“At the first warning, you should run inland as fast as you can and get as high as you can,” says Fal Allen, who had no such opportunity as a 14-year-old boy scout on an overnight beach outing in Hawaii in 1975, when an earthquake jolted the campers awake. The boys could hear boulders tumbling down the cliffs behind them, so they crawled toward the ocean to avoid being crushed. “We looked up,” Allen says, “and it was just this wall of water coming at us.”

A tsunami is not a single wave but a series of waves that can be separated by hours. If, like the scouts, you end up in the water, try to grab something that floats. Allen managed to climb atop the sheet-metal roof of a small building as the first wave washed it free. The roof eventually knocked up against a large rock, to which Allen saw a friend clinging. The boy urged Allen to jump over to the rock. He fell short and found himself submerged just as the wave sucked back out. In a tsunami, the water becomes thick, a blended mash of buildings, cars, trees, rocks and whatever else it encounters. For what seemed like a very long time, Allen was dragged along the bottom in that churn. When it finally stopped, he fought his way through the debris to the surface. “Don’t give up, even when you think you’re going to die,” he says. “You’re stronger than you realize.”

If you’re near the Pacific Ocean, you’re probably in a tsunami risk zone. Don’t live in constant fear, but do notice things like evacuation-route signs and listen for sirens. If something strange happens — the sea suddenly recedes, or you experience an earthquake at the beach — run. Go 100 feet or more above sea level; go a mile inland; or, if you must, go to the top floors of a high, multistory, reinforced concrete building.

After Allen surfaced, he swam and clambered over uprooted trees back to shore and then to higher ground. Two people not far from the campers died that night; more than a dozen more were injured. Allen thinks he survived in part because, as a surfer and diver, he was familiar with the forcefulness of the sea. “It helps to be good at holding your breath,” he says.