New tsunami maps released to the public across the river last month have important messages for the Washington side, too.

    The outer coastlines of Oregon and Washington have grown accustomed in the past decade to the idea of a near-shore subduction-zone quake unleashing a series of giant ripples that will begin washing over the beach and dunes within 15 minutes. As soon as the shaking subsides enough to allow it, people along the shore must run away from the water and seek the nearest high ground. Any delay whatsoever could cost your life.

    The new maps make it clearer that towns within the Columbia estuary and other coastal rivers are also highly vulnerable. The timing and depth of inundation will depend on various factors — including the tidal stage and local terrain — but it has become obvious since the 2011 Japanese tsunami that flooding can be appreciably deeper and encroach farther inland than previously believed. Estuary residents will have a little more time to get away, but will still have to escape 30 feet of onrushing water.

    Geological studies have found evidence of ground subsidence and tsunami flooding far to the east of even Chinook, which faces a threat of substantial inundation after a major nearby earthquake.

    Along the ocean shoreline, Oregon geologists now are urging people to prepare for a flood of 70 or even 80 feet in a worse-case scenario break of our local Cascadia subduction zone. This is highly theoretical, but even so it should help shape land planning decisions and emergency preparations.

    In Long Beach, for example, it calls into question plans to construct a vertical evacuation mound of 34 feet, only about half as high as these new estimates suggest is necessary. An argument can be made that it is better to make a start toward a partial answer than do nothing at all. But Oregon’s numbers urge a dramatic shift toward more aggressive preparations.

    New tsunami maps won’t mean a thing if there’s a giant earthquake in the middle of the night and people don’t know where the nearest safe zone is. Two o’clock in the morning is no time to be figuring out for the first time which street or trail to run along toward high ground.

    All this is manageable. Most coastal residents will survive even the worst of these events that happen every 200 to 500 years. You want to make sure you and your loved ones are among those who get to proudly wear “I survived the great tsunami” T-shirts.

    Anyone living less than 50 to 70 feet above sea level should take time, sooner rather than later, to practice walking to the nearest area that is at least that elevation. It’s also important to pack a small evacuation bag to grab on your way out the door, containing items such as matches, energy bars and essential medications. Coastal evacuees may get little help for several days, particularly if a major quake results in significant damage in major cities along the Interstate 5 corridor.

    Although coastal planning has primarily focused on the series of tsunamis that follow a subduction seismic event, steps should also be considered for preparing for the quake itself. Fairly simple projects like anchoring heavy bookcases and water heaters to walls can alleviate the danger of major injuries. It will be impossible to run from a tsunami with a broken leg.

    All this is manageable. Most coastal residents will survive even the worst of these events that happen every 200 to 500 years. You want to make sure you and your loved ones are among those who get to proudly wear “I survived the great tsunami” T-shirts.

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