alerts. Those alerts will reach the public through radio and TV, email and text messages, tweets, and warnings from local emergency services. Warning sirens that emit a wailing noise will sound up and down the Washington coast, 

Once you are alerted, the key to surviving a tsunami is to get to high ground — fast. Preparedness advice from the American Red Cross is brief and to the point: 

  • To escape a tsunami, go as high and as far as you can — ideally to a spot 100 feet above sea level or two miles away. 
  • Every foot inland or upward may make a difference. 
  • If you can see a wave, you are too close for safety. 

Plan an escape route when skies are blue and there is no danger heading your way. Understand that your escape may have to be entirely by foot. Even if the quake left roads in your locale usable, the rush of people to escape a tsunami could clog the roads and make them impassable. If you can’t escape inland, where might you go to reach safety? What about a hill or a steel-framed building tall enough so it won’t be inundated. Train your family in how to use the escape route and how to reconnect when everyone reaches safety. 

The one place you don’t want to be when a tsunami hits is close to the water, The Pacific County Emergency Management Agency had to post this warning on its Facebook page as the Tonga tsunami approached: “Droves of people are driving out onto the beach. This is not a spectator event. Please stay off the beach.” 

American Red Cross Northwest Region

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