During heavy surf, the ocean pounds up sea foam. “Sea foam, ocean foam, beach foam, or spume is a type of foam created by the agitation of seawater, particularly when it contains higher concentrations of dissolved organic matter derived from sources such as the offshore breakdown of algal blooms.”

During our walk yesterday, a wave swept up a hundred yards over the sand and another ten yards into the rocks. This was nothing unusual. We pay attention, so we knew to move higher onshore and are rarely caught. We are particularly careful where there is no place to escape should a wave sweep all the way up to the green line. We work our way along searching for trash and treasures, but always with one eye on the surf line.

Sneakers are completely unpredictable and quiet. The huge crashing sounds come from a retreated wave meeting an incoming wave. Sneakers result from multiple incoming waves coinciding, a wave picking up energy from the one or ones below—all the water moving the same direction.

The tide was going out when we walked yesterday. There is always the sound of the ocean, but walking the beach we both know enough to look up at the peculiar silence of sneakers.

“You never want to turn your back to the ocean because you don’t know when the next wave is going to come in,” Rankin said.

My mother always said it. Never turn your back on the ocean. Yesterday a teenager was rescued from the surf by a local firefighter in Seaside, just fifteen miles north of us. A sneaker wave had got him. Fortunately, the boy was stuck 500 feet offshore, perhaps on a sandbar. But the water is cold. The surf was heavy. And so very cold. The firefighter got the call and in a wet suit was able to get to the boy, put him on a floatation device and then get the two of them back to shore.

There is a faint line of sea foam halfway up the basalt rocks rimming the shore, far right, from the sneaker we avoided.

Over the past month, two groups of visitors staying in the house next door have taken their children out on the shore, dabbing in the water in outgoing tides. I watched with the emergency number at hand. They didn’t go far into the water, but it was December and the water is cold and sneakers . . . Few drown in the winter because the cold keeps most visitors far from the water.

A few years ago, two adolescent boys played knee-deep in the waves during an outgoing tide in November. A father stood on the sand looking worried. I went out and told him it really was not safe for the boys to be in the surf. He thanked me, looked relieved, and called them back on shore. I think I only confirmed what he knew.

People have drowned. Even people who were strong swimmers. Even people who know these waters.

Never turn your back on the ocean. As a child I was knocked flat onto my stomach in the summer by a sneaker. I swallowed and choked and coughed up seawater. I was fortunate to survive the lesson early.